I do not wish, just now, to discuss the nature of attention; I wish only to point out that it enables us to take the first steps in abstraction. Out of the whole multiplicity of objects of sense, it enables us to single out a small selection, which is an indispensable preliminary to abstraction. For example, attention will enable us to discriminate a coloured pattern which we are seeing, and to separate it from the other things we see and from images and other objects of sense and thoughts which may exist simultaneously. For the sake of simplicity, let us suppose that we discriminate a black and white pattern in the form of a triangle. Within this pattern we can further discriminate sides and angles and an inside and outside--of course the sides are not mathematical lines nor the angles mathematical points. We now come to a question of very great importance, upon which our views of the relations of mind and matter largely depend. The question is this: What difference is there between the propositions “there is a triangle” and “I see a triangle”? Both these statements seem as certain as any statement can be--at least if rightly interpreted. As always happens in such cases, we are quite certain of something, but not quite certain what it is that we are certain of. I want to ask whether this something that we are certain of is really different in the above two statements, or whether the difference between them is only as to surroundings of which we are not certain. Most philosophers hold that there is a difference in what we are certain of; Mach, James, Dewey, the American realists, and I hold that the difference is in the uncertain context. Let us examine this question. The _suggestions_ of the two statements “I see a triangle” and “there is a triangle” are obviously different. The first states an event in my life, and suggests its possible effects upon me. The second aims at stating an event in the world, supposed to be equally discoverable by other people. You might say “there is a triangle” if you had seen it a moment ago but now had your eyes shut; in this case you would not say “I see a triangle”. On the other hand, one sometimes, under the influence of indigestion or fatigue, sees little black dots floating in the air; in such circumstances you would say “I see a black dot”, but not “there is a black dot”. This illustration shows that when you say “there is a black dot” you are making a stronger assertion than when you say “I see a black dot”. In the other case, when you say “there is a triangle” because you saw it a moment ago, though not now, you have three stages: First, memory assures you of the proposition “I saw a triangle”, and then you pass on to “there was a triangle”, and then, further, to “there is a triangle, because nothing can have happened to destroy it so quickly.” Here we have obviously passed far beyond the region of immediate certainty.