The Causal Theory of Perception John Watling
I should like to comment on Mr. A. C. Lloyd’s argument that the refutation of the Causal Theory of perception is only valid when a sense-datum language is assumed. ‘When Ayer, for example, calls the theory logically untenable all he means to do is to object to a causal argument from sense-data to things which are not sense- data.’ That is, to expand this statement of the argument : if statements about physical objects or the function of the nervous system are based only on sense-datum statements then all that can be said in this way is that certain concatenations of sense-data cause certain other concatenations. To speak of something that is not a sense-datum causing a sense-datum is meaningless, indeed impossible in this language. This argument involves the statement of the causal theory of perception being in a language whose sentences are reducible to sentences about sense-data. Lloyd’s thesis is that a sense-datum language is not logically necessary and that all that is necessary is the specification, in a particular language, of those statements which are to be correctors. One standard that he gives for making this choice of correctors is ‘suitability to modern scientific method’. This choice of correctors amounts to a choice of language; unfortunately it also has the effect of ossifying scientific method. The refutation of the causal theory of perception has been given in a language where the correctors are sense-datum statements. Suppose we now choose our correctors differently and take the statements of physiology as correctors; that is we consider such statements as incorrigible by other statements and, consequently, as logically independent of other statements. The statements of sense perception, however, we will suppose corrigible, that is based on other statements including those of physiology. But if the sense perception statements are based on those of physiology, then, quite parallel with the previous refutation, there follows a refutation of the causal theory of perception. For all that can be said in this language is that certain physiological events cause other physiological events. These ‘refutations’ of the causal theory of perception amount to no more than showing that, once the correctors have been chosen in a certain way, then the theory is no longer statable in that language. Suppose, then, that we attempt to construct a language in which the theory will be statable. To do this we must choose our correctors so that both the antecedent and the consequent of the causal law will have independent meanings. The correctors must be chosen so that, whether the statements of physiology or of sense perception are all correctors or not, they are based on independent sets of correctors. No sense perception statement must be corrected by a corrector which also corrects a
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physiological statement given this choice of correctors for our language we can state a causal law about physiological events causing perceptions and not mean merely that physiological events cause physiological events or perceptions cause perceptions. Not only can the causal theory be stated in this language; but it is non-contradictory and verifiable, providing that we concede that physiological statements are known by some other means than perception. If the term ‘sense-perception’ was limited to auditory experiences then it is easy to imagine physiological statements verified independently of auditory experiences and this is an example of a non- contradictory but limited form of the causal theory. But if sense perception is tacitly supposed to be the only source of knowledge, or at least the only source relevant to physiology and physical objects, then the statement of the causal theory must be completed by the addition, ‘only statements of sense perception are correctors’. And if this supposition is not made then we have not got an explanation of perception in terms of what is not perceived, we have not got the causal theory of perception. Then, if the causal theory is stated in the language which provides that physiological and perceptual statements are corrected independently, we must add to the rules specifying the correctors another rule in contradiction with some of them. So the causal theory of perception cannot be stated in any of the three types of language considered and these three types are exhaustive. The reason is that the statement of the causal theory, if it is to mean what it has been thought to mean, must be made in a language in which physiological statements are both corrected and uncorrected, both dependent on sense perception statements and independent of them. This argument does not require that a statement should say of itself that it is a corrector; it only requires that, for the meaning of a statement to be complete, the correctors for the language in which it is made be given. The attempts to state the causal theory in different languages exemplifies this. If it is true in general then the choice of correctors determines not only the language we use, but also what we say.
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