The Basic Property of Human Language: A Computational System for Thought and Communication | Apuntes de Morfología y Sintaxis

The Galilean Challenge: Architecture and Evolution of Language To cite this article: Noam

Chomsky 2017 J. Phys.: Conf. Ser. 880 012015 View the article online for updates and

enhancements https://doi.org/10.1088/1742-6596/880/1/012015

it becomes possible to formulate what we may call the Basic Property of human

language: the language faculty of the human brain provides the means to construct a

digitally infinite array of structured expressions, each of which has a semantic

interpretation expressing a thought, and each of which can be externalized by means

of some sensory modality. The infinite set of semantically interpreted objects

constitutes what has sometimes been called a language of “thought”: the system of

thoughts that receive linguistic expression and that enter into reflection, inference,

planning, and other mental processes, and when externalized can be used for

communication and other social interactions. We may fairly assume that the language

faculty is shared among humans. There are no known group differences in language

capacity, and individual variation is at the margins.

The fundamental task of inquiry into language is to determine the nature of the Basic

Property. To the extent that its properties are understood, we can seek to investigate

particular internal languages, each an instantiation of the Basic Property, much as each

individual visual system is an instantiation of the human faculty of vision. We can

investigate how the internal languages are acquired and used, how the language

faculty itself evolved, its basis in human genetics and the ways it functions in the

human brain. This general program of research has been called the Biolinguistic

Program. The theory of the genetically based language faculty is called Universal

Grammar; the theory of each individual language is called its Generative Grammar.

The Basic Property takes language to be a computational system, which we therefore

expect to observe general conditions on computational efficiency. A computational

system consists of a set of atomic elements and rules to construct more complex ones.

For generation of the language of thought, the atomic elements are word-like, though

not words; for each language, the set of these elements is its lexicon. The lexical items

are commonly regarded as cultural products, varying widely with experience and

linked to extra-mental entities – an assumption expressed in the titles of standard

works, such as W.V. O. Quine’s influential study Word and Object. Closer examination

reveals a very different picture, one that poses many mysteries. Let’s put that aside for

now, turning to the computational procedure.

Linguistics has an additional motive of its own for seeking the simplest theory: it must

face the problem of evolvability. Not a great deal is known about evolution of modern

humans, but the few facts that are well established, and others that have recently

been coming to light, are rather suggestive, and conform well to the conclusion that

the language faculty is near optimal for a computational system, the goal we should

seek on purely methodological grounds. One fact that does appear to be well

established I have already mentioned: that the faculty of language is a true species

property, invariant among human groups – and, furthermore, unique to humans in its

essential properties. It follows that there has been little or no evolution of the faculty

since human groups separated from one another. Recent genomic studies place this

date not very long after the appearance of anatomically modern humans about

200,000 years ago, perhaps some 50,000 years later, when the San group in Africa

separated from other humans. There is no evidence of anything like human language,

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The Galilean Challenge: Architecture and Evolution of Language To cite this article: Noam Chomsky 2017 J. Phys.: Conf. Ser. 880 012015 View the article online for updates and enhancements https://doi.org/10.1088/1742-6596/880/1/

it becomes possible to formulate what we may call the Basic Property of human language: the language faculty of the human brain provides the means to construct a digitally infinite array of structured expressions, each of which has a semantic interpretation expressing a thought, and each of which can be externalized by means of some sensory modality. The infinite set of semantically interpreted objects constitutes what has sometimes been called a language of “thought”: the system of thoughts that receive linguistic expression and that enter into reflection, inference, planning, and other mental processes, and when externalized can be used for communication and other social interactions. We may fairly assume that the language faculty is shared among humans. There are no known group differences in language capacity, and individual variation is at the margins. The fundamental task of inquiry into language is to determine the nature of the Basic Property. To the extent that its properties are understood, we can seek to investigate particular internal languages, each an instantiation of the Basic Property, much as each individual visual system is an instantiation of the human faculty of vision. We can investigate how the internal languages are acquired and used, how the language faculty itself evolved, its basis in human genetics and the ways it functions in the human brain. This general program of research has been called the Biolinguistic Program. The theory of the genetically based language faculty is called Universal Grammar ; the theory of each individual language is called its Generative Grammar. The Basic Property takes language to be a computational system, which we therefore expect to observe general conditions on computational efficiency. A computational system consists of a set of atomic elements and rules to construct more complex ones. For generation of the language of thought, the atomic elements are word-like, though not words; for each language, the set of these elements is its lexicon. The lexical items are commonly regarded as cultural products, varying widely with experience and linked to extra-mental entities – an assumption expressed in the titles of standard works, such as W.V. O. Quine’s influential study Word and Object. Closer examination reveals a very different picture, one that poses many mysteries. Let’s put that aside for now, turning to the computational procedure. Linguistics has an additional motive of its own for seeking the simplest theory: it must face the problem of evolvability. Not a great deal is known about evolution of modern humans, but the few facts that are well established, and others that have recently been coming to light, are rather suggestive, and conform well to the conclusion that the language faculty is near optimal for a computational system, the goal we should seek on purely methodological grounds. One fact that does appear to be well established I have already mentioned: that the faculty of language is a true species property, invariant among human groups – and, furthermore, unique to humans in its essential properties. It follows that there has been little or no evolution of the faculty since human groups separated from one another. Recent genomic studies place this date not very long after the appearance of anatomically modern humans about 200,000 years ago, perhaps some 50,000 years later, when the San group in Africa separated from other humans. There is no evidence of anything like human language,

or symbolic activities altogether, before the emergence of modern humans. That leads us to expect that the faculty of language emerged along with modern humans or not long after, a very brief moment in evolutionary time. It follows, then, that the Basic Property should indeed be very simple. The conclusion conforms to what has been discovered in recent years about the nature of language, a welcome convergence. The discoveries about early separation of the San people are highly suggestive. They appear to share the general human language capacity, but have significantly different externalized languages. With irrelevant exceptions, their languages are all and only the languages with phonetic clicks, with corresponding adaptations in the vocal tract. The most likely explanation for these facts, developed in detail in current work by Dutch linguist Riny Huijbregts,4 is that possession of internal language preceded separation, which in turn preceded externalization, the latter in somewhat different ways in separated groups. Externalization seems to be associated with the first signs of symbolic behavior in the archaeological record, after the separation. Putting these observations together, it seems that we are reaching a stage in understanding where the account of evolution of language can perhaps be fleshed out in ways that were unimaginable until quite recently. Returning to the Basic Property, as we have seen we have reason to believe that it may be quite simple. The challenge for research, then, is to show how the facts of language are accounted for in terms of the Basic Property: more fully, by the interaction of the Basic Property, specific experience, and language-independent principles, including principles of computational efficiency. The challenge is of particular interest and significance when it is clear that the child’s experience provides little or no relevant evidence – a situation far more prevalent than commonly realized, so careful examination reveals, from acquisition of word meaning on to syntactic structures and the semantic properties of the generated language of thought. Also of particular interest are the universal properties of the language faculty that began to come to light as soon as serious efforts were undertaken to construct generative grammars, including quite simple principles that had never been noticed, and that are quite puzzling. One crucial and puzzling principle is structure-dependence: the rules that yield the language of thought attend solely to structural properties, ignoring properties of the externalized signal, even such simple properties as linear order. The property is illustrated by elementary examples. Consider the sentence “John and his father are tall” – not is tall, though the bigram frequency of father-is is much greater than of father-are, and the computation using linear order (adjacency) is far simpler than the computation that has to analyze the sentence into phrases and use phrasal locality. To take an example of semantic construal, consider the sentence birds that fly instinctively swim. It is ambiguous: the adverb “instinctively” can be associated with the preceding verb (fly instinctively) or the following one (instinctively swim). Suppose now that we extract the adverb from the sentence, forming instinctively, birds that fly swim. Now the ambiguity is resolved: the adverb is construed only with the linearly more remote but structurally closer verb swim, not the linearly closer but structurally more remote verb fly. The only possible interpretation – birds swim – is the unnatural one, but that doesn’t matter: the rules apply rigidly, independent of meaning and fact. What is puzzling, again, is that the rules ignore the simple computation of linear distance and keep to the far more complex computation of structural distance. The principle of structure dependence holds for all constructions in

properties of language follow directly from this assumption, along with a few other quite simple ones. One important result has to do with the property of displacement, a ubiquitous and also quite puzzling property of language: phrases are heard in one position but interpreted both there and in some other position that is silent but where they could have occurred – a puzzling property, which is never built into artificial symbolic systems for metamathematics, programming, or other purposes. For example, the sentence “which book will you read?” is interpreted as meaning roughly: “for which book x, you will read the book x,” with the nominal phrase book heard in one position but interpreted in two positions. I will not go into the details, but it is easy to show that Merge-based computation automatically yields displacement with copies; in this case, two copies of which book, yielding the correct semantic interpretation directly. The same process yields quite intricate semantic interpretations, and also has significant implications about the nature of language. To see why, consider for example the sentence “the boys expect to see each other” and the same sentence preceded by “which girls”: “which girls do the boys expect to see each other.” In the latter sentence, “each other” does not refer back to the closest antecedent, “the boys,” as such phrases universally do, but rather to the more remote antecedent “which girls.” The sentence means “for which girls the boys expected those girls to see each other.” That is what reaches the mind, under Merge-based computation with automatic copies, though not what reaches the ear. What reaches the ear violates the locality condition of referential dependency. Deletion of the copy in externalization causes processing problems: such filler-gap problems, as they are called, can be become quite severe, and are among the major problems of automatic parsing and perception. If the copy were not deleted, the problem would not arise. Why then is it deleted? Again, because of principles of efficient computation that reduce what is computed to the minimum: at least one copy must appear or there is no evidence that displacement took place at all, so only the structurally most prominent one remains (with important qualifications strengthening the conclusion, which I will put aside), leaving a gap that must be filled by the hearer – a matter that can become quite intricate. These examples illustrate a general phenomenon of some significance. Language design appears to maximize computational efficiency but disregards communicative efficiency. In fact, in every known case in which computational and communicative efficiency conflict, communicative efficiency is ignored. These facts argue against the common belief that communication is the basic function of language. They also further undermine continuity assumptions about language evolving from animal communication. And they provide further evidence that externalization, which is necessary for communication, is a peripheral aspect of language. As I mentioned, there are methodological reasons and also some evolutionary reasons to expect that the basic design of language will be quite simple, perhaps even close to optimal. With regard to externalization of language, the same methodological arguments hold, but the evolutionary arguments do not apply. In fact, externalization of language may not involve evolution at all. The sensorimotor systems were in place long before the appearance of language. Mapping the internal language to some sensorimotor system for externalization is a hard cognitive problem, relating two systems that are unrelated: an internal system that may be highly efficient computationally, and a sensory modality unrelated to it. That would lead us to expect

that the variety, complexity, and easy mutability of observed languages might lie primarily in externalization. Increasingly, it seems clear that that is the case. And in fact it should be expected, since the principles of the internal language are largely known by children without evidence, as, indeed, is a great deal more about language, including almost all semantic and most syntactic properties – a matter of contention, but solidly established, I think. Let us return finally to the second component of a computational system, the atomic elements: for language, the lexical items. As I mentioned, the conventional view is that these are cultural products, and that the basic ones – those used for referring to the world – are associated with extra-mental entities. This representationalist doctrine has been almost universally adopted in the modern period. The doctrine does appear to hold for animal communication: a monkey’s calls, for example, are associated with specific physical events. But the doctrine is radically false for human language, as was recognized as far back as classical Greece.

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