On explaining language.

form of description, not of scattered facts but of the dynamic interrelations-the operating principlesfound in nature. Chomsky and his students have done this. Their aim has been to develop algorithms for specific languages, primarily English, that make explicit the series of computations that may account for the structure of sentences. The fact that these attempts have only been partially successful is irrelevant to the argument here. (Since every native speaker of English can tell a well-formed sentence from an illformed one, it is evident that some principles must exist; the question is merely whether the Chomskyites have discovered the correct ones.) The development of algorithms is only one province of mathematics, and in the eyes of many mathematicians a relatively limited one. There is a more exciting prospect; once we know sornething about the basic relational operating principles underlying a few languages, it should be possible to characterize formally the abstract system language as a whole. If our assumption of the existence of basic, structural language universals is correct, one ought to be able to adduce rigorous proof for the existence of homeomorphisms between any natural languages, that is, any of the systems characterized formally. If a category calculus were developed for this sort of thing, there would be one level of generality on which a common denominator could be found; this may be done trivially (for instance by using the product of all systems). However, our present knowledge of the relations, and the relations of relations, found in the languages so far investigated in depth encourages us to expect a significant solution. Environment and Maturation Everything in life, including behavior and language, is interaction of the individual with its milieu. But the milieu 9 MAY 1969 is not constant. The organism itself helps to shape it (this is true of cells and organs as much as of animals and man). Thus, the organism and its environment is a dynamic system and, phylogenetically, developed as such. The development of language in the child may be elucidated by applying to it the conceptual framework of developmental biology. Maturation may be characterized as a sequence of states. At each state, the growing organism is capable of accepting some specific input; this it breaks down and resynthesizes in such a way that it makes itself develop into a new state. This new state makes the organism sensitive to new and different types of input, whose acceptance transforms it to yet a further state, which opens the way to still different input, and so on. This is called epigenesis. It is the story of embryological development observable in the forniation of the body, as well as in certain aspects of behavior. At various epigenetic states, the organism may be susceptible to more than one sort of input-it may be susceptible to two or more distinct kinds or even to an infinite variety of inputs, as long as they are within determined limits-and the developmental history varies with the nature of the input accepted. In other words, the organism, during development, comes to crossroads; if condition A is present, it goes one way; if condition B is present, it goes another. We speak of states here, but this is, of course, an abstraction. Every stage of maturation is unstable. It is prone to change into specific directions, but requires a trigger from the environment. When language acquisition in the child is studied from the point of view of developmental biology, one makes an effort to describe developmental stages together with their tendencies for change and the conditions that bring about that change. I believe that the schema of physical maturation is applicable to the study of language development because children appear to be sensitive to successively different aspects of the language environment. The child first reacts only to intonation patterns. With continued exposure to these patterns as they occur in a given language, mechanisms develop that allow him to process the patterns, and in most instances to reproduce them (although the latter is not a necessary condition for further development). This changes him so that he reaches a new state, a new potential for language development. Now he becomes aware of certain articulatory aspects, can process them and possibly also reproduce them, and so on. A similar sequence of acceptance, synthesis, and state of new acceptance can be demonstrated on the level of semantics and syntax. That the embryological concepts of differentiation, as well as of determination and regulation, are applicable to the brain processes associated with language development is best illustrated by the material discussed above under the headings "brain correlates" and "critical age for language acquisition." Furthermore, the correlation between language development and other maturational indices suggests that there are anatornical and physiological processes whose maturation sets the pace for both cognitive and language development; it is to these maturational processes that the concept differentiation refers. We often transfer the meaning of the word to the verbal behavior itself, which is not unreasonable, although, strictly speaking, it is the physical correlates only that diffe~entiate.