Aspects of the Theory of Syntax (known in linguistic circles simply as Aspects) is a book on linguistics written by American linguist Noam Chomsky, first published in 1965. In Aspects, Chomsky presented a deeper, more extensive reformulation of transformational generative grammar (TGG), a new kind of syntactic theory that he had introduced in the 1950s with the publication of his first book, Syntactic Structures. Aspects is widely considered to be the foundational document and a proper book-length articulation of Chomskyan theoretical framework of linguistics. It presented Chomsky's epistemological assumptions with a view to establishing linguistic theory-making as a formal (i.e. based on the manipulation of symbols and rules) discipline comparable to physical sciences, i.e. a domain of inquiry well-defined in its nature and scope. From a philosophical perspective, it directed mainstream linguistic research away from behaviorism, constructivism, empiricism and structuralism and towards mentalism, nativism, rationalism and generativism, respectively, taking as its main object of study the abstract, inner workings of the human mind related to language acquisition and production.