When I say that "inferences" are involved, I am saying something not quite accurate unless carefully interpreted. In "seeing a chair", for instance, we do not first apprehend a coloured pattern, and then proceed to infer a chair: belief in the chair arises spontaneously when we see the coloured pattern. But this belief has causes not only in the present physical stimulus, but also partly in past experience, partly in reflexes. In animals, reflexes play a very large part; in human beings, experience is more important. The infant learns slowly to correlate touch and sight, and to expect others to see what he sees. The habits which are thus formed are essential to our adult notion of an object such as a chair. The perception of a chair by means of sight has a physical stimulus which affects only sight directly, but stimulates ideas of solidity and so on through early experience. The inference might be called "physiological". An inference of this sort is evidence of past correlations, for instance between touch and sight, but may be mistaken in the present instance; you may, for example, mistake a reflection in a large mirror for another room. Similarly in dreams we make mistaken physiological inferences. We cannot therefore feel certainty in regard to things which are in this sense inferred, because, when we try to accept as many of them as possible, we are nevertheless compelled to reject some for the sake of self-consistency.
We arrived a moment ago at what we called "physiological inference" as an essential ingredient in the common-sense notion of a physical object. Physiological inference, in its simplest form, means this: given a stimulus S, to which, by a reflex, we react by a bodily movement R, and a stimulus S′ with a reaction R′, if the two stimuli are frequently experienced together, S will in time produce R′.[1] That is to say, the body will act as if S′ were present. Physiological inference is important in theory of knowledge, and I shall have much to say about it at a later stage. For the present, I have mentioned it partly to prevent it from
- ↑ E.g. if you hear a sharp noise and see a bright light simultaneously often, in time the noise without the light will cause your pupils to contract.
