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.