(University of Pennsylvania) (Bampton lectures in America 28) New York: Columbia University Press, 1988, ix+120 pp.

The glib freedom with which we use the word informa­tion would lead one to suppose we know what we are talking about. Alas, not so. In a field that concerns itself with "information processing", it is remarkable if not embarrassing that there is still, after 40 years, no generally accepted, coherent definition of information to underwrite the enterprise.

It is well known that information theory is not concerned with the information content or meanings of particular texts or utterances. It interprets certain mea­sures of probability or uncertainty in an ensemble of signal sequences (which may indeed be meaningless) as a metric of the difficulty of transmitting a given signal sequence, and then calls this metric, in a notoriously misleading way, the "amount of information" in the signal.

Carnap and Bar-Hillel announced long ago what was essentially a ramification of Carnap's work in inductive logic and probability, a Theory of Semantic Information dealing solely with linguistic entities ("state descrip­tions" in some logical language) and what they stand for or designate. Carnap's aim was to devise measures of "semantic content" that would enable him to get at "confirmation functions" to underwrite inductive logic. Bar-Hillel's initial enthusiasm was to develop a perhaps broader "calculus of information." Although the ban­ner they dropped was taken up in the '60s by Hintikka and others, it is safe to say that this line of thought has contributed little to a satisfactory definition of informa­tion.

Today, we witness the spectacle of Dretske and the situation semantics folks mounted precariously on the Scylla of naive realism, tilting with Fodor atop the Charybdis of a mental representationalism that is philo­sophically more sophisticated but no less ad hoc in its misuse of metaphor. Unfortunately, a summary of the well-deserved doubt that each casts upon the merits of the other's case is beyond the scope of this review.

The present book is a brief and very clear introduc­tion to a body of work that threads a naturalist path between these extremes and offers real insight into the nature of linguistic information. What is meant by this is the literal, objective information in discourse, as dis­tinct from, e.g., gestural systems such as expressive intonation and other body language. The paradigmatic case is a technical paper in a subfield of science, as opposed to artistic expressions, such as music, dance, and literary and poetic uses of language.

Harris shows how natural language differs in many important respects not only from such gestural systems on the one hand, but also from mathematics, logic, and formal languages, on the other. The formal structure of operators and arguments that Harris finds in language resembles functors of a categorial grammar in logic, but contrasts with them in a number of ways, including the following:

• Words are classified as operators and arguments not ostensively, by listing them, but with respect to the argument requirement of their arguments. This de­pendency on dependency, by virtue of which we recognize language to be a mathematical object (p. 89), makes possible the striking simplicity of the theory.

• Arguments of an operator may occur in various orders relative to each other (such as topicalization, fronting of a non-first argument), though in most languages there are one or two preferred sequences.

• An operator may enter at various points relative to its arguments as a sentence is constructed, though again the normal choices are limited in most languages.

• These alternative linearizations include interrup­tion—under a paratactic conjunction whose subordi­nating intonation is represented by a semicolon or, as here, by dashes—of a sentence by a secondary sen­tence. This is the origin in many languages of the relative clause and thence of all modifiers.

• Particular word combinations (operator-argument co­occurrences) are graded as to likelihood.

• Word occurrences that contribute little information (because of high likelihood) may occur in reduced phonemic form, even zero; conversely, occurrences with especially low likelihood may block otherwise customary reductions.

To see why approaches to information from the point of view of mathematical logic have been unable to get at intuitively appealing notions of information based upon our everyday use of natural language, we must see just how and why language "carries" information.

How can a formal theory of syntax—formal in that it defines entities by their frequency of occurrence rela­tive to each other rather than by their phonetic or semantic properties—have as its result (and indeed its point) an account of meaning? The answer lies in the well-known relation of information to redundancy or expectability. A central point is that there is no external metalanguage for the investigation of language, as there is for every other science. The information in language can be represented and explained only in language itself. All that is available for accomplishing this is to exploit the departures from randomness in language, first to distinguish its elements, and then to determine the structures (patterns of redundancy) in it. But it is precisely this redundancy among its elements that lan­guage itself uses for informational purposes: informa­tion is present in a text because the elements of lan­guage do not occur randomly with respect to each other.

For this reason, it is of critical importance that the description introduce no extrinsic redundancy: that it employ the fewest and simplest entities and the fewest and simplest rules, with (if possible) no repetition. The notorious complexity of grammar, most of which is created by the reductions, is not due to complexity in the information and is not needed for information (p.29).

[A]s we approach a least grammar, with least redundancy in the description of the structure, the connection of that grammar with information becomes much stronger. In­deed, the step-by-step connection of information with structure is found to be so strong as to constitute a test of the relevance of any proposed structural analysis of language. ... the components that go into the making of the structure are the components that go into the making of the information (p.57).Having arrived at a "least grammar", Harris shows us that a representation of the grammar of a text is also a representation of the information in it. For example, he shows us how analysis of texts in a science sublanguage yields what he calls a science language, "a body of canonical formulas, representing the science statements after synonymy and the paraphrastic reductions have been undone" (p.51). It is most striking that this repre­sentation of the information in technical articles is the same regardless of whether the original language was English, French, or some other language: its structure is a characteristic of the science and not of the particular natural language the investigators used for reporting their results and from which it was derived. Needless to say, this is a matter of some interest for machine translation, information retrieval, and knowledge representation.

The significant redundancy in language has two sources, two constraints on the equiprobability of word combinations.

• The first constraint, which creates sentence structure, is the partial ordering of operators with respect to their arguments. Its significance is, roughly, predica­tion: an operator is said "of its arguments.

• The second constraint, which specifies word mean­ings, is on the relative likelihood of particular con­structions of operator and argument words. As noted above, an operator-argument pair (which are always adjacent at time of entry—a matter of some compu­tational importance) may have exceptionally high

likelihood (low information), above average or "se-lectional" likelihood, lower likelihood, or exception­ally low likelihood.

As described above, words entering in the ongoing construction of a sentence are given a particular linear order. If with newly entering words a high-likelihood collocation arises, a reduction may (usually optionally) produce a more compact alternant form of the sentence. The reductions constitute a third constraint on co­occurrences of word shapes (allomorphs), but not one that contributes to information, since it is precisely low-information word occurrences that are affected." With both the alternant linearizations and the reductions, what changes is emphasis or ease of access to the objective information, which remains invariant. Nu­ances of meaning expressed by these means or by pauses, gesture, and so on, can also be expressed by using the above two "substantive" constraints in ex­plicit albeit perhaps more awkward language, as anyone knows who has puzzled out a joke or an "untrans­latable" idiom in a foreign language.

Every increment of information in a text corresponds to a step of sentence construction exercising one of these constraints. There is no a priori structure of information onto which grammar maps the spoken (or written) words of language: rather, the information in a text inheres in and is the natural interpretation of the structure of words that enables it to be expressed. Referring appears to be a matter of a loose correspon­dence between the redundancies in a text and similar departures from randomness in a set of events (pp. 83-85).

These are some of the chief themes of the first three lectures, entitled respectively "A Formal Theory of Syntax", "Science Sublanguages", and "Informa­tion". The fourth lecture, "The Nature of Language", is more far-ranging in content, discussing the structural properties of language, including language universals; language change and different aspects of language that are in greater or lesser degree subject to it; and stages and processes in the origin and development of language based upon the several contributory information-making constraints described earlier. In the final section on "Language as an Evolving System", Harris shows how language likely evolved and is evolving: "We may still be at an early stage of it" (p. 107).

In the closing pages, Harris responds to rationalist claims that complex, species-specific, innate biological structures are necessary for something as complex as language to be learnable, arguing that.

there is nothing magical about how much, and what, is needed in order to speak .... We can see roughly what kind of mental capacity is involved in knowing each contribution to the structure .... The kind of knowing that is needed here is not as unique as language seems to be, and not as ungraspable in amount.

The overall picture that we obtain is of a self-organizing system growing out of real-life conditions in combining sound sequences. Indeed, it could hardly be otherwise, since there is no external metalanguage in which to define the structure, and no external agent to have created it (pp. 112-113).

This book is a clear and succinct summation in compact form of an extensive body of scientific investigation that no one interested in either language or information can afford to ignore.