applied in a particular order to the kernel sentences. At the final stage of the grammar, morphophonemic rules convert a string of words into a string of phonemes. Chomsky then applies this idea of transformational rules in the English auxiliary verb system. Borrowing of terminology In Syntactic Structures, the term "transformation" was borrowed from the works of Zellig Harris. Harris was Chomsky's initial mentor. Harris used the term "transformation" to describe equivalence relations between sentences of a language. By contrast, Chomsky's used the term to describe a formal rule applied to underlying structures of sentences. Chomsky also borrowed the term "generative" from a previous work of mathematician Emil Post. Post wanted to "mechanically [derive] inferences from an initial axiomatic sentence". Chomsky applied Post's work on logical inference to describe sets of strings (sequence of letters or sounds) of a human language. When he says a finite set of rules "generate" (i.e. "recursively enumerate") the set of potentially infinite number of sentences of a particular human language, he means that they provide an explicit, structural description of those sentences. Justification of grammars In the sixth chapter titled "On the Goals of Linguistic Theory", Chomsky writes that his "fundamental concern" is "the problem of justification of grammars". He draws parallels between the theory of language and theories in physical sciences. He compares a finite corpus of utterances of a particular language to "observations". He likens grammatical rules to "laws" which are stated in terms of "hypothetical constructs" such as phonemes, phrases, etc. According to Chomsky, the criteria for the "justification of grammars" are "external conditions of adequacy", the "condition of generality" and "simplicity". To choose the best possible grammar for a given corpus of a given language, Chomsky shows his preference for the "evaluation procedure" (which uses the aforementioned criteria). He rejects the "discovery procedure" (employed in structural linguistics and supposed to automatically and mechanically produce the correct grammar of a language from a corpus). He also dismisses the "decision procedure" (supposed to automatically choose the best grammar for a language from a set of competing grammars). Chomsky thus shows preference for "explanatory depth" with some "empirical inadequacies" over the pursuit of very detailed empirical coverage of all data. Application of transformational grammar in English In the seventh chapter titled "Some Transformations in English", Chomsky strictly applies his just-proposed transformation-based approach on some aspects of English. He treats at length the formation