To say with Kant that the understanding is the principle of objectivity, that only through understanding is there for us an objective world, is sure to seem at first sight the extreme of perversity. We have come to think of the understanding as specially an agency of our own, and of the objective world as specially that which is presented to us independently of any such agency; as that which we find and do not make, and by which we have to correct the fictions of our own minds. When we ask, however, whether any impression is or represents anything real and objective, what exactly does the question mean, and how do we set about answering it? It is not equivalent to a question whether a feeling is felt. Some feeling must be felt in order to the possibility of the question being raised at all. It is a question whether a given feeling is what it is taken to be; or, in other words, whether it is related as it seems to be related. It may be objected indeed that, though some feeling or other must be felt in order to give any meaning to the question as to the objectivity of the impression or its correspondence with reality, yet still this question may and often does mean merely whether a particular feeling is felt. This is true; but a particular feeling is a feeling related in a certain way, and the question whether a particular feeling is really felt is always translatable into the form given—Is a feeling, which is undoubtedly felt, really related as some one thinking about it takes it to be? If an engine-driver, under certain conditions, permanent with him or temporary, sees a signal wrong, as we say, his disordered vision has its own reality just as much as if he saw right. There are relations between combinations of moving particles on the one side and his visual organs on the other, between the present state of the latter and certain determining conditions, between the immediate sensible effect and the secondary impressions which it in turn excites, as full and definite—with sufficient enquiry and opportunity, as ascertainable—as in any case of normal vision. There is as much reality in the one case as in the other, but it is not the same reality: i.e., it does not consist in the same relations. The engine-driver mistakes the effect of one set of relations for that of another, one reality for another, and hence his error in action. He may be quite innocent of a scientific theory of vision, but he objectifies his sensations. He interprets them as related in a certain way, and as always the same in the same relations; or, to use an equivalent but more familiar expressions, as signs of objects from which he distinguishes his feelings and by which he explains them. Were this not the case, his vision might be normal or abnormal, but he would be incapable of mistaking one kind of reality for another, since he would have no conception of reality at all. (§ 12 ¶ 1)