III. SENSIBILIA

I shall give the name sensibilia to those objects which have the same metaphysical and physical status as sense- data, without necessarily being data to any mind. Thus the relation of a sensibile to a sense-datum is like that of a man to a husband : a man becomes a husband by
SENSE-DATA AND PHYSICS 149
entering into the relation of marriage, and similarly a sensibile becomes a sense-datum by entering into the relation of acquaintance. It is important to have both terms ; for we wish to discuss whether an object which is at one time a sense-datum can still exist at a time when it is not a sense-datum. We cannot ask ' Can sense-data exist without being given ? " for that is like asking " Can husbands exist without being married ? ' We must ask " Can sensibilia exist without being given ? ' and also "Can a particular sensibile be at one time a sense-datum, and at another not ? ' Unless we have the word sensibile as well as the word "sense-datum," such questions are apt to entangle us in trivial logical puzzles.
It will be seen that all sense-data are sensibilia. It is a metaphysical question whether all sensibilia are sense- data, and an epistemological question whether there exist means of inferring sensibilia which are not data from those that are.
A few preliminary remarks, to be amplified as we pro- ceed, will serve to elucidate the use which I propose to make of sensibilia.
I regard sense-data as not mental, and as being, in fact, part of the actual subject-matter of physics. There are arguments, shortly to be examined, for their sub- jectivity, but these arguments seem to me only to prove physiological subjectivity, i.e. causal dependence on the sense-organs, nerves, and brain. The appearance which a thing presents to us is causally dependent upon these, in exactly the same way as it is dependent upon inter- vening fog or smoke or coloured glass. Both dependences are contained in the statement that the appearance which a piece of matter presents when viewed from a given place is a function not only of the piece of matter, but also of the intervening medium. (The terms used in
150 MYSTICISM AND LOGIC
this statement — " matter," " view from a given place," ' appearance," " intervening medium " — will all be de- fined in the course of the present paper.) We have not the means of ascertaining how things appear from places not surrounded by brain and nerves and sense-organs, because we cannot leave the body ; but continuity makes it not unreasonable to suppose that they present some appearance at such places. Any such appearance would be included among sensibilia. If — j>er impossibile — there were a complete human body with no mind in- side it, all those sensibilia would exist, in relation to that body, which would be sense-data if there were a mind in the body. What the mind adds to sensibilia, in fact, is merely awareness : everything else is physical or physio- logical.