According to the method, range or scope of its study, or the focus of interest of the linguist, Linguistics can be classified into different kinds, the chief of which are noted below: Diachronic Linguistics and Synchronic Linguistics. Diachronic linguistics is the kind in which we study the historical development of language through different periods of time.For example, we study how French and Italian have grown out of Latin. The changes that have occurred in language with the passage of time, are also studied under this kind of linguistics; therefore, it is called historical linguistics. Synchronic linguistics is not concerned with the historical development of language. It confines itself to the study of how a language is spoken by a specified speech community at a particular point of time. It is also called 'descriptive' linguistics. Diachronic linguistics studies language change, and synchronic linguistics studies language states without their history. According to C.F. Hockett:
"The study of how a language works at a given time, regardless of its past history or future destiny, is called descriptive or synchronic linguistics. The study of how speech habits change as time goes by is called historical or diachronic linguistics”
The distinction synchrony and diachrony refers to the difference in treating language from different points of view. Though the historical character of a language cannot be ignored, its present form being the result of definite historical processes, changes and transformations, it is necessary for a complete understanding of it to concentrate on the units of its structure at the present moment. Some scholars do not see the two approaches apart. They assert that it is a mistake to think of descriptive and historical linguistics as two separate compartments. However, on the whole the two areas are kept apart and one is studied to the exclusion of the other. Synchronic statements make no reference to the previous stages in the language. Linguistic studies in the nineteenth century were historical in character; they originated as part of the general historical investigations into the origins and development of cultures and communities, especially
West Asia, , etc. Such philological researches viewed language at different stages of its progress and attempted to understand relations among different languages. Language families were discovered and genetic affinities identified. For Zhirmunsky, Diachronic linguistics was a great discovery of the 19th century: Egypt
“Which developed so powerfully and fruitfully from the 1820s to the 1880s. This discovery enabled linguists to explain modern languages as a result of law-governed historical development”
On a closer look one realizes that without a good synchronic (descriptive) work, valid historical (diachronic) postulations are not possible; in other words, a good historical linguist needs to be thorough descriptive scholar too.
The figure above shows the distinction. Diachronic axis (x-y) has been considered moving and the synchronic axis static. It was Swiss linguist Ferdinand de Sassure who first coined these terms and established the distinctions. As the Russian linguist V.M. Zhirmunsky observes, ‘In de Saussure’s conception, synchrony is language considered as a system of static oppositions resting on a single temporal plane, a static two dimensional cross-section”. The principles that introduce this dichotomy enable us to obtain, according to Wilkins, ‘particularly accurate information about a language in its current usage’. For Saussure, Historical considerations are irrelevant to the investigation of particular temporal states of a language. But Saussure’s analogy of chess breaks at the point that players determine the course of any particular game that is being played in opposition to one another and with reference to a recognized goal. As far as we know, there is no directionality in the diachronic development of languages.