So far we have formulated only four rules. Now, having formulated the rules, we must include the words themselves in order to generate the sentence. Each category they involve—nouns, verbs, articles, prepositions—can be further expanded to include the words that constitute that category. Thus:
N → [cat, mouse, speed, yard . . .]
V → [chased . . .]
Art → [a(n), tfie]
Adj → [white, frightened, high, small, grassy . . .]
Prep → [at, into . . .]
You can easily see that a very great number of English sentences can be generated by means of this small set of rules, using the many other words that fit into the categories N, V, Adj, and Prep. (The category Art is different; there are only two articles in English—an being a variant of a.) However, if you consider sentences such as the following, you will also see that there is much more that must be accounted for in English sentences:
Whose mittens are these?
I disagree entirely.
I don't want you to go out tonight.
Let's see the crossword puzzle you have just finished.
Kenny told the girl who came to pick up the books that she couldn 't have them because he wasn 't finished reading them yet.
This will give you some idea of the vastness of the task of formulating the syntactic rules of a language—and we haven't even mentioned the rules for making the words sound right for the language or for constructing the words or for deriving "Jeet jet?' and 'No, joo?' from "Did you eat yet?" and "No, did you?"!
Let us look briefly at an example of unconscious rules of the sort Chomsky sought to formalize, drawn from the phonological component of your linguistic competence, that portion that deals with the sound system of your language. One example will suffice to indicate that the phonological component is also vast and complex. Sounds of a language that are identified by its speakers as being "the same," such as the two instances of the sound p in the English word paper, are in fact pronounced in a somewhat different manner and thus sound somewhat different. You can demonstrate this yourself quite easily. Hold a sheet of paper up to your lips as you pronounce the word paper; you will find that the first p carries with it a puff of air that blows the paper away from your lips, whereas the second p is said without this puff of air. Linguists refer to the puff of air as aspiration, calling the first p "aspirated" and the second one "unaspirated." The variation in their articulation depends on their position in the word: The sound p becomes aspirated when it occurs at the beginning of a syllable and is immediately followed by a stressed vowel (as in the first syllable of paper). When it is in any other position, it does not. Native English speakers never make the mistake of using one version where the other belongs. Yet they are generally unaware that they are using two versions of the sound. Thus we can speak of an underlying notion of the sound, which is stored in the speaker's brain as part of the pattern of speech sounds of his or her language. Just as water can exist as liquid (water), solid (ice), or gas (steam), so too are many of the sounds of language manifested differently in different environments, as the two versions of p in paper clearly show. The variants of a given sound, taken together, constitute a phoneme. A phoneme, then, is a kind of abstraction.
The sounds t and k are articulated in very much the same way as p—that is, without voice and by closing off the passageway in the mouth that allows the sound to be uttered on the expelled breath. (P does this at the lips, t with the tip of the tongue behind the top teeth, and k with the back part of the tongue touching the roof of the mouth. This can easily be demonstrated by simply saying the sounds.) All three of these sounds behave the same way, following the same rule with respect to aspiration. Following a convention that indicates aspiration by means of a superscript һ, it is possible to write a rule that expresses this situation:
p, t, k become pһ, tһ, kһ when they occur at the beginning of a syllable and are immediately followed by a stressed vowel.
By means of a set of symbols and terms that capture the commonalities among the three sounds, the conditions under which the rule is applied, and the result of its application, a very economical formal rule can be written. (To explain all the complications involved in arriving at such rules would require a course in linguistics. My purpose here is merely to suggest their complexity.)
The Relevance of the Rules to Cognitive Science
Perhaps your head is spinning from this discussion of the formalization of rules of English. Perhaps you are wondering why it was included. There are several reasons. First, to appreciate what was involved in the new linguistics of the 20th century, it is necessary to have at least some understanding of the turn it took in the direction of scientific inquiry and method. Second, establishing a formal means of encoding the rules of language enables important generalizations to be grasped (such as the one that extends the effect of the aspiration rule from one sound to all sounds made in the same manner). If we can capture in this way the rules that characterize languages, we can compare them to see what types of rules characterize human languages in general. From there we can proceed to a greater understanding of what the human brain is equipped with that enables it to "do" language.
Another reason for making the rules explicit is to increase our understanding of the" way children learn their first language. If it is indeed by means of acquiring such rules (however they are represented in the brain), we can more readily understand how it is possible for them to do it in the short time it actually takes.
Still another important reason to formalize the rules of language has to do with the capabilities we are developing, via the computer, to model aspects of human intelligence. Computer programs require very precise and unambiguous instructions. The formalization of the rules of language has enabled computer scientists involved in artificial intelligence to attempt to model human language on the computer.
Identifying and formalizing the rules of language rests on the assumption that they have been internalized, represented in some fashion in the brain — that they are in fact in there, somewhere. Regarding the issue from this perspective requires that we consider how it is possible for an infant to begin to acquire these rules, on the assumption that it is born not knowing them. This assumption is reasonable, because babies will learn to speak the languages spoken in their environment. (If a child is adopted by a family of a different culture from that of the biological parents, where a different language is spoken, the child learns the language of the adoptive culture.) We wonder, of course, how it is possible for the linguistic system of a given language to be absorbed, as it demonstrably is, early in childhood. Is the capacity to "do" language a specialized one, residing in brain functions evolved just for that purpose? Or is it rather, as some have proposed, one among many abilities that arise from certain general cognitive abilities, such as the ability to categorize experiences of our environment (this is a chair; that is a person; this word is a potential sentence subject, but that word can only designate an action)?