John Locke (updated)

From Wikipedia, the free encyclopedia

John Locke
Portrait of Locke in 1697 by Godfrey Kneller
Born	29 August 1632 Wrington, Somerset, England
Died	28 October 1704 (aged 72) High Laver, Essex, England
Nationality	English
Education	Christ Church, Oxford
Era	17th-century philosophy (Early modern philosophy)
Region	Western philosophy
School	Empiricism Foundationalism Conceptualism Indirect realism Correspondence theory of truth Ideational theory of meaning Corpuscularianism Social contract Natural law Liberalism
Main interests	Metaphysics, epistemology, political philosophy, philosophy of mind, philosophy of education, economics
Notable ideas	Consciousness Consent of the governed Labor theory of property Law of opinion Lockean proviso Molyneux's problem Natural rights (rights of life, liberty and property) Primary/secondary quality distinction Social contract State of nature Tabula rasa
Signature

John Locke's kit-cat portrait by Godfrey Kneller, National Portrait Gallery, London

 

John Locke FRS (/lɒk/; 29 August 1632 – 28 October 1704) was an English philosopher and physician, widely regarded as one of the most influential of Enlightenment thinkers and commonly known as the "Father of Liberalism". Considered one of the first of the British empiricists, following the tradition of Sir Francis Bacon, he is equally important to social contract theory. His work greatly affected the development of epistemology and political philosophy. His writings influenced Voltaire and Jean-Jacques Rousseau, many Scottish Enlightenment thinkers, as well as the American revolutionaries. His contributions to classical republicanism and liberal theory are reflected in the United States Declaration of Independence.

Locke's theory of mind is often cited as the origin of modern conceptions of identity and the self, figuring prominently in the work of later philosophers such as David Hume, Rousseau, and Immanuel Kant. Locke was the first to define the self through a continuity of consciousness. He postulated that, at birth, the mind was a blank slate or tabula rasa. Contrary to Cartesian philosophy based on pre-existing concepts, he maintained that we are born without innate ideas, and that knowledge is instead determined only by experience derived from sense perception. This is now known as empiricism. An example of Locke's belief in empiricism can be seen in his quote, "whatever I write, as soon as I discover it not to be true, my hand shall be the forwardest to throw it into the fire." This shows the ideology of science in his observations in that something must be capable of being tested repeatedly and that nothing is exempt from being disproven. Challenging the work of others, Locke is said to have established the method of introspection, or observing the emotions and behaviours of one's self.

Life and work

Locke's father, also called John, was an attorney who served as clerk to the Justices of the Peace in Chew Magna; he had served as a captain of cavalry for the Parliamentarian forces during the early part of the English Civil War. His mother was Agnes Keene. Both parents were Puritans. Locke was born on 29 August 1632, in a small thatched cottage by the church in Wrington, Somerset, about 12 miles from Bristol. He was baptized the same day. Soon after Locke's birth, the family moved to the market town of Pensford, about seven miles south of Bristol, where Locke grew up in a rural Tudor house in Belluton. 

In 1647, Locke was sent to the prestigious Westminster School in London under the sponsorship of Alexander Popham, a member of Parliament and his father's former commander. After completing studies there, he was admitted to Christ Church, Oxford, in the autumn of 1652 at the age of twenty. The dean of the college at the time was John Owen, vice-chancellor of the university. Although a capable student, Locke was irritated by the undergraduate curriculum of the time. He found the works of modern philosophers, such as René Descartes, more interesting than the classical material taught at the university. Through his friend Richard Lower, whom he knew from the Westminster School, Locke was introduced to medicine and the experimental philosophy being pursued at other universities and in the Royal Society, of which he eventually became a member. 

Locke was awarded a bachelor's degree in February 1656 and a master's degree in June 1658. He obtained a bachelor of medicine in February 1675, having studied medicine extensively during his time at Oxford and worked with such noted scientists and thinkers as Robert Boyle, Thomas Willis, Robert Hooke and Richard Lower. In 1666, he met Lord Anthony Ashley Cooper, 1st Earl of Shaftesbury, who had come to Oxford seeking treatment for a liver infection. Cooper was impressed with Locke and persuaded him to become part of his retinue.

Locke had been looking for a career and in 1667 moved into Shaftesbury's home at Exeter House in London, to serve as Lord Ashley's personal physician. In London, Locke resumed his medical studies under the tutelage of Thomas Sydenham. Sydenham had a major effect on Locke's natural philosophical thinking – an effect that would become evident in An Essay Concerning Human Understanding.

 

Locke's medical knowledge was put to the test when Shaftesbury's liver infection became life-threatening. Locke coordinated the advice of several physicians and was probably instrumental in persuading Shaftesbury to undergo surgery (then life-threatening itself) to remove the cyst. Shaftesbury survived and prospered, crediting Locke with saving his life. 

During this time, Locke served as Secretary of the Board of Trade and Plantations and Secretary to the Lords Proprietor of Carolina, which helped to shape his ideas on international trade and economics. 

Shaftesbury, as a founder of the Whig movement, exerted great influence on Locke's political ideas. Locke became involved in politics when Shaftesbury became Lord Chancellor in 1672. Following Shaftesbury's fall from favor in 1675, Locke spent some time traveling across France as tutor and medical attendant to Caleb Banks. He returned to England in 1679 when Shaftesbury's political fortunes took a brief positive turn. Around this time, most likely at Shaftesbury's prompting, Locke composed the bulk of the Two Treatises of Government. While it was once thought that Locke wrote the Treatises to defend the Glorious Revolution of 1688, recent scholarship has shown that the work was composed well before this date. The work is now viewed as a more general argument against absolute monarchy (particularly as espoused by Robert Filmer and Thomas Hobbes) and for individual consent as the basis of political legitimacy. Although Locke was associated with the influential Whigs, his ideas about natural rights and government are today considered quite revolutionary for that period in English history. 

Locke fled to the Netherlands in 1683, under strong suspicion of involvement in the Rye House Plot, although there is little evidence to suggest that he was directly involved in the scheme. The philosopher and novelist Rebecca Newberger Goldstein argues that during his five years in Holland, Locke chose his friends "from among the same freethinking members of dissenting Protestant groups as Spinoza's small group of loyal confidants. [Baruch Spinoza had died in 1677.] Locke almost certainly met men in Amsterdam who spoke of the ideas of that renegade Jew who... insisted on identifying himself through his religion of reason alone." While she says that "Locke's strong empiricist tendencies" would have "disinclined him to read a grandly metaphysical work such as Spinoza's Ethics, in other ways he was deeply receptive to Spinoza's ideas, most particularly to the rationalist's well thought out argument for political and religious tolerance and the necessity of the separation of church and state."

In the Netherlands, Locke had time to return to his writing, spending a great deal of time re-working the Essay and composing the Letter on Toleration. Locke did not return home until after the Glorious Revolution. Locke accompanied Mary II back to England in 1688. The bulk of Locke's publishing took place upon his return from exile – his aforementioned Essay Concerning Human Understanding, the Two Treatises of Civil Government and A Letter Concerning Toleration all appearing in quick succession.

Locke's close friend Lady Masham invited him to join her at Otes, the Mashams' country house in Essex. Although his time there was marked by variable health from asthma attacks, he nevertheless became an intellectual hero of the Whigs. During this period he discussed matters with such figures as John Dryden and Isaac Newton.

He died on 28 October 1704, and is buried in the churchyard of the village of High Laver, east of Harlow in Essex, where he had lived in the household of Sir Francis Masham since 1691. Locke never married nor had children.

Events that happened during Locke's lifetime include the English Restoration, the Great Plague of London and the Great Fire of London. He did not quite see the Act of Union of 1707, though the thrones of England and Scotland were held in personal union throughout his lifetime. Constitutional monarchy and parliamentary democracy were in their infancy during Locke's time.

Ideas

In the late 17th and early 18th centuries, Locke's Two Treatises were rarely cited. Historian Julian Hoppit said of the book, "except among some Whigs, even as a contribution to the intense debate of the 1690s it made little impression and was generally ignored until 1703 (though in Oxford in 1695 it was reported to have made 'a great noise')". John Kenyon, in his study of British political debate from 1689 to 1720, has remarked that Locke's theories were "mentioned so rarely in the early stages of the [Glorious] Revolution, up to 1692, and even less thereafter, unless it was to heap abuse on them" and that "no one, including most Whigs, [were] ready for the idea of a notional or abstract contract of the kind adumbrated by Locke". In contrast, Kenyon adds that Algernon Sidney's Discourses Concerning Government were "certainly much more influential than Locke's Two Treatises".

John Locke

In the 50 years after Queen Anne's death in 1714, the Two Treatises were reprinted only once (except in the collected works of Locke). However, with the rise of American resistance to British taxation, the Second Treatise gained a new readership; it was frequently cited in the debates in both America and Britain. The first American printing occurred in 1773 in Boston.

Locke exercised a profound influence on political philosophy, in particular on modern liberalism. Michael Zuckert has argued that Locke launched liberalism by tempering Hobbesian absolutism and clearly separating the realms of Church and State. He had a strong influence on Voltaire who called him "le sage Locke". His arguments concerning liberty and the social contract later influenced the written works of Alexander Hamilton, James Madison, Thomas Jefferson, and other Founding Fathers of the United States. In fact, one passage from the Second Treatise is reproduced verbatim in the Declaration of Independence, the reference to a "long train of abuses". Such was Locke's influence that Thomas Jefferson wrote: "Bacon, Locke and Newton... I consider them as the three greatest men that have ever lived, without any exception, and as having laid the foundation of those superstructures which have been raised in the Physical and Moral sciences".

But Locke's influence may have been even more profound in the realm of epistemology. Locke redefined subjectivity, or self, and intellectual historians such as Charles Taylor and Jerrold Seigel argue that Locke's An Essay Concerning Human Understanding (1690) marks the beginning of the modern Western conception of the self.

Locke's theory of association heavily influenced the subject matter of modern psychology. At the time, the empiricist philosopher's recognition of two types of ideas, simple and complex ideas, more importantly their interaction through associationism inspired other philosophers, such as David Hume and George Berkeley, to revise and expand this theory and apply it to explain how humans gain knowledge in the physical world.

Theories of religious tolerance

John Locke by Richard Westmacott, University College, London

 

Locke, writing his Letters Concerning Toleration (1689–1692) in the aftermath of the European wars of religion, formulated a classic reasoning for religious tolerance. Three arguments are central: (1) Earthly judges, the state in particular, and human beings generally, cannot dependably evaluate the truth-claims of competing religious standpoints; (2) Even if they could, enforcing a single "true religion" would not have the desired effect, because belief cannot be compelled by violence; (3) Coercing religious uniformity would lead to more social disorder than allowing diversity.

With regard to his position on religious tolerance, Locke was influenced by Baptist theologians like John Smyth and Thomas Helwys, who had published tracts demanding freedom of conscience in the early 17th century. Baptist theologian Roger Williams founded the colony Rhode Island in 1636, where he combined a democratic constitution with unlimited religious freedom. His tract The Bloody Tenent of Persecution for Cause of Conscience (1644), which was widely read in the mother country, was a passionate plea for absolute religious freedom and the total separation of church and state. Freedom of conscience had had high priority on the theological, philosophical and political agenda, since Martin Luther refused to recant his beliefs before the Diet of the Holy Roman Empire at Worms in 1521, unless he would be proved false by the Bible.

Constitution of Carolina

Appraisals of Locke have often been tied to appraisals of liberalism in general, and to appraisals of the United States. Detractors note that (in 1671) he was a major investor in the English slave-trade through the Royal African Company. In addition, he participated in drafting the Fundamental Constitutions of Carolina while Shaftesbury's secretary, which established a feudal aristocracy and gave a master absolute power over his slaves. For example, Martin Cohen notes that Locke, as a secretary to the Council of Trade and Plantations (1673–1674) and a member of the Board of Trade (1696–1700), was in fact, "one of just half a dozen men who created and supervised both the colonies and their iniquitous systems of servitude". Some see his statements on unenclosed property as having been intended to justify the displacement of the Native Americans. Because of his opposition to aristocracy and slavery in his major writings, he is accused of hypocrisy and racism, or of caring only for the liberty of English capitalists. Locke also drafted implementing instructions for the Carolina colonists designed to ensure that settlement and development was consistent with the Fundamental Constitutions. Collectively, these documents are known as the Grand Model for the Province of Carolina.

Theory of value and property

Locke uses the word property in both broad and narrow senses. In a broad sense, it covers a wide range of human interests and aspirations; more narrowly, it refers to material goods. He argues that property is a natural right and it is derived from labor. In Chapter V of his Second Treatise, Locke argues that the individual ownership of goods and property is justified by the labor exerted to produce those goods or utilise property to produce goods beneficial to human society.

Locke stated his belief, in his Second Treatise, that nature on its own provides little of value to society, implying that the labour expended in the creation of goods gives them their value. This position can be seen as a labor theory of value. From this premise, Locke developed a labor theory of property, namely that ownership of property is created by the application of labor. In addition, he believed that property precedes government and government cannot "dispose of the estates of the subjects arbitrarily." Karl Marx later critiqued Locke's theory of property in his own social theory.

Political theory

Locke's political theory was founded on social contract theory. Unlike Thomas Hobbes, Locke believed that human nature is characterized by reason and tolerance. Like Hobbes, Locke believed that human nature allowed people to be selfish. This is apparent with the introduction of currency. In a natural state all people were equal and independent, and everyone had a natural right to defend his "life, health, liberty, or possessions". Most scholars trace the phrase "Life, Liberty and the pursuit of Happiness," in the American Declaration of Independence, to Locke's theory of rights, though other origins have been suggested.

Like Hobbes, Locke assumed that the sole right to defend in the state of nature was not enough, so people established a civil society to resolve conflicts in a civil way with help from government in a state of society. However, Locke never refers to Hobbes by name and may instead have been responding to other writers of the day. Locke also advocated governmental separation of powers and believed that revolution is not only a right but an obligation in some circumstances. These ideas would come to have profound influence on the Declaration of Independence and the Constitution of the United States.

Limits to accumulation

According to Locke, unused property is wasteful and an offense against nature, but, with the introduction of "durable" goods, men could exchange their excessive perishable goods for goods that would last longer and thus not offend the natural law. In his view, the introduction of money marks the culmination of this process, making possible the unlimited accumulation of property without causing waste through spoilage. He also includes gold or silver as money because they may be "hoarded up without injury to anyone," since they do not spoil or decay in the hands of the possessor. In his view, the introduction of money eliminates the limits of accumulation. Locke stresses that inequality has come about by tacit agreement on the use of money, not by the social contract establishing civil society or the law of land regulating property. Locke is aware of a problem posed by unlimited accumulation but does not consider it his task. He just implies that government would function to moderate the conflict between the unlimited accumulation of property and a more nearly equal distribution of wealth; he does not identify which principles that government should apply to solve this problem. However, not all elements of his thought form a consistent whole. For example, labour theory of value of the Two Treatises of Government stands side by side with the demand-and-supply theory developed in a letter he wrote titled Some Considerations on the Consequences of the Lowering of Interest and the Raising of the Value of Money. Moreover, Locke anchors property in labour but in the end upholds the unlimited accumulation of wealth.

On price theory

Locke's general theory of value and price is a supply and demand theory, which was set out in a letter to a Member of Parliament in 1691, titled Some Considerations on the Consequences of the Lowering of Interest and the Raising of the Value of Money. He refers to supply as "quantity" and demand as "rent". "The price of any commodity rises or falls by the proportion of the number of buyer and sellers," and "that which regulates the price... [of goods] is nothing else but their quantity in proportion to their rent." The quantity theory of money forms a special case of this general theory. His idea is based on "money answers all things" (Ecclesiastes) or "rent of money is always sufficient, or more than enough," and "varies very little..." Locke concludes that as far as money is concerned, the demand is exclusively regulated by its quantity, regardless of whether the demand for money is unlimited or constant. He also investigates the determinants of demand and supply. For supply, he explains the value of goods as based on their scarcity and ability to be exchanged and consumed. He explains demand for goods as based on their ability to yield a flow of income. Locke develops an early theory of capitalization, such as land, which has value because "by its constant production of saleable commodities it brings in a certain yearly income." He considers the demand for money as almost the same as demand for goods or land; it depends on whether money is wanted as medium of exchange. As a medium of exchange, he states that "money is capable by exchange to procure us the necessaries or conveniences of life," and for loanable funds, "it comes to be of the same nature with land by yielding a certain yearly income... or interest."

Monetary thoughts

Locke distinguishes two functions of money, as a "counter" to measure value, and as a "pledge" to lay claim to goods. He believes that silver and gold, as opposed to paper money, are the appropriate currency for international transactions. Silver and gold, he says, are treated to have equal value by all of humanity and can thus be treated as a pledge by anyone, while the value of paper money is only valid under the government which issues it. 

Locke argues that a country should seek a favorable balance of trade, lest it fall behind other countries and suffer a loss in its trade. Since the world money stock grows constantly, a country must constantly seek to enlarge its own stock. Locke develops his theory of foreign exchanges, in addition to commodity movements, there are also movements in country stock of money, and movements of capital determine exchange rates. He considers the latter less significant and less volatile than commodity movements. As for a country's money stock, if it is large relative to that of other countries, he says it will cause the country's exchange to rise above par, as an export balance would do. 

He also prepares estimates of the cash requirements for different economic groups (landholders, laborers and brokers). In each group he posits that the cash requirements are closely related to the length of the pay period. He argues the brokers – middlemen – whose activities enlarge the monetary circuit and whose profits eat into the earnings of laborers and landholders, have a negative influence on both personal and the public economy to which they supposedly contribute.

The self

Locke defines the self as "that conscious thinking thing, (whatever substance, made up of whether spiritual, or material, simple, or compounded, it matters not) which is sensible, or conscious of pleasure and pain, capable of happiness or misery, and so is concerned for itself, as far as that consciousness extends". He does not, however, ignore "substance", writing that "the body too goes to the making the man."

In his Essay, Locke explains the gradual unfolding of this conscious mind. Arguing against both the Augustinian view of man as originally sinful and the Cartesian position, which holds that man innately knows basic logical propositions, Locke posits an "empty" mind, a tabula rasa, which is shaped by experience; sensations and reflections being the two sources of all our ideas.

Locke's Some Thoughts Concerning Education is an outline on how to educate this mind: he expresses the belief that education maketh the man, or, more fundamentally, that the mind is an "empty cabinet", with the statement, "I think I may say that of all the men we meet with, nine parts of ten are what they are, good or evil, useful or not, by their education."

Locke also wrote that "the little and almost insensible impressions on our tender infancies have very important and lasting consequences." He argued that the "associations of ideas" that one makes when young are more important than those made later because they are the foundation of the self: they are, put differently, what first mark the tabula rasa. In his Essay, in which both these concepts are introduced, Locke warns against, for example, letting "a foolish maid" convince a child that "goblins and sprites" are associated with the night for "darkness shall ever afterwards bring with it those frightful ideas, and they shall be so joined, that he can no more bear the one than the other."

This theory came to be called "associationism", and it strongly influenced 18th-century thought, particularly educational theory, as nearly every educational writer warned parents not to allow their children to develop negative associations. It also led to the development of psychology and other new disciplines with David Hartley's attempt to discover a biological mechanism for associationism in his Observations on Man (1749).

Dream argument

Locke was critical of Descartes' version of the dream argument, with Locke making the counterargument that people cannot have physical pain in dreams as they do in waking life.

Religious beliefs

Some scholars have seen Locke's political convictions as being based from his religious beliefs. Locke's religious trajectory began in Calvinist trinitarianism, but by the time of the Reflections (1695) Locke was advocating not just Socinian views on tolerance but also Socinian Christology. However Wainwright (1987) notes that in the posthumously published Paraphrase (1707) Locke's interpretation of one verse, Ephesians 1:10, is markedly different from that of Socinians like Biddle, and may indicate that near the end of his life Locke returned nearer to an Arian position, thereby accepting Christ's pre-existence. Locke was at times not sure about the subject of original sin, so he was accused of Socinianism, Arianism, or Deism. But he did not deny the reality of evil. Man was capable of waging unjust wars and committing crimes. Criminals had to be punished, even with the death penalty. With regard to the Bible Locke was very conservative. He retained the doctrine of the verbal inspiration of the Scriptures. The miracles were proof of the divine nature of the biblical message. Locke was convinced that the entire content of the Bible was in agreement with human reason (The reasonableness of Christianity, 1695). Although Locke was an advocate of tolerance, he urged the authorities not to tolerate atheism, because he thought the denial of God's existence would undermine the social order and lead to chaos. That excluded all atheistic varieties of philosophy and all attempts to deduce ethics and natural law from purely secular premises. In Locke's opinion the cosmological argument was valid and proved God's existence. His political thought was based on Protestant Christian views.

Philosophy From Religion

Locke's concept of man started with the belief in creation. Like philosophers Hugo Grotius and Samuel Pufendorf, Locke equated natural law with the biblical revelation. Locke derived the fundamental concepts of his political theory from biblical texts, in particular from Genesis 1 and 2 (creation), the Decalogue, the Golden Rule, the teachings of Jesus, and the letters of Paul the Apostle. The Decalogue puts a person's life, their reputation, and property under God's protection. 

Locke's philosophy on freedom is also derived from the Bible. Locke also derived basic human equality from the Bible, including the equality of the sexes, the starting point of the theological doctrine of Imago Dei. To Locke, one of the consequences of the principle of equality was that all humans were created equally free and therefore governments needed the consent of the governed. Locke compared the English Monarchy's rule over the British people to Adam's rule over Eve in Genesis, which was appointed by God.

Following Locke's philosophy, the American Declaration of Independence founded human rights partially on the biblical belief in creation. Locke's doctrine that governments need the consent of the governed is also central to the Declaration of Independence.

List of major works

• A Letter Concerning Toleration, 1689.
  • (1690) A Second Letter Concerning Toleration
  • (1692) A Third Letter for Toleration
• (1689) Two Treatises of Government (published throughout the 18th century by London bookseller Andrew Millar by commission for Thomas Hollis)
• (1690) An Essay Concerning Human Understanding
• (1691) Some Considerations on the consequences of the Lowering of Interest and the Raising of the Value of Money
• (1693) Some Thoughts Concerning Education
• (1695) The Reasonableness of Christianity, as Delivered in the Scriptures
  • (1695) A Vindication of the Reasonableness of Christianity

Major posthumous manuscripts

• (1660) First Tract of Government (or the English Tract)
• (c.1662) Second Tract of Government (or the Latin Tract)
• (1664) Questions Concerning the Law of Nature (definitive Latin text, with facing accurate English trans. in Robert Horwitz et al., eds., John Locke, Questions Concerning the Law of Nature, Ithaca: Cornell University Press, 1990).
• (1667) Essay Concerning Toleration
• (1706) Of the Conduct of the Understanding
• (1707) A paraphrase and notes on the Epistles of St. Paul to the Galatians, 1 and 2 Corinthians, Romans, Ephesians

Biological aspects of fluorine

From Wikipedia, the free encyclopedia

 

PET scan using fluorine-18

 

Biological aspects of fluorine describes the effects of fluorine-containing compounds with life. Fluorine (F₂) itself is very rare in everyday life, but hundreds of fluorine-containing compounds occur as minerals, medicines, pesticides, and materials. Naturally occurring organofluorine compounds are extremely rare. Nonetheless, twenty percent of all commercialized pharmaceuticals contain fluorine, examples being Lipitor and Prozac.

Manmade fluorinated compounds have also played a role in several noteworthy environmental concerns. Chlorofluorocarbons, once major components of numerous commercial aerosol products, have proven damaging to Earth's ozone layer and resulted in the wide-reaching Montreal Protocol (though in truth the chlorine in CFCs is the destructive actor, fluorine is an important part of these molecules because it makes them very stable and long-lived). Similarly, the stability of many organofluorine compounds has raised the issue of biopersistence. Long-lived molecules from waterproofing sprays, for example PFOA and PFOS, are found worldwide in the tissues of wildlife and humans, including newborn children.

Fluorine biology is also relevant to a number of cutting-edge technologies. PFCs (perfluorocarbons) are capable of holding enough oxygen to support human liquid breathing. Organofluorine in the form of its radioisotope ¹⁸F is also at the heart of a modern medical imaging technique known as positron emission tomography (PET). A PET scan produces three-dimensional colored images of parts of the body that use a lot of sugar, particularly the brain or tumors.

Dental care

Since the mid-20th century, it has been discerned from population studies (though incompletely understood) that fluoride reduces tooth decay. Initially, researchers hypothesized that fluoride helped by converting tooth enamel from the more acid-soluble mineral hydroxyapatite to the less acid-soluble mineral fluorapatite. However, more recent studies showed no difference in the frequency of caries (cavities) among teeth that were pre-fluoridated to different degrees. Current thinking is that fluoride prevents cavities primarily by helping teeth that are in the very early stages of tooth decay.

Topical fluoride treatment in Panama

 

When teeth begin to decay from the acid of sugar-consuming bacteria, calcium is lost (demineralization). However, teeth have a limited ability to recover calcium if decay is not too far advanced (remineralization). Fluoride appears to reduce demineralization and increase remineralization. Also, there is some evidence that fluoride interferes with the bacteria that consume sugars in the mouth and make tooth-destroying acids. In any case, it is only the fluoride that is directly present in the mouth (topical treatment) that prevents cavities. Fluoride ions that are swallowed do not benefit the teeth.

Water fluoridation is the controlled addition of fluoride to a public water supply to reduce tooth decay. Its use began in the 1940s, following studies of children in a region where water is naturally fluoridated. It is now used for about two-thirds of the U.S. population on public water systems and for about 5.7% of people worldwide. Although the best available evidence shows no association with adverse effects other than fluorosis (dental and, in worse cases, skeletal), most of which is mild, water fluoridation has been contentious for ethical, safety, and efficacy reasons, and opposition to water fluoridation exists despite its support by public health organizations. The benefits of water fluoridation have lessened recently, presumably because of the availability of fluoride in other forms, but are still measurable, particularly for low income groups. Systematic reviews in 2000 and 2007 showed significant reduction of cavities in children associated with water fluoridation.

Sodium fluoride, tin difluoride, and, most commonly, sodium monofluorophosphate, are used in toothpaste. In 1955, the first fluoride toothpaste was introduced in the United States. Now, almost all toothpaste in developed countries is fluoridated. For example, 95% of European toothpaste contains fluoride. Gels and foams are often advised for special patient groups, particularly those undergoing radiation therapy to the head (cancer patients). The patient receives a four-minute application of a high amount of fluoride. Varnishes, which can be more quickly applied, exist and perform a similar function. Fluoride is also contained in prescription and non-prescription mouthwashes and is a trace component of foods manufactured using fluoridated water supplies.

Medical applications

Pharmaceuticals

Prozac: one of several notable fluorine-containing drugs

 

Of all commercialized pharmaceutical drugs, twenty percent contain fluorine, including important drugs in many different pharmaceutical classes. Fluorine is often added to drug molecules as even a single atom can greatly change the chemical properties of the molecule in desirable ways. 

Because of the considerable stability of the carbon-fluorine bond, many drugs are fluorinated to delay their metabolism, which is the chemical process in which the drugs are turned into compounds that allows them to be eliminated. This prolongs their half-lives and allows for longer times between dosing and activation. For example, an aromatic ring may prevent the metabolism of a drug, but this presents a safety problem, because some aromatic compounds are metabolized in the body into poisonous epoxides by the organism's native enzymes. Substituting a fluorine into a para position, however, protects the aromatic ring and prevents the epoxide from being produced.

Adding fluorine to biologically active organics increases their lipophilicity (ability to dissolve in fats), because the carbon–fluorine bond is even more hydrophobic than the carbon–hydrogen bond. This effect often increases a drug's bioavailability because of increased cell membrane penetration. Although the potential of fluorine being released in a fluoride leaving group depends on its position in the molecule, organofluorides are generally very stable, since the carbon–fluorine bond is strong.

Fluorines also find their uses in common mineralocorticoids, a class of drugs that increase the blood pressure. Adding a fluorine increases both its medical power and anti-inflammatory effects. Fluorine-containing fludrocortisone is one of the most common of these drugs. Dexamethasone and triamcinolone, which are among the most potent of the related synthetic corticosteroids class of drugs, contain fluorine as well.

Several inhaled general anesthetic agents, including the most commonly used inhaled agents, also contain fluorine. The first fluorinated anesthetic agent, halothane, proved to be much safer (neither explosive nor flammable) and longer-lasting than those previously used. Modern fluorinated anesthetics are longer-lasting still and almost insoluble in blood, which accelerates the awakening. Examples include sevoflurane, desflurane, enflurane, and isoflurane, all hydrofluorocarbon derivatives.

Prior to the 1980s, antidepressants altered not only serotonin uptake (lack of serotonin is a reason for a depression), but also the uptake of altered norepinephrine; the latter caused most of the side effects of antidepressants. The first drug to alter only the serotonin uptake was Prozac; it gave birth to the extensive selective serotonin reuptake inhibitor (SSRI) antidepressant class and is the best-selling antidepressant. Many other SSRI antidepressants are fluorinated organics, including Celexa, Luvox, and Lexapro. Fluoroquinolones are a commonly used family of broad-spectrum antibiotics.

Scanning

PET scan for diagnosis of Alzheimer's disease

 

Compounds containing fluorine-18, a radioactive isotope that emits positrons, are often used in positron emission tomography (PET) scanning, because the isotope's half-life of about 110 minutes is usefully long by positron-emitter standards. One such radiopharmaceutical is 2-deoxy-2-(¹⁸F)fluoro-D-glucose (generically referred to as fludeoxyglucose), commonly abbreviated as ¹⁸F-FDG, or simply FDG. In PET imaging, FDG can be used for assessing glucose metabolism in the brain and for imaging cancer tumors. After injection into the blood, FDG is taken up by "FDG-avid" tissues with a high need for glucose, such as the brain and most types of malignant tumors. Tomography, often assisted by a computer to form a PET/CT (CT stands for "computer tomography") machine, can then be used to diagnose or monitor treatment of cancers, especially Hodgkin's lymphoma, lung cancer, and breast cancer.

Natural fluorine is monoisotopic, consisting solely of fluorine-19. Fluorine compounds are highly amenable to nuclear magnetic resonance (NMR), because fluorine-19 has a nuclear spin of ​¹⁄₂, a high nuclear magnetic moment, and a high magnetogyric ratio. Fluorine compounds typically have a fast NMR relaxation, which enables the use of fast averaging to obtain a signal-to-noise ratio similar to hydrogen-1 NMR spectra. Fluorine-19 is commonly used in NMR study of metabolism, protein structures and conformational changes. In addition, inert fluorinated gases have the potential to be a cheap and efficient tool for imaging lung ventilation.

Oxygen transport research

Liquid fluorocarbons have a very high capacity for holding gas in solution. They can hold more oxygen or carbon dioxide than blood does. For that reason, they have attracted ongoing interest related to the possibility of artificial blood or of liquid breathing.

Computer-generated model of nanocrystal of perflubron (red) and gentamicin (white, an antibiotic)

 

Blood substitutes are the subject of research because the demand for blood transfusions grows faster than donations. In some scenarios, artificial blood may be more convenient or safe. Because fluorocarbons do not normally mix with water, they must be mixed into emulsions (small droplets of perfluorocarbon suspended in water) in order to be used as blood. One such product, Oxycyte, has been through initial clinical trials.

Possible medical uses of liquid breathing (which uses pure perfluorocarbon liquid, not a water emulsion) involve assistance for premature babies or for burn victims (if normal lung function is compromised). Both partial and complete filling of the lungs have been considered, although only the former has undergone any significant tests in humans. Several animal tests have been performed and there have been some human partial liquid ventilation trials. One effort, by Alliance Pharmaceuticals, reached clinical trials but was abandoned because of insufficient advantage compared to other therapies.

Nanocrystals represent a possible method of delivering water- or fat-soluble drugs within a perfluorochemical fluid. The use of these particles is being developed to help treat babies with damaged lungs.

Perfluorocarbons are banned from sports, where they may be used to increase oxygen use for endurance athletes. One cyclist, Mauro Gianetti was investigated after a near fatality where PFC use was suspected.

Other posited applications include deep sea diving and space travel, applications that both require total, not partial, liquid ventilation. The 1989 film The Abyss showed a fictional use of perfluorocarbon for human diving but also filmed a real rat surviving while cooled and immersed in perfluorocarbon.

Agrichemicals

An estimated 30% of agrichemical compounds contain fluorine. Most of them are used as poisons, but a few stimulate growth instead. 

Sign warning of poisonous sodium fluoroacetate baits

 

Sodium fluoroacetate has been used as an insecticide, but it is especially effective against mammalian pests. The name "1080" refers to the catalogue number of the poison, which became its brand name. Fluoroacetate is similar to acetate, which has a pivotal role in the Krebs cycle (a key part of cell metabolism). Fluoroacetate halts the cycle and causes cells to be deprived of energy. Several other insecticides contain sodium fluoride, which is much less toxic than fluoroacetate. Insects fed 29-fluorostigmasterol use it to produce fluoroacetates. If a fluorine is transferred to a body cell, it blocks metabolism at the position occupied.

Trifluralin was widely used in the 20th century, for example, in over half of U.S. cotton field acreage in 1998.) Because of its suspected carcinogenic properties some Northern European countries banned it in 1993. As of 2015, the European Union has banned it, although Dow made a case to cancel the decision in 2011.

Biochemistry

South Africa's gifblaar is one of the few organisms that naturally produce fluorine compounds.

 

Biologically synthesized organofluorines are few in number, although some are widely produced. The most common example is fluoroacetate, with an active poison molecule identical to commercial "1080". It is used as a defense against herbivores by at least 40 green plants in Australia, Brazil, and Africa; other biologically synthesized organofluorines include ω-fluoro fatty acids, fluoroacetone, and 2-fluorocitrate. In bacteria, the enzyme adenosyl-fluoride synthase, which makes the carbon–fluorine bond, has been isolated. The discovery was touted as possibly leading to biological routes for organofluorine synthesis.

Fluoride is considered a semi-essential element for humans: not necessary to sustain life, but contributing (within narrow limits of daily intake) to dental health and bone strength. Daily requirements for fluorine in humans vary with age and sex, ranging from 0.01 mg in infants below 6 months to 4 mg in adult males, with an upper tolerable limit of 0.7 mg in infants to 10 mg in adult males and females. Small amounts of fluoride may be beneficial for bone strength, but this is an issue only in the formulation of artificial diets.

Hazards

NFPA 704 fire diamond
0 4 4 W           The fire diamond hazard sign for elemental fluorine.

The U.S. hazard signs for commercially transported fluorine

Fluorine gas

Elemental fluorine is highly toxic. Above a concentration of 25 ppm, it causes significant irritation while attacking the eyes, airways and lungs and affecting the liver and kidneys. At a concentration of 100 ppm, human eyes and noses are seriously damaged. People can be exposed to fluorine in the workplace by breathing it in, skin contact, or eye contact. The Occupational Safety and Health Administration (OSHA) has set the legal limit (Permissible exposure limit) for fluorine exposure in the workplace as 0.1 ppm (0.2 mg/m³) over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 0.1 ppm (0.2 mg/m³) over an 8-hour workday. At levels of 25 ppm, fluorine is immediately dangerous to life and health.

Hydrofluoric acid

Typical HF burns: the outward signs may not be evident for 24 hours, after which calcium treatments are less effective.

 

Hydrofluoric acid, the water solution of hydrogen fluoride, is a contact poison. Even though it is chemically only a weak acid, it is far more dangerous than conventional strong mineral acids, such as nitric acid, sulfuric acid, or hydrochloric acid. Owing to its lesser chemical dissociation in water (remaining a neutral molecule), hydrogen fluoride penetrates tissue more quickly than typical acids. Poisoning can occur readily through the skin or eyes or when inhaled or swallowed. From 1984 to 1994, at least nine U.S. workers died from accidents with HF.

Once in the blood, hydrogen fluoride reacts with calcium and magnesium, resulting in electrolyte imbalance (potentially hypocalcemia). The consequent effect on the heart (cardiac arrhythmia) may be fatal. Formation of insoluble calcium fluoride also causes strong pain. Burns with areas larger than 160 cm², about the size of a man's hand, can cause serious systemic toxicity.

Symptoms of exposure to hydrofluoric acid may not be immediately evident, with an 8-hour delay for 50% HF and up to 24 hours for lower concentrations. Hydrogen fluoride interferes with nerve function, meaning that burns may not initially be painful. 

If the burn has been initially noticed, then HF should be washed off with a forceful stream of water for ten to fifteen minutes to prevent its further penetration into the body. Clothing used by the person burned may also present a danger. Hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca²⁺ that binds with the fluoride ions. Skin burns can be treated with a water wash and 2.5 percent calcium gluconate gel or special rinsing solutions. Because HF is absorbed, further medical treatment is necessary. Calcium gluconate may be injected or administered intravenously. Use of calcium chloride is contraindicated and may lead to severe complications. Sometimes surgical excision of tissue or amputation is required.

Fluoride ion

Moroccan cow with fluorosis, from industrial contamination

Soluble fluorides are moderately toxic. For sodium fluoride, the lethal dose for adults is 5–10 g, which is equivalent to 32–64 mg of elemental fluoride per kilogram of body weight. The dose that may lead to adverse health effects is about one fifth of the lethal dose. Chronic excess fluoride consumption can lead to skeletal fluorosis, a disease of the bones that affects millions in Asia and Africa.

The fluoride ion is readily absorbed by the stomach and intestines. Ingested fluoride forms hydrofluoric acid in the stomach. In this form, fluoride crosses cell membranes and then binds with calcium and interferes with various enzymes. Fluoride is excreted through urine. Fluoride exposure limits are based on urine testing, which is used to determine the human body's capacity for ridding itself of fluoride.

Historically, most cases of fluoride poisoning have been caused by accidental ingestion of insecticides containing inorganic fluoride. Most calls to poison control centers for possible fluoride poisoning come from the ingestion of fluoride-containing toothpaste. Malfunction of water fluoridation equipment has occurred several times, including an Alaskan incident that sickened nearly 300 people and killed one.

Biopersistence

Because of the strength of the carbon–fluorine bond, organofluorines endure in the environment. Perfluorinated compounds (PFCs) have attracted particular attention as persistent global contaminants. These compounds can enter the environment from their direct uses in waterproofing treatments and firefighting foams or indirectly from leaks from fluoropolymer production plants (where they are intermediates). Because of the acid group, PFCs are water-soluble in low concentrations. While there are other PFAAs, the lion's share of environmental research has been done on the two most well-known: perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). The U.S. Environmental Protection Agency classifies these materials as "emerging contaminants" based on the growing but still incomplete understanding of their environmental impact.

Trace quantities of PFCs have been detected worldwide, in organisms from polar bears in the Arctic to the global human population. Both PFOS and PFOA have been detected in breast milk and the blood of newborns. A 2013 review showed widely varying amounts of PFOS and PFOA in different soils and groundwater, with no clear pattern of one chemical dominating. PFC concentrations were generally higher in areas with more human population or industrial activity, and areas with more PFOS generally also had more PFOA. the two chemicals have been found at different concentrations in different populations; for example, one study showed more PFOS than PFOA in Germans, while another study showed the reverse for Americans. PFCs may be starting to decrease in the biosphere: one study indicated that PFOS levels in wildlife in Minnesota were decreasing, presumably because 3M discontinued its production.

The PFOS molecule

In the body, PFCs bind to proteins such as serum albumin. Their tissue distribution in humans is unknown, but studies in rats suggest it is present mostly in the liver, kidney, and blood. They are not metabolized by the body but are excreted by the kidneys. Dwell time in the body varies greatly by species. Rodents have half-lives of days, while in humans they remain for years. Many animals show sex differences in the ability to rid the body of PFAAs, but without a clear pattern. Gender differences of half lives vary by animal species.

The potential health impact of PFCs is unclear. Unlike chlorinated hydrocarbons, PFCs are not lipophilic (stored in fat), nor genotoxic (damaging genes). Both PFOA and PFOS in high doses cause cancer and the death of newborns in rodents. Studies on humans have not been able to prove an impact at current exposures. Bottlenose dolphins have some of the highest PFOS concentrations of any wildlife studied; one study suggests an impact on their immune systems.

The biochemical causes of toxicity are also unclear and may differ by molecule, health effect, and even animal. PPAR-alpha is a protein that interacts with PFAAs and is commonly implicated in contaminant-caused rodent cancers.

Less fluorinated chemicals (i.e. not perfluorinated compounds) can also be detected in the environment. Because biological systems do not metabolize fluorinated molecules easily, fluorinated pharmaceuticals like antibiotics and antidepressants can be found in treated city sewage and wastewater. Fluorine-containing agrichemicals are measurable in farmland runoff and nearby rivers.