How we change what others think, feel, believe and do
Synchrony and Diachrony
Saussure proposed that language as a system of signs be studied as a complete system at any given point in time.
Like chess, the important part of language is how pieces move and the positions of all pieces relative to one another. The shape of each piece is only important in that its potential can be recognized.
A synchronic relationship is one where two similar things exist at the same time. Modern American English and British English have a synchronic relationship.
Diachrony is the change in the meaning of words over time.
For example in the way that 'magic' meant 'good' in youth culture for a period during the 1980s (and, to a lesser extent, beyond).
It is thus the study of language in terms of how it visibly changes in usage. It is based in the dictionary meaning of words.
A diachronic relationship is where related things exist separated by time. 12th century English and 21st century English have a diachronic relationship.
Saussure criticized current linguistics as seeking to understand language changes but not why it changed or what underlying factors were really changing.
He thus moved the study of language from diachronic to synchronic relationships.