In Linguistic, two different and complementary points of view can be adopted when facts of language are analyzed: diachrony

• the approach known as diachronic is interested in the history of the language and studies its evolutions (etymology, phonetic evolutions, Sémantique S, lexical, syntactic, etc). The term is a erudite loan built on Greek Racines, δια-, “through”, and χρόνος, “time”; the compared Linguistic , for example, has a diachronic approach;

• the approach known as synchronic is interested in a language at one exact moment of its history ; the word is also manufactured starting from two terms of the Greek : συν-, “with”, χρόνος, “time”. The school Grammaire is essentially synchronic: it indicates which are the Norme S considered as rules of a language, which can have changed former states since.

Opposition between synchrony and diachrony thus what these two terms in this meaning are due to Ferdinand de Saussure, first linguist to have separated the two visual angles clearly.

This opposition is profitable also in philosophy, where it was exploited inter alia by Barthes and Sartre.

In psychology of the development, this opposition " synchronie" - " diachronie" return respectively to an analysis of approach microdéveloppementale (modern) or macrodéveloppementale (theories piagétiennes).