Know thyself

"Know thyself" (Greek: Γνῶθι σεαυτόν, gnōthi seauton) is a philosophical Delphic-maxim which was inscribed upon the Temple of Apollo in the ancient Greek precinct of Delphi. The best-known of the Delphic maxims, it has been quoted and analyzed by numerous authors throughout history, and has been applied in many ways. Although traditionally attributed to the Seven Sages of Greece, or to the god Apollo himself, the inscription likely had its origin in a popular proverb.

Ion of Chios makes the earliest explicit allusion to the maxim in a fragment dating to the 5th century BC, though the philosopher Heraclitus, active towards the end of the previous century, may also have made reference to the maxim in his works. The principal meaning of the phrase in its original application was "know your limits" – either in the sense of knowing the extent of one's abilities, knowing one's place in the world, or knowing oneself to be mortal. In the 4th century BC, however, the maxim was drastically re-interpreted by Plato, who understood it to mean, broadly speaking, "know your soul".

In later writings on the subject, one common theme was that one could acquire knowledge of the self by studying the universe, or knowledge of the universe by studying the self. This was often explained in terms of the microcosm–macrocosm analogy, the idea that a human being is structurally similar to the cosmos. Another theme, which can be traced back to the Platonic Alcibiades I, is that one can only know oneself by observing other people.

Christian, Jewish and Islamic authors found various scriptural equivalents for the maxim, allowing them to discuss the topic of self-knowledge without reference to the pagan inscription. By the time of the Protestant Reformation, Christian theologians generally understood the maxim to enjoin, firstly, knowledge of the soul's origin in God, and secondly, knowledge of the sinfulness of human nature. In secular writings of the period, several new meanings emerged; among them, that "know thyself" was a command to study the physical properties of the human body.

During the 19th and 20th centuries, the maxim acquired several new associations. It was frequently quoted in German philosophy and literature, by authors such as Kant, Hegel and Goethe; it was cited as an analogue of "tat tvam asi" ("that thou art"), one of the "Great Sayings" of Hinduism; and it took on an important role in the developing discipline of psychoanalysis, where it was interpreted as an injunction to understand the unconscious mind.

According to ancient Greek and Roman authors, there were three maxims prominently inscribed upon the Temple of Apollo at Delphi: "know thyself", "nothing too much" and "give a pledge and trouble is at hand". Their exact location is uncertain; they are variously stated to have been on the wall of the pronaos (forecourt), on a column, on a doorpost, on the temple front, or on the propylaea (gateway). The date of their inscription is also unknown, but they were present at least as early as the 5th century BC. Although the temple was destroyed and rebuilt several times over the years, the maxims appear to have persisted into the Roman era (1st century AD), at which time, according to Pliny the Elder, they were written in letters of gold.

The three sayings were traditionally said to have originated with the Seven Sages, a legendary group of philosophers and statesmen who flourished in the 6th century BC. The first known reference to the Seven Sages is in Plato's Protagoras, where they are said to have collectively authored the first two maxims. The names of the sages are given by Plato as Thales, Pittacus, Bias, Solon, Cleobulus, Myson and Chilon; but in the works of later writers, some of these names are dropped and others added in their place. Each of the maxims was often attributed to a particular sage, and some authors, such as Demetrius of Phalerum, assigned additional sayings to the four remaining sages. There was no general agreement over which maxim belonged to which sage, but "know thyself" was most commonly attributed to Chilon.

Another popular theory held that the maxims were first spoken by the Delphic oracle, and therefore represented the wisdom of the god Apollo. Clearchus of Soli, among others, attempted to reconcile the two accounts by claiming that Chilon, enquiring of the oracle what was best to be learnt, received the answer "know thyself", and subsequently adopted the maxim as his own. In all likelihood, however, the sayings were simply common proverbs of much earlier date, which gained a new significance from their prominent position on the temple.