Panini formulates close to 4,000 rules which together form a compact generative grammar of Sanskrit. Inherent in his analytic approach are the concepts of the phoneme, the morpheme and the root. Due to its focus on brevity, his grammar has a highly unintuitive structure, reminiscent of contemporary "machine language" (as opposed to "human readable" programming languages).Indian linguistics maintained a high level for several centuries; Patanjali in the 2nd century BC still actively criticizes Panini. In the later centuries BC, however, Panini's grammar came to be seen as prescriptive, and commentators came to be fully dependent on it. Bhartrhari (c. 450 510) theorized the act of speech as being made up of four stages: first, conceptualization of an idea, second, its verbalization and sequencing (articulation) and third, delivery of speech into atmospheric air, the interpretation of speech by the listener, the interpreter.Western linguistics begins in Classical Antiquity with grammatical speculation such as Plato's Cratylus. The first important advancement of the Greeks was the creation of the alphabet. As a result of the introduction of writing, poetry such as the Homeric poems became written and several editions were created and commented, forming the basis of philology and critic. The sophists and Socrates introduced dialectics as a new text genre. Aristotle defined the logic of speech and the argument, and his works on rhetoric and poetics developed the understating of tragedy, poetry, and public discussions as text genres.One of the greatest of the Greek grammarians was Apollonius Dyscolus.[18] Apollonius wrote more than thirty treatises on questions of syntax, semantics, morphology, prosody,orthography, dialectology, and more. In the 4th c., Aelius Donatus compiled the Latin grammar Ars Grammatica that was to be the defining school text through the Middle Ages.[19] In De vulgari eloquentia ("On the Eloquence of Vernacular"), Dante Alighieri expanded the scope of linguistic enquiry from the traditional languages of antiquity to include the language of the day.[citation needed]In the Middle East, the Persian linguist Sibawayh made a detailed and professional description of Arabic in 760, in his monumental work, Al-kitab fi al-nahw ( , The Book on Grammar), bringing many linguistic aspects of language to light. In his book he distinguished phonetics from phonology.[citation needed]Sir William Jones noted that Sanskrit shared many common features with classical Latin and Greek, notably verb roots and grammatical structures, such as the case system. This led to the theory that all languages sprung from a common source and to the discovery of the Indo-European language family. He began the study of comparative linguistics, which would uncover more language families and branches.In 19th century Europe the study of linguistics was largely from the perspective of philology (or historical linguistics). Some early-19th-century linguists were Jakob Grimm, who devised a principle of consonantal shifts in pronunciation known as Grimm's Law in 1822; Karl Verner, who formulated Verner's Law; August Schleicher, who created the "Stammbaumtheorie" ("family tree"); and Johannes Schmidt, who developed the "Wellentheorie" ("wave model") in 1872.Ferdinand de Saussure was the founder of modern structural linguistics, with an emphasis on synchronic (i.e. nonhistorical) explanations for language form.In North America, the structuralist