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Let us be clear, first, how Peirce distinguished abduction from induction and deduction, the other two logical components of the scientific method. He believed that neither deduction nor induction could arrive at explanatory theory but only abduction. No new truth can come from deduction or induction. Deduction explores the logical consequences of statements. Induction seeks to establish facts. Abduction starts from facts and seeks an explanatory theory (Peirce). As a classical example of abduction, Peirce cited Kepler’s theory of the elliptical form of Mars’s orbit. Though Kepler had made a large number of observations of the longitudes and latitudes of Mars, and even if he had made a million more, no induction or generalization from these facts could have arrived at the nature of Mars’s orbit. At some stage or other, Kepler had to make a guess, construct a model, then see if the model would (1) fit all the facts at hand and (2) predict new facts which could be verified by observation.

Peirce listed three kinds of abductions or explanatory hypotheses: (1) those which account for observed facts through “natural chance” or statistical methods, e.g., the kinetic theory of gases; (2) those which render the facts necessary through a mathematical demonstration of their truth, e.g., Kepler’s elliptical theory of planetary orbits; and (3) those which account for facts by virtue of the very economy and simplicity of the explanatory model (Peirce).

Presumably we are looking here for 3, at least for the present. Certainly no statistical method or mathematical model known to me has any relevance to what goes on inside a child’s head when he acquires language in the second and third year of life.

Peirce also makes much of the fact, and Chomsky echoes it, that “man’s mind has a natural adaptation to imagining correct theories” (Chomsky). A physicist comes across some new phenomenon in the laboratory. According to Peirce, there are “trillions of trillions of hypotheses” which might be made to account for it, “of which only one is true” (Peirce). Yet as matters usually turn out, the physicist usually hits on the correct hypothesis “after two or three or at the very most a dozen guesses.” This successful guessing or hypothesizing of scientists is not, according to Peirce, a matter of luck. Peirce’s own explanation of the extraordinary success (in the face of such odds) of scientific theorizing is founded in his own allegiance to philosophical realism, the belief that general principles actually operate in nature apart from men’s minds and that men’s minds are nevertheless capable of knowing these principles. But how is this possible? Peirce hazards the guess that, since “the reasoning mind is a product of the universe,” it is natural to suppose that the laws and uniformities that prevail throughout the universe should also be “incorporated in his own being” (Peirce).

Maybe so. This is only speculation, however interesting, about why abduction works. What concerns us here, entirely apart from Peirce’s philosophical realism and his explanation of it, is his theory of abduction itself, which I take to be nothing more nor less than the method of hypothesis formation as it is used in practice by scientists in general, whether one is theorizing about why volcanoes erupt or why people speak and animals don’t. Peirce’s theory of abduction, particularly of the third type, is both sufficiently rigorous that it achieves the level of explanatory adequacy and sufficiently nonspecific that it does not require a commitment to ideology and hence does not fall into the deterministic trap of behaviorism and learning theory. Explanatory theory at the level of the human acquisition of language, it seems fair to paraphrase Peirce, does not require a mechanism, or, in Peircean terms, a “dyadic” model.

I have taken the trouble to review Peirce’s theory of abduction both because of its possible value to linguistic theory and to call attention to the odd use to which Chomsky has put it.

Chomsky has revived Peirce’s theory of abduction, not in order to arrive at an explanatory theory of language, but rather to attribute the capacity for abduction to the child who acquires language. In the same way that, as Peirce speculated, man is somehow attuned to the rest of the universe so that he is able to theorize successfully about it, so it is that “knowledge of a language — a grammar — can be acquired only by an organism that is ‘preset’ with a severe restriction on the form of grammar.”

This innate restriction is a precondition, in the Kantian sense, for linguistic experience, and it appears to be the critical factor in determining the course and result of language learning. The child cannot know at birth which language he is to learn, but he must know that its grammar must be of a predetermined form that excludes many imaginable languages. Having selected a permissible hypothesis, he can use inductive evidence for corrective action, confirming or disconfirming his choice. (Chomsky)

What is odd of course is not Chomsky’s idea that language can only be learned by an organism “preset” with a severe restriction on the form of grammar — this squares very well with the suggestion made in this paper that all sentences in any language must take the form of a coupling made by a coupler — but rather Chomsky’s proposal to shift the burden of explanation from the linguist, the theorist of language as a phenomenon, to the child, the subject under study. Chomsky’s theory of language is that the child is capable of forming a theory of language.

Now Chomsky’s abdication may or may not be justified. Perhaps in the long run it will turn out that it is not possible to arrive at an explanatory theory of language in any ordinary sense of the word and that the only “explanation” available is that the child somehow hits on the grammar of a language after a fragmentary input. If this is so, we must face up to the fact that we have reverted to homunculus biology, explaining human potentialities both in spermatozoa and in children by supposing that each somehow has a little man locked inside. I believe, however, that by the serious use of abduction, hypothesis, not the attributing of it to the child but the figuring out of what goes on inside the head of a child, the theorist can hope to make a start toward the construction of a relatively simple and parsimonious model along Peircean lines.

It is curious to note in passing that if one is seeking philosophical progenitors for Peirce’s theory of abduction and the realism underlying his analysis of the scientific method, one is inevitably led not to Descartes and a mind-body dualism but, according to Peirce, to Duns Scotus!

7. Suppose one were to advance the following tentative hypothesis:

The basic and genetically prime component of the LAD is a semological-phonological device through which semological elements are coupled with phonological elements. Such linkages form a finite inventory of semological-phonological configurations or “semophones,” stable functional entities which correspond to semantically contentive words, e.g., wet, yellow, sock, knee. These semophones in turn become available for couplings to form a large number of “open-open” combinations, which are nothing less than primitive forms of the adult NP-VP sentence.

If this is the case, two questions arise: (1) Does such a model allow the possibility of looking for a neurophysiological correlate of the LAD — a possibility apparently disallowed by a basically syntactical model — and (2) if so, is there presently any evidence of such a correlate?

For some time I had supposed that the basic event which occurs when one utters or understands a sentence must be triadic in nature (Percy). That is to say, sentences comprise two elements which must be coupled by a coupler. This occurs in both the naming sentence, when semological and phonological elements are coupled, and in the standard declarative NP — VP sentence which comprises what one talks about and what one says about it.