A grammar of a language purports to be a description of the ideal speaker-hearer’s intrinsic competence. If the grammar is, furthermore, perfectly explicit—in other words, if it does not rely on the intelligence of the understanding reader but rather provides an explicit analysis of his contribution—we may (somewhat redundantly) call it a generative grammar.

In general, there is no doubt that a theory of language, regarded as a hypothesis about the innate “language-forming capacity” of humans, should concern itself with both substantive and formal universals. But whereas substantive universals have been the traditional concern of general linguistic theory, investigations of the abstract conditions that must be satisfied by any generative grammar have been undertaken only quite recently. They seem to offer extremely rich and varied possibilities for study in all aspects of grammar.

For language to be generative, children must not be learning by rote. Music is also generative. For every musical phrase I hear, I can always add a note... to generate a new musical phrase.

The child must acquire a generative grammar of his language on the basis of a fairly restricted amount of evidence. To account for this achievement, we must postulate a sufficiently rich internal structure – a sufficiently restricted theory of universal grammar that constitutes his contribution to language acquisition.

In practice, the linguist is always involved in the study of both universal and particular grammar. When he constructs a descriptive, particular grammar in one way rather than another on the basis of what evidence he has available, he is guided, consciously or not, by certain assumptions as to the form of grammar, and these assumptions belong to the theory of universal grammar. Conversely, his formulation of principles of universal grammar must be justified by the study of their consequences when applied in particular grammars. Thus, at several levels the linguist is involved in the construction of explanatory theories, and at each level there is a clear psychological interpretation for his theoretical and descriptive work.

In studying the evolution of mind, we cannot guess to what extent there are physically possible alternatives to, say, transformational generative grammar, for an organism meeting certain other physical conditions characteristic of humans. Conceivably, there are none – or very few – in which case talk about evolution of the language capacity is beside the point. The vacuity of such speculation, however, has no bearing one way or another on those aspects of the problem of mind that can be sensibly pursued. It seems to me that these aspects are, for the moment, the problems illustrated in the case of language by the study of the nature, the use, and the acquisition of linguistic competence.

Returning to the main theme, we can apparently define a grammatical transformation in terms of a “structure index” that is a Boolean condition on Analyzability and a sequence of elementary transformations drawn from a base set including substitutions, deletions, and adjunctions. It seems also that these form larger repeated units (for example, substitution-deletions, erasures) and that the limitations on their application can be given by general conventions of the sort just mentioned. If this is correct, then the formal properties of the theory of transformations become fairly clear and reasonably simple, and it may be possible to undertake abstract study of them of a sort that has not been feasible in the past.

A linguistic theory must contain a definition of “grammar,” that is, a specification of the class of potential grammars. We may, correspondingly, say that a linguistic theory is descriptively adequate if it makes a descriptively adequate grammar available for each natural language.

There is always the danger that the use of traditional grammatical terms with reference to a wide variety of languages may be taken to imply a secret belief in universal grammar. Every analysis of a particular ‘language’ must of necessity determine the values of the ad hoc categories to which traditional names are given. What is here being sketched is a general linguistic theory applicable to particular linguistic descriptions, not a theory of universals for general linguistic description.

The grammar of a language is a complex system with many and varied interconnections between its parts. In order to develop one part of grammar thoroughly, it is often useful, or even necessary, to have some picture of the character of a completed system. Once again, I think that the notion that syntactic theory must await the solution of problems of phonology and morphology is completely untenable whether or not one is concerned with the problem of discovery procedures, but I think it has been nurtured by a faulty analogy between the order of development of linguistic theory and the presumed order of operations in discovery of grammatical structure.

The search for rigorous formulation in linguistics has a much more serious motivation than mere concern for logical niceties or the desire to purify well-established methods of linguistic analysis. Precisely constructed models for linguistic structure can play an important role, both negative and positive, in the process of discovery itself. By pushing a precise but inadequate formulation to an unacceptable conclusion, we can often expose the exact source of this inadequacy and, consequently, gain a deeper understanding of the linguistic data. More positively, a formalized theory may automatically provide solutions for many problems other than those for which it was explicitly designed. Obscure and intuition-bound notions can neither lead to absurd conclusions nor provide new and correct ones, and hence they fail to be useful in two important respects. I think that some of those linguists who have questioned the value of precise and technical development of linguistic theory may have failed to recognize the productive potential in the method of rigorously stating a proposed theory and applying it strictly to linguistic material with no attempt to avoid unacceptable conclusions by ad hoc adjustments or loose formulation.

There is another kind of studies which distinguished from the sometimes opposed to comparative grammar. It is known under the name of general or philosophical grammar , whose principles and observations were articulated by Port Royal and which deals with the relation of the form of language to the operations of the mind.

In any event, the questions we have touched on here have not yet been illuminated in any serious way by approaching them within the framework of any explicit grammatical theory. For the present, one can barely go beyond mere taxonomic arrangement of data. Whether these limitations are intrinsic, or whether a deeper analysis can succeed in unraveling some of these difficulties, remains an open question.

In brief, it is clear that no present-day theory of language can hope to attain explanatory adequacy beyond very restricted domains. In other words, we are very far from being able to present a system of formal and substantive linguistic universals that will be sufficiently rich and detailed to account for the facts of language learning. To advance linguistic theory in the direction of explanatory adequacy, we can attempt to refine the evaluation measure for grammars or to tighten the formal constraints on grammars so that it becomes more difficult to find a highly valued hypothesis compatible with primary linguistic data.