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 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 proceed, 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 subjectivity, 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 intervening 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 this statement--"matter," "view from a given place," "appearance," "intervening medium"--will all be defined 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--_per impossibile_--there were a complete human body with no mind inside 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 physiological. IV. SENSE-DATA ARE PHYSICAL