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.”
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?
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Literary Characters: Fact or Fiction?
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 philo