It is a fact that languages change through the time. The language of the Anglo-Saxons was different from the language of Chaucer, this differed from the language of Shakespeare, and present-day English is different, in its turn, from all previous stages of its development.
Synchronic linguistics: is the study of language at one point of time. It has also been called "Descriptive Linguistics". A language is frozen, as it were, photographed, and described independently of its previous or later states.
Diachronic Linguistics (or Historical Linguistics ) is the study of linguistic change through time. This is basically a comparative study.
Logically, synchronic studies are prior to diachronic studies because in order to compare two things we should describe them separately.
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