The causes of continuity are a priori within the scope of the observer, but the causes of change in time are not. It is better not to attempt giving … - Ferdinand de Saussure

La langue est un systéme dont toutes les parties peuvent et doivent être considérés dans leur solidarité synchronique.

Thus we may found the science for the study of the life of signs against the background of social life; it would form part of social psychology, and consequently of general psychology; we shall call it semiology (from Greek sēmeion — 'sign'). That science would explain to us in what signs consist of and by what laws they are governed. Since it is a science which does not yet exist, we do not know what it will be like; it has, however, a reason for its existence, its place is allocated in advance. Linguistics is only a part of that general science ; the laws which semiology will discover, will be applicable also to linguistics, which in turn will be linked with a domain clearly defined throughout the entirety of human affairs.

Language is a system of signs that express ideas, and is therefore comparable to a system of writing, the alphabet of deaf-mutes, symbolic rites, polite formulas, military signals, etc. But it is the most important of all these systems.