There, too often, the matter is left, B feeling that A is profoundly unclear about what he is asking for, and A reckoning that B’s refusal to have his difficulty indicates only a lack of depth and a narrowness of technique. A’s position is quite shocking, despite the fact that many discussions (both inside and outside philosophy) often come perilously close to it. Because if you and I can never know whether we are having the same experience in those situations where we both confront, e.g. a stoplight, and respond by saying “Red,” then we can certainly never know whether we are having the same experience when we are looking at triangles, or chairs, or tables, or other people, or any of the other philosophical furniture of the external world. To have the doubt which A expresses just is to entertain the most radical kind of solipsism, although many seem to have had the former without explicitly entertaining the latter. It is hardly satisfactory to point out here, as some recent philosophers, like B above, seem to have thought it sufficient to do, that the question is not a soluble one. This is precisely what A is claiming. Discussions often conclude therefore in agreeing that the difficulty is insoluble and then proceed to construct theories as to how it is that A and B ever manage to agree upon so much in the world, despite their disagreements about “basic” visual experience. Here words like “convention”, “agreement”, “stipulation”, and “ostensive”, are exercised rather heavily. We can, apparently, never really know that we have the same “inner” visual experiences. But we can, by various sorts of arbitrary agreements and conventional decisions, proceed to act as if we do have the same experiences. The value of the agreements and decisions is assessed pragmatically. If we can all succeed in managing our affairs in the world by agreeing that X and deciding that Y, then in so far do we rely on X and Y.