The theory, therefore, that nothing exists, except when it is perceived, is no objection (even if it be true) to the supposition that colours do exist. What objections are there to this supposition? All serious objections to it are, I think, of one type. They all rest upon the assumption that, if a certain kind of thing exists at a certain time in a certain place, certain other kinds of things cannot exist at the same time in the same place. They are all, that is to say, of the same type as Berkeley's argument: that, though the same body of water may _appear_ to be simultaneously both hot and cold (if one of the hands we plunge into it is warm and the other cold), yet the heat and the cold cannot both _really_ be in the same body at the same time. And it is worth noticing that anyone who uses this argument must admit that he understands what is meant by "really existing in a given place," and that he means by it something _other_ than "being perceived as in a given place." For the argument itself admits that _both_ the heat _and_ the cold _are_ really _perceived_ as being in the same place, and that there is no difficulty in supposing that they are so; whereas It urges that there _is_ a difficulty in supposing that they both _really exist_ in it.
Now there is one obvious defect in this type of argument, if designed to prove that _no_ sensible quality exists at any place where it is perceived as being--a defect, which Berkeley himself admits in his "Principles," though he omits to notice it where he repeats the argument in his "Hylas." Even if we assume that the heat and the cold cannot _both_ exist in the same place (and I admit that, in this case, the contrary assumption does seem repugnant to Common Sense), it does not follow that _neither_ exists there. That is to say this type of argument, even if we grant its initial assumption, will only entitle us to conclude that _some_ sensible qualities which we perceive as being in a certain place at a certain time, do not exist in that place at that time. And this conclusion, I am inclined to think, is true. In the case, for instance, of the so-called "images" which we perceive in a looking-glass, we may very readily admit that the colours and shapes which we perceive do _not_ exist at the places where they appear to be--namely at various distances behind the glass. But yet, so far as I can see, we have no reason whatever for supposing that they do not, _except_ the assumption that our observations give us reason to believe that _other_ sensible qualities _do_ exist in those positions behind the glass; and the assumption that _where_ these _other_ sensible qualities do exist, those which we see in the glass do _not_ exist. I should, therefore, admit that _some_ sensible qualities which we perceive as being in certain places, do _not_ exist in those places, while still retaining my belief that others do. And _perhaps_ this explanation is the one which should also be adopted in the case of sensible qualities which appear to be at a great distance from us. When, for instance, (as we say), "we see the moon," _what_ we perceive (if the moon be full) is a round bright silver disc, of a small size, at a place very distant from us. Does that silver disc exist at that place? With what suppositions does the assumption that it _does_ conflict? Only, so far as I can see, with the supposition that the place in question is _really_ occupied by a body such as science has taught us to suppose that the moon _really_ is--a spherical body immensely larger than objects, in comparison with which the silver disc which we perceive is small; _or else_ with the supposition that the place in question is really occupied by some part of our atmosphere, or some part of the medium which science supposes to exist between our atmosphere and the moon; _or else_ with the supposition that the place in question is really occupied by what we might see, if the moon were nearer to us by many thousands of miles. Unless we suppose that some other object _is_ in the place, in which the silver disc appears to be, and that this object is of a kind which cannot occupy the _same_ place which is occupied by a silver disc, we have no reason to suppose that the silver disc does _not_ really exist in the place where it appears to be. And, in this case, we _perhaps_ have reason for both suppositions and should therefore conclude that the silver disc, which we perceive, does not exist in any real place.