I intend to call this class of entities the class of _sensibles_; so that the question I am to discuss can be expressed in the form: What is the status of sensibles? And it must be remembered that images and after-images are just as much "sensibles," in my sense of the term, as the entities which are experienced in sensations proper; and so, too, are any patches of colour, or sounds, or smells, etc, (if such there be), which are not experienced at all.
In speaking of sensibles as _the sort of_ entities which are experienced in sensory experiences I seem to imply that all the entities which are experienced in sensory experiences have some common characteristic other than that which consists in their being so experienced. And I cannot help thinking that this is the case, in spite of the fact that it is difficult to see what intrinsic character can be shared in common by entities so different from one another as are patches of colour, sounds, smells, tastes, etc. For, so far as I can see, some non-sensory experiences may be exactly similar to sensory ones in all intrinsic respects, except that what is experienced in them is different in kind from what is experienced in any sensory experience: the relation meant by saying that in them something _is experienced_ may be exactly the same in kind, and so may the experient. And, if this be so, it seems to compel us to admit that the distinction between sensory and non-sensory experiences is derived from that between sensibles, and non-sensibles and not _vice versâ._ I am inclined, therefore, to think that all sensibles, in spite of the great differences between them, have some common intrinsic property, which we recognise, but which is unanalysable; and that, when we call an experience sensory, what we mean is not only that in it something is experienced in a particular way, but also that this something has this unanalysable property. If this be so, the ultimate definition of "sensibles" would be merely all entities which have this unanalysable property.
It seems to me that the term "sense-data" is often used, and may be correctly used, simply as a synonym for "sensibles"; and everybody, I think, would expect me, in discussing the status of sense-data, to discuss, among other things, the question whether there are any sensibles which are not "given." It is true that the etymology of the term "sense-data" suggests that nothing should be called a sense-datum, but what _is_ given; so that to talk of a non-given sense-datum would be a contradiction in terms. But, of course, etymology is no safe guide either as to the actual or the correct use of terms; and it seems to me that the term "sense-data" is often, and quite properly, used merely for _the sort of_ entities that are given in sense, and not in any way limited to those which are actually given. But though I think I might thus have used "sense-data" quite correctly instead of "sensibles," I think the latter term is perhaps more convenient; because though nobody ought to be misled by etymologies, so many people in fact are so. Moreover the term "sense-data" is sometimes limited in yet another way, viz, to the sort of sensibles which are experienced in _sensations proper_; so that in this sense "images" would not be "sense-data." For both these reasons, I think it is perhaps better to drop the term "sense-data" altogether, and to speak only of "sensibles."