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The argument from illusion

University of British Columbia

It has often been alleged that the argument from illusion demonstrates that perceptual judgements expressed in ordinary or material object language are inherently vulnerable to scepticism, are imprecise, ambiguous, inconvenient, and imply somewhat more than we legitimately ought to say. Perceptual judgements about the same experience expressed in sense data language are, on the other hand, allegedly shown to be indubitable, precise, unambiguous, and, as such, to be the raw data from which our empirical knowledge is inferred. I contend there is no such essential asymmetry between an object language judgement (M-judgement) and a sense data language judgement (S-judgement) about the same perceptual experience provided the judgements are intended to have the same function. Arguments from illusion are, I contend, arguments by analogy. They argue that since we may be subject to illusion, then perhaps we are presently subject to illusion. But arguments by analogy are less arguments than hypotheses. We can easily counter that since we may not be subject to illusion, perhaps we are not presently subject to illusion. The problem is to discover whether or not we are subject to illusion and this, in principle we can do. M-judgements, as contingent judgements, can only be held to be contingently doubtful; they may in principle be verified or falsified. Further, if we attend closely to the conditions under which we make M-judgements and to our pragmatic interests and purposes in making them, we discover that such dubitability to which they are prone derives essentially from the fact that they are intended to effect a maximum differentiation of our sensory experience. S-judgements on the other hand are shown to derive their indubitability proportionately to the extent that they minimize differentiation of our experience. Indubitability is achieved only by diminishing the risk of contingency entailed by classifying experience. A completely doubt-free S-judgement then, would effect minimal differentiation of sensory experience and considering our pragmatic interests, would be singularly inutile. Thus it has been shown that such advantages as S-judgements have over M-judgements with respect to doubt derive only from a more radical asymmetry of intention, function, and utility. Further asymmetries regarding precision, ambiguity and convenience are shown either to be similarly untenable or to favor M-language. My conclusions are meant to undermine the tradition of basing sense data philosophy upon an inferiority of ordinary (M-statement) language as allegedly shown by a problematic asymmetry of M-judgements with S-judgements. No such troublesome asymmetry exists. I do recognize that arguments from illusion elucidate the extent to which ordinary language reflects conditions that are purely contingent and that it may well be possible to establish independently a sense data language which is less tied to purely contingent empirical conditions.

Text

2011-07-04

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http://hdl.handle.net/2429/35869

Philosophy

University of British Columbia

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