(3) The exercise of the faculty—let us call it x-ing—might be denied the title of perception because of its analogy with the having of sensations. It might be held that x-ing consisted in having some sort of experience generated by material things or events in the x-er's environment by way of some effect on his nervous system, though it did not qualify as perceiving the things or events in question. The kind of situation in which this view might be taken may perhaps be indicated if we consider the assaults made by physiologists and psychologists on the so-called "sense of touch." They wish, I think on neurological grounds, to distinguish three senses: a pressure-sense, a warm-and-cold sense, and a pain-sense. Would we be happy to accept their pain-sense as a sense in the way in which sight or smell is a sense? I think not; for to do so would involve regarding the fact that we do not

"externalizc" pains as a mere linguistic accident. That is to say, it would involve considering as unimportant the following facts: (a) that we are ready to regard "malodorous," as distinct from "painful" or "sharply painful," as the name of a relatively abiding characteristic which material things in general either possess or do not possess; we are as a general rule prepared to regard questions of the form "Is M (a material thing) malodorous? as being at Icast in principle answerable either affirmatively or negatively, whereas we should very often wish to reject questions of the form "Is M painful?" or "Is M sharply painful?"; and (b) that we speak of smells but not of pains as being in the kitchen.

Very briefly, the salient points here seem to me as follows:

1. Pains are not greatly variegated, except in intensity and loca-tion. Smells are.
2. There is no standard procedure for getting a pain: one can be cut, bumped, burned, scraped, and so on. There is a standard procedure for smelling, namely, inhaling.
3. Almost any type of object can inflict pain upon us, often in more than one way.

In consequence of these facts, our pains are on the whole very poor guides to the character of the things that hurt us. Particular kinds of smells, on the other hand, are in general characteristic of this or that type of object. These considerations I hope constitute a partial explanation of the fact that we do not, in general, attribute pain-qualities to things: we may in a special case speak of a thumbscrew, for ex-ample, as being a painful instrument, but this is because there is a standard way of applying thumbscrews to people. We do not speak of pains as being in (say) the kitchen; and the reason for this is, I think, that if a source of pain moves away from a given place, persons arriving in this place after the removal do not get hurt. Smells, on the other hand, do linger in places, and so are "de-tachable" from the material objects which are their source. Though pains do not linger in places, they do linger with individuals after the source of pain has been removed. In this again they are unlike smells.

I shall now turn to discussion of the second possible way of meeting the claim of x-ing to be the exercise of a new sense. This, you will remember, took the form of arguing that x-ing, though perceiving, is merely perceiving by one of the familiar senses, perhaps through an unfamiliar kind of sense-organ. At this point we need to ask by what criteria senses are to be distinguished from one another. The answer to this question, if obtainable, would tell us how x-ing must differ from the exercise of familiar senses in order to count as the operation of a distinct sense. Four seemingly independent ideas might be in-volved:

I. It might be suggested that the senses are to be distinguished by the differing features that we become aware of by means of them: that is to say, seeing might be characterized as perceiving (or seeming to perceive) things as having certain colors, shapes, and sizes; hearing as perceiving things (or better, in this case, events) as having certain degrees of loudness, certain determinates of pitch, certain tone-qualities; and so on for the other senses.

Il. It might be suggested that two senses, for example, seeing and smelling, are to be distinguished by the special introspectible character of the experiences of seeing and smelling; that is, disregarding the differences between the characteristics we learn about by sight and smell, we are entitled to say that seeing is itself different in character from smelling.

III. Our attention might be drawn to the differing general features of the external physical conditions on which the various modes of perceiving depend, to differences in the "stimuli" connected with different senses: the sense of touch is activated by contact, sight by light rays, hearing by sound waves, and so on.

IV. Reference might be made to the internal mechanisms associated with the various senses—the character of the sense-organs, and their mode of connection with the brain. (These suggestions need not of course be regarded as mutually exclusive. Itis possible-perhaps in