Eclecticism in architecture at the intersection of Rákóczi Avenue and the Grand Boulevard in Budapest
Detail of an Eclectic house in Bucharest (Romania), a combination between Neoclassical architecture and Romanian Revival
Eclecticism is a conceptual approach that does not hold rigidly to a single paradigm
 or set of assumptions, but instead draws upon multiple theories, 
styles, or ideas to gain complementary insights into a subject, or 
applies different theories in particular cases. However, this is often 
without conventions or rules dictating how or which theories were 
combined.
It can sometimes seem inelegant or lacking in simplicity, and 
eclectics are sometimes criticized for lack of consistency in their 
thinking. It is, however, common in many fields of study. For example, 
most psychologists accept certain aspects of behaviorism, but do not attempt to use the theory to explain all aspects of human behavior.
Origin
Eclecticism was first recorded to have been practiced by a group of ancient Greek and Roman philosophers
 who attached themselves to no real system, but selected from existing 
philosophical beliefs those doctrines that seemed most reasonable to 
them. Out of this collected material they constructed their new system 
of philosophy. The term comes from the Greek ἐκλεκτικός (eklektikos), literally "choosing the best", and that from ἐκλεκτός (eklektos), "picked out, select". Well known eclectics in Greek philosophy were the Stoics Panaetius and Posidonius, and the New Academics Carneades and Philo of Larissa. Among the Romans, Cicero was thoroughly eclectic, as he united the Peripatetic, Stoic, and New Academic doctrines. Philo's successor and Cicero's teacher Antiochus of Ascalon is credited with influencing the Academy so that it finally transitioned from Scepticism to Eclecticism. Other eclectics included Varro and Seneca the Younger. 
According to Rošker and Suhadolnik, however, even though 
eclecticism had a Greek origin, the term was rarely used and it was even
 given a negative connotation by historians of Greek thought, 
associating it with the description for impure and unoriginal thinking. Scholars such as Clement of Alexandria
 maintained that eclecticism had a long history in Greek philosophy and 
it is underpinned by a deeper metaphysical and theological conviction 
concerning the absolute/God as the source of all noble thoughts and that
 all parts of the truth can be found among the various philosophical 
systems.
Architecture and art
The term eclecticism is used to describe the combination, in a single
 work, of elements from different historical styles, chiefly in 
architecture and, by implication, in the fine and decorative arts. The 
term is sometimes also loosely applied to the general stylistic variety 
of 19th-century architecture after neoclassicism (c. 1820), although the revivals of styles in that period have, since the 1970s, generally been referred to as aspects of historicism.
Eclecticism plays an important role in critical discussions and 
evaluations but is somehow distant from the actual forms of the 
artifacts to which it is applied, and its meaning is thus rather 
indistinct. The simplest definition of the term—that every work of art 
represents the combination of a variety of influences—is so basic as to 
be of little use. In some ways Eclecticism is reminiscent of Mannerism
 in that the term was used pejoratively for much of the period of its 
currency, although, unlike Mannerism, Eclecticism never amounted to a 
movement or constituted a specific style: it is characterized precisely 
by the fact that it was not a particular style. 
Martial arts
Some martial arts can be described as eclectic in the sense that they borrow techniques from a wide variety of other martial arts. 
Philology
In textual criticism,
 eclecticism is the practice of examining a wide number of text 
witnesses and selecting the variant that seems best. The result of the 
process is a text with readings drawn from many witnesses. In a purely 
eclectic approach, no single witness is theoretically favored. Instead, 
the critic forms opinions about individual witnesses, relying on both 
external and internal evidence.
Since the mid-19th century, eclecticism, in which there is no a priori bias to a single manuscript, has been the dominant method of editing the Greek text of the New Testament (currently, the United Bible Society, 4th ed. and Nestle-Åland, 27th ed.). Even so, the oldest manuscripts, being of the Alexandrian text-type, are the most favored, and the critical text has an Alexandrian disposition.
Philosophy
In ancient philosophy, the Eclectics
 use elements from multiple philosophies, texts, life experiences and 
their own philosophical ideas. These ideas include life as connected 
with existence, knowledge, values, reason, mind, and language. Antiochus of Ascalon (c. 125 – c. 69 BC) was the pupil of Philo of Larissa, and the teacher of Cicero. Through his influence, Platonism made the transition from New Academy skepticism to Eclecticism.
 Whereas Philo had still adhered to the doctrine that there is nothing 
absolutely certain, Antiochus returned to a pronounced dogmatism. Among 
his other objections to skepticism was the consideration that without 
firm convictions no rational content of life is possible.
 Antiochus pointed out that it is a contradiction to assert that nothing
 can be asserted or to prove that nothing can be proved; that we cannot 
speak of false ideas and at the same time deny the distinction between 
false and true. He expounded the Academic, Peripatetic, and Stoic systems in such a way as to show that these three schools deviate from one another only in minor points. Antiochus himself was chiefly interested in ethics, in which he tried to find a middle way between Zeno, Aristotle, and Plato. For instance, he said that virtue suffices for happiness, but for the highest grade of happiness, bodily and external goods are necessary as well.
This eclectic tendency was favoured by the lack of dogmatic works by Plato.
 Middle Platonism was promoted by the necessity of considering the main 
theories of the post-Platonic schools of philosophy, such as the 
Aristotelian logic and the Stoic psychology and ethics (theory of goods 
and emotions).
 On the one hand the Middle Platonists were engaged like the later 
Peripatetics in scholarly activities such as the exposition of Plato's 
doctrines and the explanation of his dialogues; on the other hand they 
attempted to develop the Platonic theories systematically. In so far as 
it was subject in this to the influence of Neopythagoreanism, it was of considerable importance in preparing the way for Neoplatonism.
Psychology
Eclecticism is recognized in approaches to psychology that see many factors influencing behavior and cognition or psyche. In the 1970s, psychologists started using whichever approaches and techniques that they deemed appropriate for their client. They take multiple perspectives into consideration while identifying, explaining, and changing the behavior of the client.