In this article I intend to say that the linguistic theory of transformational grammar may be taken as an informal axiomatic system, since kernal or basic sentence structures play the role of axioms; final derived sentence structures, theorems; and transformational rules, rules of inference. From this point of view it is important to distinguish "basic" structures from "derived" structures. In his "Aspects of the Theory of Syntax," N. Chomsky says that a deep structure expresses the content of a sentence, and that a surface structure indicates its form. Now, what is the "content" of a sentence? According to Chomsky, since the sentences such as "John can go," and "Can John go?" have the same content, their deep structures reduce to one. If so, we have to conclude that the sentences "John cannot go," "John may go," "John shall go," "John goes," "John went," and "John did not go," have the same content and their deep structures reduce the one structure which may be expressed as G(J), G being a functional constant and J being an individual constant. Thus since a deep structure of a sentence coincides with its logic, it is possible to construct, in the strict sense, the system of transformational grammar on the logical basis.