I understand by a sensation simply an experience of a non-propositional, non-appetitive character. (For these terms, see further below.) We are normally aware of our sensations, and so we believe that we are having them while we are having them. Normally, while a person is having an after-image, he is aware of having it. But, for reasons which I shall give later, I am not making it a matter of definition that a subject must be aware of a sensation while he has it. I shall argue only that he must be aware of some of the conscious episodes which he is currently having. A sensation can however only escape a subject's notice through being swamped, as it were, by other sensations, thoughts, and purposings. Also, I suggest, one thing which is involved in a sensation being part of a state of consciousness is that (whether or not with privileged access) a subject must be able to be aware of any current sensation if he chooses to consider which sensations he is having. An after-image wouldn't be an experience, a sensation, or an after-image if the subject was unable to become aware that he was currently having it.
Like all experiences, sensations are passive in the sense that they happen to the subject, they are experienced by him; they do
not consist of his bringing something about. But although they do not consist of the subject bringing something about, they are subject to different degrees of voluntary control. Which mental images I have is often to a considerable degree up to me; and many of the sensations which are caused in me by the outside world are ones which I can shut off (e.g. by closing my eyes). Pains, however, by contrast are often unavoidable. Sensations are non-propositional in the sense that they do not consist in an attitude to a state of affairs under a description. They may occur without being conceptualized by the subject. This can be seen by the fact that to the extent that some proposition describes a sensation, any logically equivalent proposition will do so equally correctly. A pattern of dots in a subject's visual field described as four rows of three dots, may be described equally correctly as three columns of four dots, or as a pattern of dots in the shape of a rectangle with one side of two-thirds the length of the other. The subject may know that some of these descriptions apply to his sensation, and not know that others do, but he will not think of any one of these descriptions as in any way picking out the essence of the sensation in a way that the others do not. Sensations, as I am understanding the term, are non-appetitive, that is do not involve any element of desire. I thus distinguish the sensory component of a sweet taste from the desire to continue to enjoy it.
Paradigm cases of sensations exemplifying this definition include the experiencings of patterns of colour (when the subject has no belief that they correspond to anything in the outside world), such as the having of after-images, eidetic memory images, lines in the visual field symptomatic of migraine, images had by the drink- or drug-addict; the hearing of noises ‘in the head’, smelling a smell of roses, or tasting a taste of honey (where the subject does not believe that there are roses or honey present). It seems fairly evident (although I shall argue for this briefly later) that one element in perception is very similar to, and sometimes indistinguishable from, the above sensations, and hence also to be termed sensation. Experiencing of the patterns of colour which the subject does not believe to be the surfaces of public objects is very similar to experiencing patterns of colour which the subject does believe to be the surfaces of public objects; tasting a taste of honey when you do not believe that there is honey in your mouth is very like tasting a taste of honey when you do have this belief—except
that in the latter cases there is something else mental present, the belief. Other examples of sensations are feeling bodily sensations, such as pains, itches, tickles, heat, and cold minus any desire which accompanies them. Experiences of certain kinds are so regularly accompanied by the desire that the experience cease, that we tend to make it part of the concept of an experience of those kinds that the subject desire not to have it. In one sense of ‘pain’, a pain would not be a pain unless it was unpleasant, i.e. the subject desired not to have it. But one can distinguish between the sensation and the desire in all of these cases. One can see the distinction in the case of pain by noting that a normal pain is a more acute feeling of a kind which would not be unpleasant in a very mild degree.12 The mildest of pricks or
aches is not unpleasant. Note also that when those suffering acute pain are subjected to the brain operation of prefrontal leucotomy, they sometimes report that although the ‘pain’ is still there, it is no longer unpleasant.13
Into the class of sensations come also the faint and blurred schematic copies of sensations of the central kinds which I have discussed, in the form of memory images (when memory comes to one via images) and the intentionally imaged diagrams or patterns of the imagination. Such is the class of the sensory. My examples of sensations should elucidate the sense of ‘experience’ in which sensations are experiences.
A person having a sensation is an event of a substance (the person) being characterized by a monadic property. My having a red image is my having a property (having-a-red-image). It is not my having a relation (experiencing) to some second substance (a red image). Although we are not tempted to analyse the having of certain kinds of sensations in this way—no one would suppose that
12 See R. M. Hare, ‘Pain and Evil’, Proceedings of the Aristotelian Society, Supplementary Volume, 1964, 38, 91–106 . Reprinted in (ed.) J. Feinberg, Moral Concepts, Oxford
University Press, London, 1969 . And for full-length development of the distinction between the sensation of pain and any other elements involved with what we normally call ‘pain’; the fact that some sensations other than pains are unpleasant; and the fact that although many sensations are pleasurable (i.e. we desire to have them), there is no sensation of pleasure corresponding to the sensation of pain, see R. Trigg, Pain and Emotion, Clarendon Press, Oxford, 1970.
13 Not all cases of the lessening of concern for ‘pain’ resulting from pre-frontal leucotomy are to be given the interpretation that the ‘pain’ i.e. the sensation, has remained at the
having a headache was experiencing a thing—we are so tempted in other cases. Having a visual image, and especially an eidetic image (i.e. the very detailed image of an object, say the page of a book, which some people retain after looking away from the object), is more naturally thought of as experiencing a thing, a ‘sense-datum’. The image seems something external to ourselves which we inspect. Although it is important to bring out that some sensations have this character of being an experience of something apparently external, it is equally important to emphasize that there is in fact no external substance to which we are related when we have such sensations. For if a sense-datum were a substance, it would have to be capable of independent existence—of existing unsensed and then being sensed now by you, and now by me. But if a sensedatum were in this way a public thing, it would be no more a component of sensation than my desk is a component of the visual sensation to which it gives rise when I look at it. One way of making the point that having a sensation is being characterized by a monadic property is what is known as the ‘adverbial’14account of sensation, which recommends that the property of having a red image should be characterized
less misleadingly as the property of ‘being appeared to redly’.