also exist. The content of the thing is what we assert to exist, when we assert that the thing exists.
When, therefore, blue is said to be part of the content of the "sensation of blue," the latter is treated as if it were a whole constituted in exactly the same way as any other "thing." The "sensation of blue," on this view, differs from a blue bead or a blue beard, in exactly the same way in which the two latter differ from one another: the blue bead differs from the blue beard, in that while the former contains glass, the latter contains hair; and the "sensation of blue" differs from both in that, instead of glass or hair, it contains consciousness. The relation of the blue to the consciousness is conceived to be exactly the same as that of the blue to the glass or hair: it is in all three cases the quality of a thing.
But I said just now that the sensation of blue was analysed into "content" and "existence," and that blue was said to be the content of the idea of blue. There is an ambiguity in this and a possible error, which I must note in passing. The term "content" may be used in two senses. If we use "content" as equivalent to what Mr. Bradley calls the "what"—if we mean by it the whole of what is said to exist, when the thing is said to exist, then blue is certainly not the content of the sensation of blue: part of the content of the sensation is, in this sense of the term, that other element which I have called consciousness. The analysis of this sensation into the "content" "blue," on the one hand, and mere existence on the other, is therefore certainly false; in it we have again the self-contradictory identification of "Blue exists" with "The sensation of blue exists," But there is another sense in which "blue" might properly be said to be the content of the sensation—namely, the sense in which "content," like εἴδος is opposed to "substance" or "matter." For the element "consciousness," being common to all sensations, may be and certainly is regarded as in some sense their "substance," and by the "content" of each is only meant that in respect of which one differs from another. In this sense then "blue" might be said to be the content of the sensation; but, in that case, the analysis into "content" and "existence" is, at least, misleading, since under "existence" must be included "what exists" in the sensation other than blue.
We have it, then, as a universally received opinion that blue is related to the sensation or idea of blue, as its content, and that this view, if it is to be true, must mean that blue is part of what is said to exist when we say that the sensation exists. To say that the sensation exists is to say both that blue exists and that "consciousness," whether we call it the substance of which blue is the content or call it another part of the content, exists too. Any sensation or idea is a "thing," and what I have called its object is the quality of this thing. Such a "thing" is what we think of when we think of a mental image. A mental image is conceived as if it were related to that of which it is the image (if there be any such thing) in exactly the same way as the image in a looking-glass is related to that of which it is the reflection; in both cases there is identity of content, and the image in the looking-glass differs from that in the mind solely in respect of the fact that in the one case the other constituent of the image is "glass" and in the other case it is consciousness. If the image is of blue, it is not conceived that this "content" has any relation to the consciousness but what it has to the glass: it Is conceived merely to be its content. And owing to the fact that sensations and ideas are all considered to be wholes of this description—things in the mind—the question: What do we know? is considered to be identical with the question: What reason have we for supposing that there are things outside the mind corresponding to these that are inside it?
What I wish to point out is (1) that we have no reason for supposing that there are such things as mental images at all—for supposing that blue is part of the content of the sensation of blue, and (2) that even if there are mental images, no mental image and no sensation or idea is merely a thing of this kind: that 'blue,' even if it is part of the content of the image or sensation or idea of blue, is always also related to it in quite another way, and that this other relation, omitted in the traditional analysis, is the only one which makes the sensation of blue a mental fact at all.
The true analysis of a sensation or idea is as follows. The element that is common to them all, and which I have called "consciousness," really is consciousness. A sensation is, in reality, a case of 'knowing' or 'being aware of' or 'experiencing' something. When we know that the sensation of blue exists, the fact we know is that there exists an awareness of blue. And this awareness is not merely, as we have hitherto seen it must be, itself something distinct and unique, utterly different from blue: it also has a perfectly distinct and unique relation to blue, a relation which is not that of thing or substance to content, nor of one part of content to another part of content. This relation is just that which we mean in every case by 'knowing.' To have in your mind 'knowledge' of blue, is not to have in your mind a 'thing' or 'image' of which blue is the content. To be aware of the sensation of blue is not to be aware of a mental image—of a "thing," of which 'blue' and some other element are constituent parts in the same sense in which blue and glass are constituents of a blue bead. It is to be aware of an awareness of blue; awareness being used, in both cases, in exactly the same sense. This element, we have seen, is certainly neglected by the 'content' theory: that theory entirely fails to express the fact that there is, in the sensation of blue, this unique relation between blue and the other constituent. And what I contend is that this omission is not mere negligence of expression, but is due to the fact that though philosophers have recognised that something distinct is meant by consciousness, they have never yet had a clear conception of what that something is. They have not been able to hold it and blue before their minds and to compare them, in the same way in which they can compare blue and green. And this for the reason I gave above: namely that the moment we try to fix our attention upon consciousness and to see what, distinctly, it is, it seems to vanish: it seems as if we had before us a mere emptiness. When we try to introspect the sensation of blue, all we can see is the blue: the other element is as if it were diaphanous. Yet it can be distinguished if we look attentively enough, and if we know that there is something to look for. My main object in this paragraph has been to try to make the reader see it; but I fear I shall have succeeded very ill.
It being the case, then, that the sensation of blue includes in its analysis, beside blue, both a unique element 'awareness' and a unique relation of this element to blue, I can make plain what I meant by asserting, as two distinct propositions, (1) that blue is probably not part of the content of the sensation at all, and (2) that, even it were, the sensation would nevertheless not be the sensation of blue, if blue had only this relation to it. The first hypothesis may now be expressed by saying that, if it were true, then, when the sensation of blue exists, there exists a blue awareness: offence may be taken at the expression, but yet it expresses just what should be and is meant by saying that blue is, in this case, a content of consciousness or experience. Whether or not, when I have the sensation of blue, my consciousness or awareness is thus blue, my introspection does not enable me to decide with certainty: I only see no reason for thinking that it is. But whether it is or not, the point is unimportant, for introspection does enable me to decide that something else is also true: namely that I am aware of blue, and by this I mean, that my awareness has to blue a quite different and distinct relation. It is possible, I admit, that my awareness is blue as well as being of blue: but what I am quite sure of is that it is of blue; that it has to blue the simple and unique relation the existence of which alone justifies us in distinguishing knowledge of a thing from the thing known, indeed in distinguishing mind from matter. And this result I may express by saying that what is called the content of a sensation is in very truth what I originally called it—the sensation's object.
But, if all this be true, what follows?
Idealists admit that some things really exist of which they are not aware: there are some things, they hold, which are not inseparable aspects of their experience, even if they be inseparable aspects of some experience. They further hold that some of the things of which they are sometimes aware do really exist, even when they are not aware of them: they hold for instance that they are sometimes aware of other minds, which continue to exist even when they are not aware