Part, therefore, of these objections to our theory may, I think, be met by admitting that _some_ of the ... sensible qualities which we perceive do not exist at the places where they appear to exist, though ethers do. But there is, I think, another class of cases, in which we may be justified in denying that two things which (it is asserted) cannot occupy the same space, really cannot. I will take an instance which is, I think, typical. When we look at a drop of blood with the naked eye, we perceive a small red spot, uniformly red all over. But when (as we say) we look at the _same_ object under a microscope of a certain power, I am informed that we see a much larger spot, of similar shape, indeed, but _not_ uniformly red--having, in fact, small red spots at different positions in a yellowish field. And if we were again to look at the _same_ object through a microscope of much higher power still, we might perceive yet a third different arrangement of colours. Is there any fatal objection to supposing that all _three_ appearances--the uniform red spot, the yellowish field with reddish spots in it, and the third, whatever that may be--do all really occupy the same real spatial area? I cannot see that there is. We are familiar with the idea that a given spatial area may contain parts which are invisible to us. And hence, I think it is quite conceivable that parts of a given area may be _really_ occupied by one colour, while the whole is _really_ occupied by another. And this, I think, is what we actually _do_ believe in many cases. At all events, we certainly believe that the area which appears to be occupied by one colour really is _the same area_ as that which appears to be occupied by another. And, unless we assume that the area, in both cases, really is the same, we can certainly have no reason to deny that each colour does really occupy the area which it appears to occupy.
For these reasons I think that the difficulties in the way of supposing that _some_ of the sensible qualities which we perceive as being in certain places, really exist in the places in which we perceive them to be, are not insuperable. I have indeed not done justice to these difficulties; but then, neither have I done justice to what is to be said on the other side. At all events, I think it is plain that we have no reason to assert, in any case whatever, that a perceived colour does _not_ really exist in the place where it is perceived as being, _unless_ we assume that that very same place really is occupied by something else_--either_ by some different sensible qualities _or_ by material objects such as physical science supposes to exist. But what reason can we give for such an assumption? I have tried to show that our own observations can give us none, _unless_ we assume that some of the sensible qualities, which we observe as occupying certain places, do really exist in those places. And, if this is so, then we must admit that neither he who believes (with Reid) in the existence of other minds and of matter also, nor he who believes in the existence of other minds and denies that of matter, can have, in his own observations, the slightest reason either for his assertion or for his denial: we must admit that he can have no reason for either assertion or denial, except one which consists in the assumption of the existence or nonexistence of something which he does _not_ observe--something, therefore, of the very same kind as that for which he gives it as a reason. I am very unwilling to suppose that this is the case: I am very unwilling to suppose that he who believes that Sindbad the Sailor really saw what the "Arabian Nights" represent him as seeing, has just as good reason (so far as his own observation goes) for believing this as he who denies it has for denying it. Still this may be the case. We _must_, perhaps, be content to assume as certain that for which our observation gives no reason: to assume such propositions as that Sindbad did _not_ see a Roc, and that you _do_ hear my voice. But if it is said that these things are certain; then it also appears to me to be certain that the colours which I perceive do exist (_some_ of them) where I perceive them. The more I look at objects round me, the more I am unable to resist the conviction that what I see does exist, as truly and as really, as my perception of it The conviction is overwhelming.
