While acknowledging that people—and many animals—do appear to act intelligently, eliminativists thought that they could account for this fact in nonmentalistic terms. For virtually the entire first half of the 20th century, they pursued a research program that culminated in B.F. Skinner’s (1904–90) doctrine of “radical behaviourism,” according to which apparently intelligent regularities in the behaviour of humans and many animals can be explained in purely physical terms—specifically, in terms of “conditioned” physical responses produced by patterns of physical stimulation and reinforcement (see also behaviourism; conditioning).

Radical behaviourism is now largely only of historical interest, partly because its main tenets were refuted by the behaviourists’ own wonderfully careful experiments. (Indeed, one of the most significant contributions of behaviourism was to raise the level of experimental rigour in psychology.) In the favoured experimental paradigm of a rigid maze, even lowly rats displayed a variety of navigational skills that defied explanation in terms of conditioning, requiring instead the postulation of entities such as “mental maps” and “curiosity drives.” The American psychologist Karl S. Lashley (1890–1958) pointed out that there were, in principle, limitations on the serially ordered behaviours that could be learned on behaviourist assumptions. And in a famously devastating critique published in 1957, the American linguist Noam Chomsky demonstrated the hopelessness of Skinner’s efforts to provide a behaviouristic account of human language learning and use.

Since the demise of radical behaviourism, eliminativist proposals have continued to surface from time to time. One form of eliminativism, developed in the 1980s and known as “radical connectionism,” was a kind of behaviourism “taken inside”: instead of thinking of conditioning in terms of external stimuli and responses, one thinks of it instead in terms of the firing of assemblages of neurons. Each neuron is connected to a multitude of other neurons, each of which has a specific probability of firing when it fires. Learning consists of the alteration of these firing probabilities over time in response to further sensory input.

Few theorists of this sort really adopted any thoroughgoing eliminativism, however. Rather, they tended to adopt positions somewhat intermediate between reductionism and eliminativism. These views can be roughly characterized as “irreferentialist.”

Wittgenstein

It has been noted how, in relation to introspection, Wittgenstein resisted the tendency of philosophers to view people’s inner mental lives on the familiar model of material objects. This is of a piece with his more general criticism of philosophical theories, which he believed tended to impose an overly referential conception of meaning on the complexities of ordinary language. He proposed instead that the meaning of a word be thought of as its use, or its role in the various “language games” of which ordinary talk consists. Once this is done, one will see that there is no reason to suppose, for example, that talk of mental images must refer to peculiar objects in a mysterious mental realm. Rather, terms like thought, sensation, and understanding should be understood on the model of an expression like the average American family, which of course does not refer to any actual family but to a ratio. This general approach to mental terms might be called irreferentialism. It does not deny that many ordinary mental claims are true; it simply denies that the terms in them refer to any real objects, states, or processes. As Wittgenstein put the point in his Philosophische Untersuchungen (1953; Philosophical Investigations), “If I speak of a fiction, it is of a grammatical fiction.”

Of course, in the case of the average American family, it is quite easy to paraphrase away the appearance of reference to some actual family. But how are the apparent references to mental phenomena to be paraphrased away? What is the literal truth underlying the richly reified façon de parler of mental talk?

Although Wittgenstein resisted general accounts of the meanings of words, insisting that the task of the philosopher was simply to describe the ordinary ways in which words are used, he did think that “an inner process stands in need of an outward criterion”—by which he seemed to mean a behavioral criterion. However, for Wittgenstein a given type of mental state need not be manifested by any particular outward behaviour: one person may express his grief by wailing, another by somber silence. This approach has persisted into the present day among philosophers such as Daniel Dennett, who think that the application of mental terms cannot depart very far from the behavioral basis on which they are learned, even though the terms might not be definable on that basis.

Ryle and analytical behaviourism

Some irreferentialist philosophers thought that something more systematic and substantial could be said, and they advocated a program for actually defining the mental in behavioral terms. Partly influenced by Wittgenstein, the British philosopher Gilbert Ryle (1900–76) tried to “exorcize” what he called the “ghost in the machine” by showing that mental terms function in language as abbreviations of dispositions to overt bodily behaviour, rather in the way that the term solubility, as applied to salt, might be said to refer to the disposition of salt to dissolve when placed in water in normal circumstances. For example, the belief that God exists might be regarded as a disposition to answer “yes” to the question “Does God exist?”

A particularly influential proposal of this sort was the Turing test for intelligence, originally developed by the British logician who first conceived of the modern computer, Alan Turing (1912–52). According to Turing, a machine should count as intelligent if its teletyped answers to teletyped questions cannot be distinguished from the teletyped answers of a normal human being. Other, more sophisticated behavioral analyses were proposed by philosophers such as Ryle and by psychologists such as Clark L. Hull (1884–1952).

This approach to mental vocabulary, which came to be called “analytical behaviourism,” did not meet with great success. It is not hard to think of cases of creatures who might act exactly as though they were in pain, for example, but who actually were not: consider expert actors or brainless human bodies wired to be remotely controlled. Indeed, one thing such examples show is that mental states are simply not so closely tied to behaviour; typically, they issue in behaviour only in combination with other mental states. Thus, beliefs issue in behaviour only in conjunction with desires and attention, which in turn issue in behaviour only in conjunction with beliefs. It is precisely because an actor has different motivations from a normal person that he can behave as though he is in pain without actually being so. And it is because a person believes that he should be stoical that he can be in excruciating pain but not behave as though he is.

It is important to note that the Turing test is a particularly poor behaviourist test; the restriction to teletyped interactions means that one must ignore how the machine would respond in other sorts of ways to other sorts of stimuli. But intelligence arguably requires not only the ability to converse but the ability to integrate the content of language into the rest of one’s psychology—for example, to recognize objects and to engage in practical reasoning, modifying one’s behaviour in the light of changes in one’s beliefs and preferences. Indeed, it is important to distinguish the Turing test from the much more serious and deeper ideas that Turing proposed about the construction of a computer; these ideas involved an account not merely of a system’s behaviour but of how that behaviour might be produced internally. Ironically enough, Turing’s proposals about machines were instances not of behaviourism but of precisely the kind of view of internal processes that behaviourists were eager to avoid.