Man's study of language can be traced back to ancient Greek (about 500 BC) in the western world. In different historical periods, the object of study and method of study vary. Modern linguistics began in the early 20th century. Its founder is the Swiss scholar, Ferdinand de Saussure. His lectures (reconstructed from the notes of his students) were published posthumously in 1915 as Course in General Linguistics (first in French and later translated into English). The book changed the orientation of linguistics. Linguistics has since been distinguished from the linguistics of the previous periods in some respects. Firstly, priority is given, as mentioned earlier, to spoken language. Secondly, focus is on synchronic study of language, rather than on diachronic study of language. Linguists are more interested in the study of contemporary language than in the study of the evolution of languages (In this respect, it differs from historical linguistics or philology).Thirdly, modern linguistics is descriptive rather than prescriptive in nature. Linguists endeavor to state objectively the regularities of a language. They aim at finding out how a language is spoken, they do not attempt to tell people how it should be spoken (In this regard, it is different from traditional grammar). Fourthly, modern linguistics is theoretically rather than pedagogically oriented. Modern linguists strive to construct theories of language that can account for language in general. The aim is not at writing a grammar of a language that can be directly used as a reference book in language teaching and learning. This feature distinguishes modern linguistics from traditional grammar. The two are complementary, not contradictory. Knowledge of both is necessary for a language teacher; knowledge of the latter is necessary for a language learner.