（3）Certain specializations in peripheral anatomy and physiology account for some of the universal features of natural languages, but the description of these human peculiarities does not constitute an explanation for the phylogenetic development of language. During the evolutionary history of the species form function and behavior have interacted adaptively, but none of these aspects may be regarded as the ”cause” of the other. Today, mastery of language by an individual may be accomplished despite severe peripheral anomalies, indicating that cerebral function is now the determining factor for language behavior as we know it in contemporary man. This, however, does not necessarily reflect the evolutionary sequence of development events.
（4）The biological properties of the human form of cognition set strict limits to the range of possibilities for variations in natural languages. The forms and modes of categorization, the capacity for extracting similarities from physical stimulus configuration or from classes of deeper structural schemata, and the operating characteristics of the data-processing machinery of the brain (for example, time-limitations on the rate of input, resolution-power for the analysis of intertwined patterns such as nested dependencies, limits of storage capacities for data that must be processed simultaneously, etc.) are powerful factors that determine a peculiar type of form for language. Within the limits set, however, there are infinitely many variations possible. Thus the outer form of languages may vary with relatively great freedom, whereas the underlying type remains constant.
（5）The implication of（1）and（2）is that the existence of our cognitive processes entails a potential for language. It is a capacity for a communication system that must necessarily be of one specific type. This basic capacity develops ontogenetically in the course of physical maturation; however, certain environmental conditions also must be present to make it possible for language to unfold. Maturation brings cognitive processes to a state that we may call language-readiness. The organism now requires certain raw materials from which it can shape building blocks for his own language development. The situation is somewhat analogous to the relationship between nourishment and growth. The food that the growing individual takes in as architectural raw material must be chemically broken down and reconstituted before it may enter the synthesis that produces tissues and organs. The information on how the organs are to be structured does not come in the food but is latent in the individual’s own cellular components. The raw material for the individual’s language synthesis is the language synthesis is the language spoken by the adults surrounding the child. The presence of raw material seems to function like a releaser for the developmental language synthesizing process. The course of language-unfolding is quite strictly prescribed through the unique maturational path traversed by cognition, and thus we may say language-readiness is a state of latent language structure. The unfolding of language is a process of actualization in which latent structure is transformed into realized structure. The actualization of latent structure to realized structure is to give the underlying cognitively determined type a concrete form.*
* This formulation might be regarded …. (Do not omit footnote, p. 376)
（6）The actualization process is not the same as “beginning to say things.” In fact, it may be independent from certain restraints that are attending upon the capacity for making given responses. Actualization may take place even if responses are peripherally blocked; in this case actualization is demonstrable only through signs of understanding language. In cases where the proper raw material for language synthesis cannot be made available to the growing child（as in the deaf）,the latent structure fails to become actualized either temporarily or permanently.
（7）The maturation of cognitive processes comes about through progressive differentiation. Physiological（and, therefore, cognitive）functions assume characteristics and specificities much the way cells and tissues do during ontogeny. Organs do not suddenly begin to function out of a state of silence, but every function in the mature individual is a derivative of embryologically earlier types of function. Although the primitive functions may often be different from the mature ones, we cannot say just when a later or derived process had its beginning. If language is an aspect of a fundamental, biologically determined process, it is not scientifically profitable to look for a cause of language development in the growing child just as we do not look for a cause for the development of his ears. It might be more fruitful to think of maturation, including growth and the development of behavior such as language, as the traversing of highly unstable states; the disequilibrium of one leads to rearrangements that bring about new disequilibria, producing further rearrangements, and so on until relative stability, known as maturity, is reached. Language-readiness is an example of such a state of disequilibrium during which the mind creates a place into which the building blocks of language may fit.
（8）The disequilibrium state called language-readiness is of limited duration. It begins around two and declines with cerebral maturation in the early teens. At this time, apparently a steady state is reached, and cognitive processes are firmly structured, the capacity for primary language synthesis is lost, and cerebral reorganization of functions is no longer possible.
（9）The language potential and the latent structure may be assumed to be replicated in every healthy human being because they are consequence of human-specific cognitive processes and a human-specific course of maturation. In other words, universal grammar is of a unique type, common to all men, and it is entirely the by-product of peculiar modes of cognition based upon the biological constitution of individual. This notion of replication, which is a cornerstone of the present theory, also leads us to assume that the actualization process from latent to realized structure is universal because of replicated sequences of similar states of disequilibrium, and there is evidence for this assumption in the regularity of language-acquisition strategies discussed in Chapters Four and Seven.
（10）Because latent structure is replicated in every child and because all languages must have an inner form of identical type（although an infinity of variations is possible）, every child may learn any language with equal ease. The realized structure or outer form of the language that surrounds the growing child serves as mold upon which the form of child’s own realized structure is modeled. The maneuver is possible only because all languages are so constructed as to conform to the stringent requirements imposed upon them by cerebral language-data processing mechanisms. Insistence upon universal, underlying identity of type in all languages may be difficult to understand in the face of difference in rules of syntax and divergences. This puzzle is solved by considering the remarkable freedom allowed individual speakers to make creative and novel use of word-meanings, to reclassify words into various syntactic categories, and to take creative freedoms with rules of syntax. All aspects of outer form or realized structure are in a state of fluidity（of relatively high viscosity）indicating that it is our ”mode of calculating with categories” that is universal, but the categories themselves are not fixed nor the particular choice of the many possible operations.
（11）The raw material from which the individual synthesizes building blocks for his own language development cannot be the cause of the developing structure as evidenced by the autochthonous beginnings in the infant’s language acquisition. Primitive stages of language are simply too different from adult language to be regarded as a direct mirroring of the input. Nor is there any evidence that the adults surrounding the child are the causative or shaping agents that determine language onset or his course of development（see discussion of need as explanation in Chapter Four and of language teaching in Chapter Seven）. Purposiveness cannot, logically, be the mainspring for language development.