Thus, for these belated drinkers at the Kantian spring, we should have to admit consciousness as an 'epistemological' necessity, even if we had no direct evidence of its being there. But in addition to this, we are supposed by almost every one to have an immediate consciousness of consciousness itself. When the world of outer fact ceases to be materially present, and we merely recall it in memory, or fancy it, the consciousness is believed to stand out and to be felt as a kind of impalpable inner flowing, which, once known in this sort of experience, may equally be detected in presentations of the outer world. "The moment we try to fix our attention upon consciousness and to see _what_, distinctly, it is," says a recent writer, "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 know that there is something to look for."[6] "Consciousness" (Bewusstheit), says another philosopher, "is inexplicable and hardly describable, yet all conscious experiences have this in common that what we call their content has this peculiar reference to a centre for which 'self' is the name, in virtue of which reference alone the content is subjectively given, or appears ... While in this way consciousness, or reference to a self, is the only thing which distinguishes a conscious content from any sort of being that might be there with no one conscious of it, yet this only ground of the distinction defies all closer explanations. The existence of consciousness, although it is the fundamental fact of psychology, can indeed be laid down as certain, can be brought out by analysis, but can neither be defined nor deduced from anything but itself."[7] 'Can be brought out by analysis,' this author says. This supposes that the consciousness is one element, moment, factor--call it what you like--of an experience of essentially dualistic inner constitution, from which, if you abstract the content, the consciousness will remain revealed to its own eye. Experience, at this rate, would be much like a paint of which the world pictures were made. Paint has a dual constitution, involving, as it does, a menstruum[8] (oil, size or what not) and a mass of content in the form of pigment suspended therein. We can get the pure menstruum by letting the pigment settle, and the pure pigment by pouring off the size or oil. We operate here by physical subtraction; and the usual view is, that by mental subtraction we can separate the two factors of experience in an analogous way--not isolating them entirely, but distinguishing them enough to know that they are two. II