Paramagnetism

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Paramagnetism

Liquid oxygen (blue) can be suspended between the poles of a strong magnet as a result of its paramagnetism.

Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field. Paramagnetic materials include most chemical elements and some compounds; they have a relative magnetic permeability slightly greater than 1 (i.e., a small positive magnetic susceptibility) and hence are attracted to magnetic fields. The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect and modern measurements on paramagnetic materials are often conducted with a SQUID magnetometer.

Paramagnetism is due to the presence of unpaired electrons in the material, so most atoms with incompletely filled atomic orbitals are paramagnetic, although exceptions such as copper exist. Due to their spin, unpaired electrons have a magnetic dipole moment and act like tiny magnets. An external magnetic field causes the electrons' spins to align parallel to the field, causing a net attraction. Paramagnetic materials include aluminium, oxygen, titanium, and iron oxide (FeO). Therefore, a simple rule of thumb is used in chemistry to determine whether a particle (atom, ion, or molecule) is paramagnetic or diamagnetic: if all electrons in the particle are paired, then the substance made of this particle is diamagnetic; if it has unpaired electrons, then the substance is paramagnetic.

Unlike ferromagnets, paramagnets do not retain any magnetization in the absence of an externally applied magnetic field because thermal motion randomizes the spin orientations. (Some paramagnetic materials retain spin disorder even at absolute zero, meaning they are paramagnetic in the ground state, i.e. in the absence of thermal motion.) Thus the total magnetization drops to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency. The attraction experienced by ferromagnetic materials is non-linear and much stronger, so that it is easily observed, for instance, in the attraction between a refrigerator magnet and the iron of the refrigerator itself.

Relation to electron spins

Constituent atoms or molecules of paramagnetic materials have permanent magnetic moments (dipoles), even in the absence of an applied field. The permanent moment generally is due to the spin of unpaired electrons in atomic or molecular electron orbitals (see Magnetic moment). In pure paramagnetism, the dipoles do not interact with one another and are randomly oriented in the absence of an external field due to thermal agitation, resulting in zero net magnetic moment. When a magnetic field is applied, the dipoles will tend to align with the applied field, resulting in a net magnetic moment in the direction of the applied field. In the classical description, this alignment can be understood to occur due to a torque being provided on the magnetic moments by an applied field, which tries to align the dipoles parallel to the applied field. However, the true origins of the alignment can only be understood via the quantum-mechanical properties of spin and angular momentum.

If there is sufficient energy exchange between neighbouring dipoles, they will interact, and may spontaneously align or anti-align and form magnetic domains, resulting in ferromagnetism (permanent magnets) or antiferromagnetism, respectively. Paramagnetic behavior can also be observed in ferromagnetic materials that are above their Curie temperature, and in antiferromagnets above their Néel temperature. At these temperatures, the available thermal energy simply overcomes the interaction energy between the spins.

In general, paramagnetic effects are quite small: the magnetic susceptibility is of the order of 10⁻³ to 10⁻⁵ for most paramagnets, but may be as high as 10⁻¹ for synthetic paramagnets such as ferrofluids.

Delocalization

Selected Pauli-paramagnetic metals

Material	Magnetic susceptibility, ${\displaystyle {\chi }_v}$ [10−5] (SI units)
Tungsten	6.8
Caesium	5.1
Aluminium	2.2
Lithium	1.4
Magnesium	1.2
Sodium	0.72

In conductive materials, the electrons are delocalized, that is, they travel through the solid more or less as free electrons. Conductivity can be understood in a band structure picture as arising from the incomplete filling of energy bands. In an ordinary nonmagnetic conductor the conduction band is identical for both spin-up and spin-down electrons. When a magnetic field is applied, the conduction band splits apart into a spin-up and a spin-down band due to the difference in magnetic potential energy for spin-up and spin-down electrons. Since the Fermi level must be identical for both bands, this means that there will be a small surplus of the type of spin in the band that moved downwards. This effect is a weak form of paramagnetism known as Pauli paramagnetism.

The effect always competes with a diamagnetic response of opposite sign due to all the core electrons of the atoms. Stronger forms of magnetism usually require localized rather than itinerant electrons. However, in some cases a band structure can result in which there are two delocalized sub-bands with states of opposite spins that have different energies. If one subband is preferentially filled over the other, one can have itinerant ferromagnetic order. This situation usually only occurs in relatively narrow (d-)bands, which are poorly delocalized.

s and p electrons

Generally, strong delocalization in a solid due to large overlap with neighboring wave functions means that there will be a large Fermi velocity; this means that the number of electrons in a band is less sensitive to shifts in that band's energy, implying a weak magnetism. This is why s- and p-type metals are typically either Pauli-paramagnetic or as in the case of gold even diamagnetic. In the latter case the diamagnetic contribution from the closed shell inner electrons simply wins over the weak paramagnetic term of the almost free electrons.

d and f electrons

Stronger magnetic effects are typically only observed when d or f electrons are involved. Particularly the latter are usually strongly localized. Moreover, the size of the magnetic moment on a lanthanide atom can be quite large as it can carry up to 7 unpaired electrons in the case of gadolinium(III) (hence its use in MRI). The high magnetic moments associated with lanthanides is one reason why superstrong magnets are typically based on elements like neodymium or samarium.

Molecular localization

The above picture is a generalization as it pertains to materials with an extended lattice rather than a molecular structure. Molecular structure can also lead to localization of electrons. Although there are usually energetic reasons why a molecular structure results such that it does not exhibit partly filled orbitals (i.e. unpaired spins), some non-closed shell moieties do occur in nature. Molecular oxygen is a good example. Even in the frozen solid it contains di-radical molecules resulting in paramagnetic behavior. The unpaired spins reside in orbitals derived from oxygen p wave functions, but the overlap is limited to the one neighbor in the O₂ molecules. The distances to other oxygen atoms in the lattice remain too large to lead to delocalization and the magnetic moments remain unpaired.

Theory

The Bohr–Van Leeuwen theorem proves that there cannot be any diamagnetism or paramagnetism in a purely classical system. The paramagnetic response has then two possible quantum origins, either coming from permanent magnetic moments of the ions or from the spatial motion of the conduction electrons inside the material. Both descriptions are given below.

Curie's law

Main article: Curie's law

For low levels of magnetization, the magnetization of paramagnets follows what is known as Curie's law, at least approximately. This law indicates that the susceptibility, ${\displaystyle \chi }$, of paramagnetic materials is inversely proportional to their temperature, i.e. that materials become more magnetic at lower temperatures. The mathematical expression is: $${\displaystyle \mathbf{M}=\chi \mathbf{H}=\frac{C}{T}\mathbf{H}}$$ where:

• ${\displaystyle \mathbf{M}}$ is the resulting magnetization, measured in amperes/meter (A/m),
• ${\displaystyle \chi }$ is the volume magnetic susceptibility (dimensionless),
• ${\displaystyle H}$ is the auxiliary magnetic field (A/m),
• ${\displaystyle T}$ is absolute temperature, measured in kelvins (K),
• ${\displaystyle C}$ is a material-specific Curie constant (K).

Curie's law is valid under the commonly encountered conditions of low magnetization (μ_BH ≲ k_BT), but does not apply in the high-field/low-temperature regime where saturation of magnetization occurs (μ_BH ≳ k_BT) and magnetic dipoles are all aligned with the applied field. When the dipoles are aligned, increasing the external field will not increase the total magnetization since there can be no further alignment.

For a paramagnetic ion with noninteracting magnetic moments with angular momentum J, the Curie constant is related to the individual ions' magnetic moments, $${\displaystyle C=\frac{n}{3k_{\mathrm{B}}}{\mu }_{\mathrm{e}\mathrm{f}\mathrm{f}}^2\text{ where }{\mu }_{\mathrm{e}\mathrm{f}\mathrm{f}}=g_J{\mu }_{\mathrm{B}}\sqrt{J(J+1)}.}$$

where n is the number of atoms per unit volume. The parameter μ_eff is interpreted as the effective magnetic moment per paramagnetic ion. If one uses a classical treatment with molecular magnetic moments represented as discrete magnetic dipoles, μ, a Curie Law expression of the same form will emerge with μ appearing in place of μ_eff.

Derivation

Curie's Law can be derived by considering a substance with noninteracting magnetic moments with angular momentum J. If orbital contributions to the magnetic moment are negligible (a common case), then in what follows J = S. If we apply a magnetic field along what we choose to call the z-axis, the energy levels of each paramagnetic center will experience Zeeman splitting of its energy levels, each with a z-component labeled by M_J (or just M_S for the spin-only magnetic case). Applying semiclassical Boltzmann statistics, the magnetization of such a substance is $${\displaystyle n\overline{m}=\frac{n\sum _{M_J=-J}^J{\mu }_{M_J}{e}^{-E_{M_J}/k_{\mathrm{B}}T}}{\sum _{M_J=-J}^J{e}^{-E_{M_J}/k_{\mathrm{B}}T}}=\frac{n\sum _{M_J=-J}^J{M}_J{g}_J{\mu }_{\mathrm{B}}{e}^{M_J{g}_J{\mu }_{\mathrm{B}}H/k_{\mathrm{B}}T}}{\sum _{M_J=-J}^J{e}^{M_J{g}_J{\mu }_{\mathrm{B}}H/k_{\mathrm{B}}T}}.}$$

Where ${\displaystyle {\mu }_{M_J}}$ is the z-component of the magnetic moment for each Zeeman level, so ${\displaystyle {\mu }_{M_J}=M_J{g}_J{\mu }_{\mathrm{B}}-{\mu }_{\mathrm{B}}}$ is called the Bohr magneton and g_J is the Landé g-factor, which reduces to the free-electron g-factor, g_S when J = S. (in this treatment, we assume that the x- and y-components of the magnetization, averaged over all molecules, cancel out because the field applied along the z-axis leave them randomly oriented.) The energy of each Zeeman level is ${\displaystyle E_{M_J}=-M_J{g}_J{\mu }_{\mathrm{B}}H}$. For temperatures over a few K, ${\displaystyle M_J{g}_J{\mu }_{\mathrm{B}}H/k_{\mathrm{B}}T\ll 1}$, and we can apply the approximation ${\displaystyle e^{M_J{g}_J{\mu }_{\mathrm{B}}H/k_{\mathrm{B}}T}\simeq 1+M_J{g}_J{\mu }_{\mathrm{B}}H/k_{\mathrm{B}}T}$: $${\displaystyle \overline{m}=\frac{\sum _{M_J=-J}^J{M}_J{g}_J{\mu }_{\mathrm{B}}{e}^{M_J{g}_J{\mu }_{\mathrm{B}}H/k_{\mathrm{B}}T}}{\sum _{M_J=-J}^J{e}^{M_J{g}_J{\mu }_{\mathrm{B}}H/k_{\mathrm{B}}T}}\simeq g_J{\mu }_{\mathrm{B}}\frac{\sum _{M_J=-J}^J{M}_J\left(1+M_J{g}_J{\mu }_{\mathrm{B}}H/k_{\mathrm{B}}T\right)}{\sum _{M_J=-J}^J\left(1+M_J{g}_J{\mu }_{\mathrm{B}}H/k_{\mathrm{B}}T\right)}=\frac{g_J^2{\mu }_{\mathrm{B}}^{2}H}{k_{\mathrm{B}}T}\frac{\sum _{-J}^J{M}_J^2}{\sum _{M_J=-J}^J(1)},}$$ which yields: $${\displaystyle \overline{m}=\frac{g_J^2{\mu }_{\mathrm{B}}^{2}H}{3k_{\mathrm{B}}T}J(J+1).}$$ The bulk magnetization is then ${\displaystyle M=n\overline{m}=\frac{n}{3k_{\mathrm{B}}T}\left[g_J^{2}J(J+1){\mu }_{\mathrm{B}}^2\right]H,}$ and the susceptibility is given by $${\displaystyle \chi =\frac{\mathrm{\partial }{M}_{\mathrm{m}}}{\mathrm{\partial }H}=\frac{n}{3k_{\mathrm{B}}T}{\mu }_{\mathrm{e}\mathrm{f}\mathrm{f}}^2\text{ ; and }{\mu }_{\mathrm{e}\mathrm{f}\mathrm{f}}=g_J\sqrt{J(J+1)}{\mu }_{\mathrm{B}}.}$$

When orbital angular momentum contributions to the magnetic moment are small, as occurs for most organic radicals or for octahedral transition metal complexes with d³ or high-spin d⁵ configurations, the effective magnetic moment takes the form ( with g-factor g_e = 2.0023... ≈ 2), $${\displaystyle {\mu }_{\mathrm{e}\mathrm{f}\mathrm{f}}\simeq 2\sqrt{S(S+1)}{\mu }_{\mathrm{B}}=\sqrt{N_{\mathrm{u}}(N_{\mathrm{u}}+2)}{\mu }_{\mathrm{B}},}$$ where N_u is the number of unpaired electrons. In other transition metal complexes this yields a useful, if somewhat cruder, estimate.

When Curie constant is null, second order effects that couple the ground state with the excited states can also lead to a paramagnetic susceptibility independent of the temperature, known as Van Vleck susceptibility.

Pauli paramagnetism

For some alkali metals and noble metals, conduction electrons are weakly interacting and delocalized in space forming a Fermi gas. For these materials one contribution to the magnetic response comes from the interaction between the electron spins and the magnetic field known as Pauli paramagnetism. For a small magnetic field ${\displaystyle \mathbf{H}}$, the additional energy per electron from the interaction between an electron spin and the magnetic field is given by:

${\displaystyle \mathrm{\Delta }E=-{\mu }_0\mathbf{H}\cdot {\mathit{\mu }}_e=-{\mu }_0\mathbf{H}\cdot \left(-g_e\frac{{\mu }_{\mathrm{B}}}{\hslash }\mathbf{S}\right)=\pm {\mu }_0{\mu }_{\mathrm{B}}H,}$

where ${\displaystyle {\mu }_0}$ is the vacuum permeability, ${\displaystyle {\mathit{\mu }}_e}$ is the electron magnetic moment, ${\displaystyle {\mu }_{\mathrm{B}}}$ is the Bohr magneton, ${\displaystyle \hslash }$ is the reduced Planck constant, and the g-factor cancels with the spin ${\displaystyle \mathbf{S}=\pm \hslash /2}$. The ${\displaystyle \pm }$ indicates that the sign is positive (negative) when the electron spin component in the direction of ${\displaystyle \mathbf{H}}$ is parallel (antiparallel) to the magnetic field.

In a metal, the application of an external magnetic field increases the density of electrons with spins antiparallel with the field and lowers the density of the electrons with opposite spin. Note: The arrows in this picture indicate spin direction, not magnetic moment.

For low temperatures with respect to the Fermi temperature ${\displaystyle T_{\mathrm{F}}}$ (around 10⁴ kelvins for metals), the number density of electrons ${\displaystyle n_{\uparrow }}$ (${\displaystyle n_{\downarrow }}$) pointing parallel (antiparallel) to the magnetic field can be written as:

${\displaystyle n_{\uparrow }\approx \frac{n_e}{2}-\frac{{\mu }_0{\mu }_{\mathrm{B}}}{2}g(E_{\mathrm{F}})H;\left(n_{\downarrow }\approx \frac{n_e}{2}+\frac{{\mu }_0{\mu }_{\mathrm{B}}}{2}g(E_{\mathrm{F}})H\right),}$

with ${\displaystyle n_e}$ the total free-electrons density and ${\displaystyle g(E_{\mathrm{F}})}$ the electronic density of states (number of states per energy per volume) at the Fermi energy ${\displaystyle E_{\mathrm{F}}}$.

In this approximation the magnetization is given as the magnetic moment of one electron times the difference in densities:

${\displaystyle M={\mu }_{\mathrm{B}}(n_{\downarrow }-n_{\uparrow })={\mu }_0{\mu }_{\mathrm{B}}^{2}g(E_{\mathrm{F}})H,}$

which yields a positive paramagnetic susceptibility independent of temperature:

${\displaystyle {\chi }_{\mathrm{P}}={\mu }_0{\mu }_{\mathrm{B}}^{2}g(E_{\mathrm{F}}).}$

The Pauli paramagnetic susceptibility is a macroscopic effect and has to be contrasted with Landau diamagnetic susceptibility which is equal to minus one third of Pauli's and also comes from delocalized electrons. The Pauli susceptibility comes from the spin interaction with the magnetic field while the Landau susceptibility comes from the spatial motion of the electrons and it is independent of the spin. In doped semiconductors the ratio between Landau's and Pauli's susceptibilities changes as the effective mass of the charge carriers ${\displaystyle m^{\ast }}$ can differ from the electron mass ${\displaystyle m_e}$.

The magnetic response calculated for a gas of electrons is not the full picture as the magnetic susceptibility coming from the ions has to be included. Additionally, these formulas may break down for confined systems that differ from the bulk, like quantum dots, or for high fields, as demonstrated in the De Haas-Van Alphen effect.

Pauli paramagnetism is named after the physicist Wolfgang Pauli. Before Pauli's theory, the lack of a strong Curie paramagnetism in metals was an open problem as the leading Drude model could not account for this contribution without the use of quantum statistics. Pauli paramagnetism and Landau diamagnetism are essentially applications of the spin and the free electron model, the first is due to intrinsic spin of electrons; the second is due to their orbital motion.

Examples of paramagnets

Materials that are called "paramagnets" are most often those that exhibit, at least over an appreciable temperature range, magnetic susceptibilities that adhere to the Curie or Curie–Weiss laws. In principle any system that contains atoms, ions, or molecules with unpaired spins can be called a paramagnet, but the interactions between them need to be carefully considered.

Systems with minimal interactions

The narrowest definition would be: a system with unpaired spins that do not interact with each other. In this narrowest sense, the only pure paramagnet is a dilute gas of monatomic hydrogen atoms. Each atom has one non-interacting unpaired electron.

A gas of lithium atoms already possess two paired core electrons that produce a diamagnetic response of opposite sign. Strictly speaking Li is a mixed system therefore, although admittedly the diamagnetic component is weak and often neglected. In the case of heavier elements the diamagnetic contribution becomes more important and in the case of metallic gold it dominates the properties. The element hydrogen is virtually never called 'paramagnetic' because the monatomic gas is stable only at extremely high temperature; H atoms combine to form molecular H₂ and in so doing, the magnetic moments are lost (quenched), because of the spins pair. Hydrogen is therefore diamagnetic and the same holds true for many other elements. Although the electronic configuration of the individual atoms (and ions) of most elements contain unpaired spins, they are not necessarily paramagnetic, because at ambient temperature quenching is very much the rule rather than the exception. The quenching tendency is weakest for f-electrons because f (especially 4f) orbitals are radially contracted and they overlap only weakly with orbitals on adjacent atoms. Consequently, the lanthanide elements with incompletely filled 4f-orbitals are paramagnetic or magnetically ordered.

μ_eff values for typical d³ and d⁵ transition metal complexes.

Material	μeff/μB
[Cr(NH3)6]Br3	3.77
K3[Cr(CN)6]	3.87
K3[MoCl6]	3.79
K4[V(CN)6]	3.78
[Mn(NH3)6]Cl2	5.92
(NH4)2[Mn(SO4)2]·6H2O	5.92
NH4[Fe(SO4)2]·12H2O	5.89

Thus, condensed phase paramagnets are only possible if the interactions of the spins that lead either to quenching or to ordering are kept at bay by structural isolation of the magnetic centers. There are two classes of materials for which this holds:

• Molecular materials with a (isolated) paramagnetic center.
  • Good examples are coordination complexes of d- or f-metals or proteins with such centers, e.g. myoglobin. In such materials the organic part of the molecule acts as an envelope shielding the spins from their neighbors.
  • Small molecules can be stable in radical form, oxygen O₂ is a good example. Such systems are quite rare because they tend to be rather reactive.
• Dilute systems.
  • Dissolving a paramagnetic species in a diamagnetic lattice at small concentrations, e.g. Nd³⁺ in CaCl₂ will separate the neodymium ions at large enough distances that they do not interact. Such systems are of prime importance for what can be considered the most sensitive method to study paramagnetic systems: EPR.

Systems with interactions

Idealized Curie–Weiss behavior; N.B. T_C=θ, but T_N is not θ. Paramagnetic regimes are denoted by solid lines. Close to T_N or T_C the behavior usually deviates from ideal.

As stated above, many materials that contain d- or f-elements do retain unquenched spins. Salts of such elements often show paramagnetic behavior but at low enough temperatures the magnetic moments may order. It is not uncommon to call such materials 'paramagnets', when referring to their paramagnetic behavior above their Curie or Néel-points, particularly if such temperatures are very low or have never been properly measured. Even for iron it is not uncommon to say that iron becomes a paramagnet above its relatively high Curie-point. In that case the Curie-point is seen as a phase transition between a ferromagnet and a 'paramagnet'. The word paramagnet now merely refers to the linear response of the system to an applied field, the temperature dependence of which requires an amended version of Curie's law, known as the Curie–Weiss law:

${\displaystyle \mathbf{M}=\frac{C}{T-\theta }\mathbf{H}}$

This amended law includes a term θ that describes the exchange interaction that is present albeit overcome by thermal motion. The sign of θ depends on whether ferro- or antiferromagnetic interactions dominate and it is seldom exactly zero, except in the dilute, isolated cases mentioned above.

Obviously, the paramagnetic Curie–Weiss description above T_N or T_C is a rather different interpretation of the word "paramagnet" as it does not imply the absence of interactions, but rather that the magnetic structure is random in the absence of an external field at these sufficiently high temperatures. Even if θ is close to zero this does not mean that there are no interactions, just that the aligning ferro- and the anti-aligning antiferromagnetic ones cancel. An additional complication is that the interactions are often different in different directions of the crystalline lattice (anisotropy), leading to complicated magnetic structures once ordered.

Randomness of the structure also applies to the many metals that show a net paramagnetic response over a broad temperature range. They do not follow a Curie type law as function of temperature however; often they are more or less temperature independent. This type of behavior is of an itinerant nature and better called Pauli-paramagnetism, but it is not unusual to see, for example, the metal aluminium called a "paramagnet", even though interactions are strong enough to give this element very good electrical conductivity.

Superparamagnets

Some materials show induced magnetic behavior that follows a Curie type law but with exceptionally large values for the Curie constants. These materials are known as superparamagnets. They are characterized by a strong ferromagnetic or ferrimagnetic type of coupling into domains of a limited size that behave independently from one another. The bulk properties of such a system resembles that of a paramagnet, but on a microscopic level they are ordered. The materials do show an ordering temperature above which the behavior reverts to ordinary paramagnetism (with interaction). Ferrofluids are a good example, but the phenomenon can also occur inside solids, e.g., when dilute paramagnetic centers are introduced in a strong itinerant medium of ferromagnetic coupling such as when Fe is substituted in TlCu₂Se₂ or the alloy AuFe. Such systems contain ferromagnetically coupled clusters that freeze out at lower temperatures. They are also called mictomagnets.

Linguistics

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Linguistics

Linguistics is the scientific study of language. The areas of linguistic analysis are syntax (rules governing the structure of sentences), semantics (meaning), morphology (structure of words), phonetics (speech sounds and equivalent gestures in sign languages), phonology (the abstract sound system of a particular language, and analogous systems of sign languages), and pragmatics (how the context of use contributes to meaning). Subdisciplines such as biolinguistics (the study of the biological variables and evolution of language) and psycholinguistics (the study of psychological factors in human language) bridge many of these divisions.

Linguistics encompasses many branches and subfields that span both theoretical and practical applications. Theoretical linguistics is concerned with understanding the universal and fundamental nature of language and developing a general theoretical framework for describing it. Applied linguistics seeks to utilize the scientific findings of the study of language for practical purposes, such as developing methods of improving language education and literacy.

Linguistic features may be studied through a variety of perspectives: synchronically (by describing the structure of a language at a specific point in time) or diachronically (through the historical development of a language over a period of time), in monolinguals or in multilinguals, among children or among adults, in terms of how it is being learnt or how it was acquired, as abstract objects or as cognitive structures, through written texts or through oral elicitation, and finally through mechanical data collection or practical fieldwork.

Linguistics emerged from the field of philology, of which some branches are more qualitative and holistic in approach. Today, philology and linguistics are variably described as related fields, subdisciplines, or separate fields of language study but, by and large, linguistics can be seen as an umbrella term. Linguistics is also related to the philosophy of language, stylistics, rhetoric, semiotics, lexicography, and translation.

Major subdisciplines

Swiss linguist Ferdinand de Saussure is regarded as the creator of semiotics

Historical linguistics

Main article: Historical linguistics

Historical linguistics is the study of how language changes over history, particularly with regard to a specific language or a group of languages. Western trends in historical linguistics date back to roughly the late 18th century, when the discipline grew out of philology, the study of ancient texts and oral traditions.

Historical linguistics emerged as one of the first few sub-disciplines in the field, and was most widely practised during the late 19th century. Despite a shift in focus in the 20th century towards formalism and generative grammar, which studies the universal properties of language, historical research today still remains a significant field of linguistic inquiry. Subfields of the discipline include language change and grammaticalization.

Historical linguistics studies language change either diachronically (through a comparison of different time periods in the past and present) or in a synchronic manner (by observing developments between different variations that exist within the current linguistic stage of a language).

At first, historical linguistics was the cornerstone of comparative linguistics, which involves a study of the relationship between different languages. At that time, scholars of historical linguistics were only concerned with creating different categories of language families, and reconstructing prehistoric proto-languages by using both the comparative method and the method of internal reconstruction. Internal reconstruction is the method by which an element that contains a certain meaning is re-used in different contexts or environments where there is a variation in either sound or analogy.

The reason for this had been to describe well-known Indo-European languages, many of which had detailed documentation and long written histories. Scholars of historical linguistics also studied Uralic languages, another European language family for which very little written material existed back then. After that, there also followed significant work on the corpora of other languages, such as the Austronesian languages and the Native American language families.

In historical work, the uniformitarian principle is generally the underlying working hypothesis, occasionally also clearly expressed. The principle was expressed early by William Dwight Whitney, who considered it imperative, a "must", of historical linguistics to "look to find the same principle operative also in the very outset of that [language] history."

The above approach of comparativism in linguistics is now, however, only a small part of the much broader discipline called historical linguistics. The comparative study of specific Indo-European languages is considered a highly specialized field today, while comparative research is carried out over the subsequent internal developments in a language: in particular, over the development of modern standard varieties of languages, and over the development of a language from its standardized form to its varieties.

For instance, some scholars also tried to establish super-families, linking, for example, Indo-European, Uralic, and other language families to a hypothetical Nostratic language group. While these attempts are still not widely accepted as credible methods, they provide necessary information to establish relatedness in language change. This is generally hard to find for events long ago, due to the occurrence of chance word resemblances and variations between language groups. A limit of around 10,000 years is often assumed for the functional purpose of conducting research. It is also hard to date various proto-languages. Even though several methods are available, these languages can be dated only approximately.

In modern historical linguistics, we examine how languages change over time, focusing on the relationships between dialects within a specific period. This includes studying morphological, syntactical, and phonetic shifts. Connections between dialects in the past and present are also explored.

Syntax

Main article: Syntax

Syntax is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, constituency, agreement, the nature of crosslinguistic variation, and the relationship between form and meaning. There are numerous approaches to syntax that differ in their central assumptions and goals.

Morphology

Main article: Morphology (linguistics)

Morphology is the study of words, including the principles by which they are formed, and how they relate to one another within a language. Most approaches to morphology investigate the structure of words in terms of morphemes, which are the smallest units in a language with some independent meaning. Morphemes include roots that can exist as words by themselves, but also categories such as affixes that can only appear as part of a larger word. For example, in English the root catch and the suffix -ing are both morphemes; catch may appear as its own word, or it may be combined with -ing to form the new word catching. Morphology also analyzes how words behave as parts of speech, and how they may be inflected to express grammatical categories including number, tense, and aspect. Concepts such as productivity are concerned with how speakers create words in specific contexts, which evolves over the history of a language.

The discipline that deals specifically with the sound changes occurring within morphemes is morphophonology.

Semantics and pragmatics

Main articles: Semantics and Pragmatics

Semantics and pragmatics are branches of linguistics concerned with meaning. These subfields have traditionally been divided according to aspects of meaning: "semantics" refers to grammatical and lexical meanings, while "pragmatics" is concerned with meaning in context. Within linguistics, the subfield of formal semantics studies the denotations of sentences and how they are composed from the meanings of their constituent expressions. Formal semantics draws heavily on philosophy of language and uses formal tools from logic and computer science. On the other hand, cognitive semantics explains linguistic meaning via aspects of general cognition, drawing on ideas from cognitive science such as prototype theory.

Pragmatics focuses on phenomena such as speech acts, implicature, and talk in interaction. Unlike semantics, which examines meaning that is conventional or "coded" in a given language, pragmatics studies how the transmission of meaning depends not only on the structural and linguistic knowledge (grammar, lexicon, etc.) of the speaker and listener, but also on the context of the utterance, any pre-existing knowledge about those involved, the inferred intent of the speaker, and other factors.

Phonetics and phonology

Main articles: Phonetics and Phonology

Phonetics and phonology are branches of linguistics concerned with sounds (or the equivalent aspects of sign languages). Phonetics is largely concerned with the physical aspects of sounds such as their articulation, acoustics, production, and perception. Phonology is concerned with the linguistic abstractions and categorizations of sounds, and it tells us what sounds are in a language, how they do and can combine into words, and explains why certain phonetic features are important to identifying a word.

Typology

Linguistic typology (or language typology) is a field of linguistics that studies and classifies languages according to their structural features to allow their comparison. Its aim is to describe and explain the structural diversity and the common properties of the world's languages. Its subdisciplines include, but are not limited to phonological typology, which deals with sound features; syntactic typology, which deals with word order and form; lexical typology, which deals with language vocabulary; and theoretical typology, which aims to explain the universal tendencies.

Structures

Linguistic structures are pairings of meaning and form. Any particular pairing of meaning and form is a Saussurean linguistic sign. For instance, the meaning "cat" is represented worldwide with a wide variety of different sound patterns (in oral languages), movements of the hands and face (in sign languages), and written symbols (in written languages). Linguistic patterns have proven their importance for the knowledge engineering field especially with the ever-increasing amount of available data.

Linguists focusing on structure attempt to understand the rules regarding language use that native speakers know (not always consciously). All linguistic structures can be broken down into component parts that are combined according to (sub)conscious rules, over multiple levels of analysis. For instance, consider the structure of the word "tenth" on two different levels of analysis. On the level of internal word structure (known as morphology), the word "tenth" is made up of one linguistic form indicating a number and another form indicating ordinality. The rule governing the combination of these forms ensures that the ordinality marker "th" follows the number "ten." On the level of sound structure (known as phonology), structural analysis shows that the "n" sound in "tenth" is made differently from the "n" sound in "ten" spoken alone. Although most speakers of English are consciously aware of the rules governing internal structure of the word pieces of "tenth", they are less often aware of the rule governing its sound structure. Linguists focused on structure find and analyze rules such as these, which govern how native speakers use language.

Grammar

Grammar is a system of rules which governs the production and use of utterances in a given language. These rules apply to sound as well as meaning, and include componential subsets of rules, such as those pertaining to phonology (the organization of phonetic sound systems), morphology (the formation and composition of words), and syntax (the formation and composition of phrases and sentences). Modern frameworks that deal with the principles of grammar include structural and functional linguistics, and generative linguistics.

Sub-fields that focus on a grammatical study of language include the following:

• Phonetics, the study of the physical properties of speech sound production and perception, and delves into their acoustic and articulatory properties
• Phonology, the study of sounds as abstract elements in the speaker's mind that distinguish meaning (phonemes)
• Morphology, the study of morphemes, or the internal structures of words and how they can be modified
• Syntax, the study of how words combine to form grammatical phrases and sentences
• Semantics, the study of lexical and grammatical aspects of meaning
• Pragmatics, the study of how utterances are used in communicative acts, and the role played by situational context and non-linguistic knowledge in the transmission of meaning
• Discourse analysis, the analysis of language use in texts (spoken, written, or signed)
• Stylistics, the study of linguistic factors (rhetoric, diction, stress) that place a discourse in context
• Semiotics, the study of signs and sign processes (semiosis), indication, designation, likeness, analogy, metaphor, symbolism, signification, and communication

Discourse

Discourse is language as social practice (Baynham, 1995) and is a multilayered concept. As a social practice, discourse embodies different ideologies through written and spoken texts. Discourse analysis can examine or expose these ideologies. Discourse not only influences genre, which is selected based on specific contexts but also, at a micro level, shapes language as text (spoken or written) down to the phonological and lexico-grammatical levels. Grammar and discourse are linked as parts of a system. A particular discourse becomes a language variety when it is used in this way for a particular purpose, and is referred to as a register. There may be certain lexical additions (new words) that are brought into play because of the expertise of the community of people within a certain domain of specialization. Thus, registers and discourses distinguish themselves not only through specialized vocabulary but also, in some cases, through distinct stylistic choices. People in the medical fraternity, for example, may use some medical terminology in their communication that is specialized to the field of medicine. This is often referred to as being part of the "medical discourse", and so on.

Lexicon

The lexicon is a catalogue of words and terms that are stored in a speaker's mind. The lexicon consists of words and bound morphemes, which are parts of words that can not stand alone, like affixes. In some analyses, compound words and certain classes of idiomatic expressions and other collocations are also considered to be part of the lexicon. Dictionaries represent attempts at listing, in alphabetical order, the lexicon of a given language; usually, however, bound morphemes are not included. Lexicography, closely linked with the domain of semantics, is the science of mapping the words into an encyclopedia or a dictionary. The creation and addition of new words (into the lexicon) is called coining or neologization, and the new words are called neologisms.

It is often believed that a speaker's capacity for language lies in the quantity of words stored in the lexicon. However, this is often considered a myth by linguists. The capacity for the use of language is considered by many linguists to lie primarily in the domain of grammar, and to be linked with competence, rather than with the growth of vocabulary. Even a very small lexicon is theoretically capable of producing an infinite number of sentences.

Vocabulary size is relevant as a measure of comprehension. There is general consensus that reading comprehension of a written text in English requires 98% coverage, meaning that the person understands 98% of the words in the text. The question of how much vocabulary is needed is therefore related to which texts or conversations need to be understood. A common estimate is 6-7,000 word families to understand a wide range of conversations and 8-9,000 word families to be able to read a wide range of written texts.

Style

Stylistics also involves the study of written, signed, or spoken discourse through varying speech communities, genres, and editorial or narrative formats in the mass media. It involves the study and interpretation of texts for aspects of their linguistic and tonal style. Stylistic analysis entails the analysis of description of particular dialects and registers used by speech communities. Stylistic features include rhetoric, diction, stress, satire, irony, dialogue, and other forms of phonetic variations. Stylistic analysis can also include the study of language in canonical works of literature, popular fiction, news, advertisements, and other forms of communication in popular culture as well. It is usually seen as a variation in communication that changes from speaker to speaker and community to community. In short, Stylistics is the interpretation of text.

In the 1960s, Jacques Derrida, for instance, further distinguished between speech and writing, by proposing that written language be studied as a linguistic medium of communication in itself. Palaeography is therefore the discipline that studies the evolution of written scripts (as signs and symbols) in language. The formal study of language also led to the growth of fields like psycholinguistics, which explores the representation and function of language in the mind; neurolinguistics, which studies language processing in the brain; biolinguistics, which studies the biology and evolution of language; and language acquisition, which investigates how children and adults acquire the knowledge of one or more languages.

Approaches

See also: Theory of language

Humanistic

The fundamental principle of humanistic linguistics, especially rational and logical grammar, is that language is an invention created by people. A semiotic tradition of linguistic research considers language a sign system which arises from the interaction of meaning and form. The organization of linguistic levels is considered computational. Linguistics is essentially seen as relating to social and cultural studies because different languages are shaped in social interaction by the speech community. Frameworks representing the humanistic view of language include structural linguistics, among others.

Structural analysis means dissecting each linguistic level: phonetic, morphological, syntactic, and discourse, to the smallest units. These are collected into inventories (e.g. phoneme, morpheme, lexical classes, phrase types) to study their interconnectedness within a hierarchy of structures and layers. Functional analysis adds to structural analysis the assignment of semantic and other functional roles that each unit may have. For example, a noun phrase may function as the subject or object of the sentence; or the agent or patient.

Functional linguistics, or functional grammar, is a branch of structural linguistics. In the humanistic reference, the terms structuralism and functionalism are related to their meaning in other human sciences. The difference between formal and functional structuralism lies in the way that the two approaches explain why languages have the properties they have. Functional explanation entails the idea that language is a tool for communication, or that communication is the primary function of language. Linguistic forms are consequently explained by an appeal to their functional value, or usefulness. Other structuralist approaches take the perspective that form follows from the inner mechanisms of the bilateral and multilayered language system.

Biological

Further information: Biolinguistics and Biosemiotics

Approaches such as cognitive linguistics and generative grammar study linguistic cognition with a view towards uncovering the biological underpinnings of language. In Generative Grammar, these underpinning are understood as including innate domain-specific grammatical knowledge. Thus, one of the central concerns of the approach is to discover what aspects of linguistic knowledge are innate and which are not.

Cognitive linguistics, in contrast, rejects the notion of innate grammar, and studies how the human mind creates linguistic constructions from event schemas, and the impact of cognitive constraints and biases on human language. In cognitive linguistics, language is approached via the senses.

A closely related approach is evolutionary linguistics which includes the study of linguistic units as cultural replicators. It is possible to study how language replicates and adapts to the mind of the individual or the speech community. Construction grammar is a framework which applies the meme concept to the study of syntax.

The generative versus evolutionary approach are sometimes called formalism and functionalism, respectively. This reference is however different from the use of the terms in human sciences.

Methodology

Modern linguistics is primarily descriptive. Linguists describe and explain features of language without making subjective judgments on whether a particular feature or usage is "good" or "bad". This is analogous to practice in other sciences: a zoologist studies the animal kingdom without making subjective judgments on whether a particular species is "better" or "worse" than another.

Prescription, on the other hand, is an attempt to promote particular linguistic usages over others, often favoring a particular dialect or "acrolect". This may have the aim of establishing a linguistic standard, which can aid communication over large geographical areas. It may also, however, be an attempt by speakers of one language or dialect to exert influence over speakers of other languages or dialects (see Linguistic imperialism). An extreme version of prescriptivism can be found among censors, who attempt to eradicate words and structures that they consider to be destructive to society. Prescription, however, may be practised appropriately in language instruction, like in ELT, where certain fundamental grammatical rules and lexical items need to be introduced to a second-language speaker who is attempting to acquire the language.

Sources

Most contemporary linguists work under the assumption that spoken data and signed data are more fundamental than written data. This is because

• Speech appears to be universal to all human beings capable of producing and perceiving it, while there have been many cultures and speech communities that lack written communication;
• Features appear in speech which are not always recorded in writing, including phonological rules, sound changes, and speech errors;
• All natural writing systems reflect a spoken language (or potentially a signed one), even with pictographic scripts like Dongba writing Naxi homophones with the same pictogram, and text in writing systems used for two languages changing to fit the spoken language being recorded;
• Speech evolved before human beings invented writing;
• Individuals learn to speak and process spoken language more easily and earlier than they do with writing.

Nonetheless, linguists agree that the study of written language can be worthwhile and valuable. For research that relies on corpus linguistics and computational linguistics, written language is often much more convenient for processing large amounts of linguistic data. Large corpora of spoken language are difficult to create and hard to find, and are typically transcribed and written. In addition, linguists have turned to text-based discourse occurring in various formats of computer-mediated communication as a viable site for linguistic inquiry.

The study of writing systems themselves, graphemics, is, in any case, considered a branch of linguistics.

Analysis

Before the 20th century, linguists analysed language on a diachronic plane, which was historical in focus. This meant that they would compare linguistic features and try to analyse language from the point of view of how it had changed between then and later. However, with the rise of Saussurean linguistics in the 20th century, the focus shifted to a more synchronic approach, where the study was geared towards analysis and comparison between different language variations, which existed at the same given point of time.

At another level, the syntagmatic plane of linguistic analysis entails the comparison between the way words are sequenced, within the syntax of a sentence. For example, the article "the" is followed by a noun, because of the syntagmatic relation between the words. The paradigmatic plane, on the other hand, focuses on an analysis that is based on the paradigms or concepts that are embedded in a given text. In this case, words of the same type or class may be replaced in the text with each other to achieve the same conceptual understanding.

History

Main article: History of linguistics

The earliest activities in the description of language have been attributed to the 6th-century-BC Indian grammarian Pāṇini who wrote a formal description of the Sanskrit language in his Aṣṭādhyāyī. Today, modern-day theories on grammar employ many of the principles that were laid down then.

Nomenclature

Before the 20th century, the term philology, first attested in 1716, was commonly used to refer to the study of language, which was then predominantly historical in focus. Since Ferdinand de Saussure's insistence on the importance of synchronic analysis, however, this focus has shifted and the term philology is now generally used for the "study of a language's grammar, history, and literary tradition", especially in the United States (where philology has never been very popularly considered as the "science of language").

Although the term linguist in the sense of "a student of language" dates from 1641, the term linguistics is first attested in 1847. It is now the usual term in English for the scientific study of language, though linguistic science is sometimes used.

Linguistics is a multi-disciplinary field of research that combines tools from natural sciences, social sciences, formal sciences, and the humanities. Many linguists, such as David Crystal, conceptualize the field as being primarily scientific. The term linguist applies to someone who studies language or is a researcher within the field, or to someone who uses the tools of the discipline to describe and analyse specific languages.

Early grammarians

Further information: Philology and Grammarian (Greco-Roman)

An early formal study of language was in India with Pāṇini, the 6th century BC grammarian who formulated 3,959 rules of Sanskrit morphology. Pāṇini's systematic classification of the sounds of Sanskrit into consonants and vowels, and word classes, such as nouns and verbs, was the first known instance of its kind. In the Middle East, Sibawayh, a Persian, made a detailed description of Arabic in AD 760 in his monumental work, Al-kitab fii an-naħw (الكتاب في النحو, The Book on Grammar), the first known author to distinguish between sounds and phonemes (sounds as units of a linguistic system). Western interest in the study of languages began somewhat later than in the East, but the grammarians of the classical languages did not use the same methods or reach the same conclusions as their contemporaries in the Indic world. Early interest in language in the West was a part of philosophy, not of grammatical description. The first insights into semantic theory were made by Plato in his Cratylus dialogue, where he argues that words denote concepts that are eternal and exist in the world of ideas. This work is the first to use the word etymology to describe the history of a word's meaning. Around 280 BC, one of Alexander the Great's successors founded a university (see Musaeum) in Alexandria, where a school of philologists studied the ancient texts in Greek, and taught Greek to speakers of other languages. While this school was the first to use the word "grammar" in its modern sense, Plato had used the word in its original meaning as "téchnē grammatikḗ" (Τέχνη Γραμματική), the "art of writing", which is also the title of one of the most important works of the Alexandrine school by Dionysius Thrax. Throughout the Middle Ages, the study of language was subsumed under the topic of philology, the study of ancient languages and texts, practised by such educators as Roger Ascham, Wolfgang Ratke, and John Amos Comenius.

Comparative philology

In the 18th century, the first use of the comparative method by William Jones sparked the rise of comparative linguistics. Bloomfield attributes "the first great scientific linguistic work of the world" to Jacob Grimm, who wrote Deutsche Grammatik. It was soon followed by other authors writing similar comparative studies on other language groups of Europe. The study of language was broadened from Indo-European to language in general by Wilhelm von Humboldt, of whom Bloomfield asserts:

This study received its foundation at the hands of the Prussian statesman and scholar Wilhelm von Humboldt (1767–1835), especially in the first volume of his work on Kavi, the literary language of Java, entitled Über die Verschiedenheit des menschlichen Sprachbaues und ihren Einfluß auf die geistige Entwickelung des Menschengeschlechts (On the Variety of the Structure of Human Language and its Influence upon the Mental Development of the Human Race).

20th-century developments

There was a shift of focus from historical and comparative linguistics to synchronic analysis in early 20th century. Structural analysis was improved by Leonard Bloomfield, Louis Hjelmslev; and Zellig Harris who also developed methods of discourse analysis. Functional analysis was developed by the Prague linguistic circle and André Martinet. As sound recording devices became commonplace in the 1960s, dialectal recordings were made and archived, and the audio-lingual method provided a technological solution to foreign language learning. The 1960s also saw a new rise of comparative linguistics: the study of language universals in linguistic typology. Towards the end of the century the field of linguistics became divided into further areas of interest with the advent of language technology and digitalized corpora.

Areas of research

Sociolinguistics

Main article: Sociolinguistics

Sociolinguistics is the study of how language is shaped by social factors. This sub-discipline focuses on the synchronic approach of linguistics, and looks at how a language in general, or a set of languages, display variation and varieties at a given point in time. The study of language variation and the different varieties of language through dialects, registers, and idiolects can be tackled through a study of style, as well as through analysis of discourse. Sociolinguists research both style and discourse in language, as well as the theoretical factors that are at play between language and society.

Developmental linguistics

Main article: Developmental linguistics

Developmental linguistics is the study of the development of linguistic ability in individuals, particularly the acquisition of language in childhood. Some of the questions that developmental linguistics looks into are how children acquire different languages, how adults can acquire a second language, and what the process of language acquisition is.

Neurolinguistics

Main article: Neurolinguistics

Neurolinguistics is the study of the structures in the human brain that underlie grammar and communication. Researchers are drawn to the field from a variety of backgrounds, bringing along a variety of experimental techniques as well as widely varying theoretical perspectives. Much work in neurolinguistics is informed by models in psycholinguistics and theoretical linguistics, and is focused on investigating how the brain can implement the processes that theoretical and psycholinguistics propose are necessary in producing and comprehending language. Neurolinguists study the physiological mechanisms by which the brain processes information related to language, and evaluate linguistic and psycholinguistic theories, using aphasiology, brain imaging, electrophysiology, and computer modelling. Amongst the structures of the brain involved in the mechanisms of neurolinguistics, the cerebellum which contains the highest numbers of neurons has a major role in terms of predictions required to produce language.

Applied linguistics

Main article: Applied linguistics

Linguists are largely concerned with finding and describing the generalities and varieties both within particular languages and among all languages. Applied linguistics takes the results of those findings and "applies" them to other areas. Linguistic research is commonly applied to areas such as language education, lexicography, translation, language planning, which involves governmental policy implementation related to language use, and natural language processing. "Applied linguistics" has been argued to be something of a misnomer. Applied linguists actually focus on making sense of and engineering solutions for real-world linguistic problems, and not literally "applying" existing technical knowledge from linguistics. Moreover, they commonly apply technical knowledge from multiple sources, such as sociology (e.g., conversation analysis) and anthropology. (Constructed language fits under Applied linguistics.)

Today, computers are widely used in many areas of applied linguistics. Speech synthesis and speech recognition use phonetic and phonemic knowledge to provide voice interfaces to computers. Applications of computational linguistics in machine translation, computer-assisted translation, and natural language processing are areas of applied linguistics that have come to the forefront. Their influence has had an effect on theories of syntax and semantics, as modelling syntactic and semantic theories on computers constraints.

Linguistic analysis is a sub-discipline of applied linguistics used by many governments to verify the claimed nationality of people seeking asylum who do not hold the necessary documentation to prove their claim. This often takes the form of an interview by personnel in an immigration department. Depending on the country, this interview is conducted either in the asylum seeker's native language through an interpreter or in an international lingua franca like English. Australia uses the former method, while Germany employs the latter; the Netherlands uses either method depending on the languages involved. Tape recordings of the interview then undergo language analysis, which can be done either by private contractors or within a department of the government. In this analysis, linguistic features of the asylum seeker are used by analysts to make a determination about the speaker's nationality. The reported findings of the linguistic analysis can play a critical role in the government's decision on the refugee status of the asylum seeker.

Language documentation

Language documentation combines anthropological inquiry (into the history and culture of language) with linguistic inquiry, in order to describe languages and their grammars. Lexicography involves the documentation of words that form a vocabulary. Such a documentation of a linguistic vocabulary from a particular language is usually compiled in a dictionary. Computational linguistics is concerned with the statistical or rule-based modeling of natural language from a computational perspective. Specific knowledge of language is applied by speakers during the act of translation and interpretation, as well as in language education – the teaching of a second or foreign language. Policy makers work with governments to implement new plans in education and teaching which are based on linguistic research.

Since the inception of the discipline of linguistics, linguists have been concerned with describing and analysing previously undocumented languages. Starting with Franz Boas in the early 1900s, this became the main focus of American linguistics until the rise of formal linguistics in the mid-20th century. This focus on language documentation was partly motivated by a concern to document the rapidly disappearing languages of indigenous peoples. The ethnographic dimension of the Boasian approach to language description played a role in the development of disciplines such as sociolinguistics, anthropological linguistics, and linguistic anthropology, which investigate the relations between language, culture, and society.

The emphasis on linguistic description and documentation has also gained prominence outside North America, with the documentation of rapidly dying indigenous languages becoming a focus in some university programs in linguistics. Language description is a work-intensive endeavour, usually requiring years of field work in the language concerned, so as to equip the linguist to write a sufficiently accurate reference grammar. Further, the task of documentation requires the linguist to collect a substantial corpus in the language in question, consisting of texts and recordings, both sound and video, which can be stored in an accessible format within open repositories, and used for further research.

Translation

Main articles: Translation and Translation studies

The sub-field of translation includes the translation of written and spoken texts across media, from digital to print and spoken. To translate literally means to transmute the meaning from one language into another. Translators are often employed by organizations such as travel agencies and governmental embassies to facilitate communication between two speakers who do not know each other's language. Translators are also employed to work within computational linguistics setups like Google Translate, which is an automated program to translate words and phrases between any two or more given languages. Translation is also conducted by publishing houses, which convert works of writing from one language to another in order to reach varied audiences. Cross-national and cross-cultural survey research studies employ translation to collect comparable data among multilingual populations. Academic translators specialize in or are familiar with various other disciplines such as technology, science, law, economics, etc.

Clinical linguistics

Main article: Clinical linguistics

Clinical linguistics is the application of linguistic theory to the field of speech-language pathology. Speech language pathologists work on corrective measures to treat communication and swallowing disorders.

Computational linguistics

Main article: Computational linguistics

Computational linguistics is the study of linguistic issues in a way that is "computationally responsible", i.e., taking careful note of computational consideration of algorithmic specification and computational complexity, so that the linguistic theories devised can be shown to exhibit certain desirable computational properties and their implementations. Computational linguists also work on computer language and software development.

Evolutionary linguistics

Main article: Evolutionary linguistics

Evolutionary linguistics is a sociobiological approach to analyzing the emergence of the language faculty through human evolution, and also the application of evolutionary theory to the study of cultural evolution among different languages. It is also a study of the dispersal of various languages across the globe, through movements among ancient communities.

Forensic linguistics

Main article: Forensic linguistics

Forensic linguistics is the application of linguistic analysis to forensics. Forensic analysis investigates the style, language, lexical use, and other linguistic and grammatical features used in the legal context to provide evidence in courts of law. Forensic linguists have also used their expertise in the framework of criminal cases.

History of cancer

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/History_of_cancer

A tumor removed by surgery in 1689.

The history of cancer describes the development of the field of oncology and its role in the history of medicine. It also covers its role in the history of public health, of hospitals, and social and cultural history.

Early diagnosis

In 2016, a 1.7 million year old osteosarcoma was reported by Dr Edward John Odes (a doctoral student in Anatomical Sciences from the University of the Witwatersrand Medical School, South Africa) and colleagues, representing the oldest documented malignant hominin cancer.

The earliest known descriptions of cancer appear in several papyri from ancient Egypt. The Edwin Smith Papyrus was written around 1600 BC (possibly a fragmentary copy of a text from 2500 BC) and contains a description of cancer, as well as a procedure to remove breast tumours by cauterization, stating that the disease has no treatment. However, incidents of cancer were rare. In a study by the University of Manchester, only one case was found "in the investigation of hundreds of Egyptian mummies, with few references to cancer in literary evidence."

Hippocrates (c. 460 BC – c. 370 BC) described several kinds of cancer, referring to them by the term καρκινος (carcinos), the Greek word for 'crab' or 'crayfish', as well as carcinoma. This comes from the appearance of the cut surface of a solid malignant tumour, with "the veins stretched on all sides as the animal the crab has its feet, whence it derives its name". Since it was against Greek tradition to open the body, Hippocrates only described and made drawings of outwardly visible tumours on the skin, nose, and breasts. Treatment was based on the humour theory of four bodily fluids (black and yellow bile, blood, and phlegm). According to the patient's humour, treatment consisted of diet, blood-letting, and/or laxatives. Celsus (c. 25 BC – 50 AD) translated carcinos into cancer, the Latin word for crab or crayfish.

In the 2nd century AD, the Greek physician Galen used oncos (Greek for 'swelling') to describe all tumours, reserving Hippocrates' term carcinos for malignant tumours. Galen also used the suffix -oma to indicate cancerous lesions. It is from Galen's usage that we derive the modern word oncology.

Through the centuries it was discovered that cancer could occur anywhere in the body, but Hippocrates' humour-theory-based treatment remained popular until the 19th century.

16th–19th century

A surgical operation to remove a malignant tumor, 1817

In the 16th and 17th centuries, it became more acceptable for doctors to dissect bodies to discover the cause of death. The German professor Wilhelm Fabry believed that breast cancer was caused by a milk clot in a mammary duct. The Dutch professor Francois de la Boe Sylvius, a follower of Descartes, believed that all disease was the outcome of chemical processes, and that acidic lymph fluid was the cause of cancer. His contemporary Nicolaes Tulp believed that cancer was a poison that slowly spreads, and concluded that it was contagious. In the 1600s, cancer was vulgarly called "the wolf[e]".

The first cause of cancer was identified by British surgeon Percivall Pott, who discovered in 1775 that cancer of the scrotum was a common disease among chimney sweeps. The work of other individual physicians led to various insights, but when physicians started working together they could draw firmer conclusions.

With the widespread use of the microscope in the 18th century, it was discovered that the 'cancer poison' eventually spreads from the primary tumour through the lymph nodes to other sites ("metastasis"). This view of the disease was first formulated by the English surgeon Campbell De Morgan between 1871 and 1874. The use of surgery to treat cancer had poor results due to problems with hygiene. The renowned Scottish surgeon Alexander Monro saw only 2 breast tumour patients out of 60 surviving surgery for two years. In the 19th century, asepsis improved surgical hygiene and as the survival statistics went up, surgical removal of the tumour became the primary treatment for cancer. With the exception of William Coley who in the late 19th century felt that the rate of cure after surgery had been higher before asepsis (and who injected bacteria into tumours with mixed results), cancer treatment became dependent on the individual art of the surgeon at removing a tumour. The underlying cause of his results might be that infection stimulates the immune system to destroy left tumour cells. During the same period, the idea that the body was made up of various tissues, that in turn were made up of millions of cells, laid rest the ancient belief in humor theory on chemical imbalances in the body.

Mechanism

1938 American Society for the Control of Cancer poster.

The genetic basis of cancer was recognised in 1902 by the German zoologist Theodor Boveri, professor of zoology at Munich and later in Würzburg. He discovered a method to generate cells with multiple copies of the centrosome, a structure he discovered and named. He postulated that chromosomes were distinct and transmitted different inheritance factors. He suggested that mutations of the chromosomes could generate a cell with unlimited growth potential which could be passed on to its descendants. He proposed the existence of cell cycle checkpoints, tumour suppressor genes and oncogenes. He speculated that cancers might be caused or promoted by radiation, physical or chemical injuries, or by pathogenic microorganisms.

1938 poster identifying surgery, x-rays and radium as the proper treatments for cancer.

Therapies

When Marie Curie and Pierre Curie discovered radiation at the end of the 19th century, they stumbled upon the first effective non-surgical cancer treatment. With radiation also came the first signs of multi-disciplinary approaches to cancer treatment. The surgeon was no longer operating in isolation but worked together with hospital radiologists to help patients. The complications in communication this brought, along with the necessity of the patient's treatment in a hospital facility rather than at home, also created a parallel process of compiling patient data into hospital files, which in turn led to the first statistical patient studies.

The American Cancer Society was founded in 1913 by 15 physicians and businessmen in New York City under the name American Society for the Control of Cancer (ASCC). The current name was adopted in 1945.

A founding paper of cancer epidemiology was the work of Janet Lane-Claypon, who published a comparative study in 1926 of 500 breast cancer cases and 500 control patients of the same background and lifestyle for the British Ministry of Health. Her groundbreaking work on cancer epidemiology was carried on by Richard Doll and Austin Bradford Hill, who published "Lung Cancer and Other Causes of Death In Relation to Smoking. A Second Report on the Mortality of British Doctors" followed in 1956 (otherwise known as the British doctors study). Richard Doll left the London Medical Research Centre (MRC), to start the Oxford unit for Cancer epidemiology in 1968. With the use of computers, the unit was the first to compile large amounts of cancer data. Modern epidemiological methods are closely linked to current concepts of disease and public health policy. Over the past 50 years, great efforts have been spent on gathering data across medical practice, hospital, provincial, state, and even country boundaries to study the interdependence of environmental and cultural factors on cancer incidence.

Cancer patient treatment and studies were restricted to individual physicians' practices until World War II when medical research centres discovered that there were large international differences in disease incidence. This insight drove national public health bodies to enable the compilation of health data across practices and hospitals, a process found in many countries today. The Japanese medical community observed that the bone marrow of victims of the atomic bombings of Hiroshima and Nagasaki was completely destroyed. They concluded that diseased bone marrow could also be destroyed with radiation, and this led to the development of bone marrow transplants for leukemia. Since World War II, trends in cancer treatment are to improve on a micro-level the existing treatment methods, standardize them, and globalize them to find cures through epidemiology and international partnerships.

In 1968 Michael A. Epstein, Bert Achong, and Yvonne Barr identified the first human cancer virus, called the Epstein–Barr virus.

War on Cancer

Main article: War on cancer

The 'war' on cancer in the U.S. focused on the expansion of research on causes and cures. It began with the National Cancer Act of 1971 The act was intended "to amend the Public Health Service Act so as to strengthen the National Cancer Institute in order to more effectively carry out the national effort against cancer". It was signed into law by then President Richard Nixon on December 23, 1971.

In 1973, cancer research led to a Cold War incident, where co-operative samples of reported oncoviruses were discovered to be contaminated by HeLa.

In 1984, Harald zur Hausen discovered first HPV16 and then HPV18 responsible for approximately 70% of cervical cancers. For discovery that human papillomaviruses (HPV) cause human cancer, zur Hausen won a 2008 Nobel Prize.

From 1971 to 2007 the United States invested over $200 billion on cancer research; that total includes funding from public and private sectors and foundations.

Despite this substantial investment, the country saw just a five percent decrease in the cancer death rate (adjusting for size and age of the population) between 1950 and 2005. Longer life expectancy may be a contributing factor to this, as cancer rates and mortality rates increase significantly with age. More than three out of five cancers are diagnosed in people aged 65 and over.