should reach independence, might be extended indefinitely. Here again, then, the greatest success was achieved on the side of the greatest risk. _Instinct and intelligence therefore represent two divergent solutions, equally fitting, of one and the same problem._ There ensue, it is true, profound differences of internal structure between instinct and intelligence. We shall dwell only on those that concern our present study. Let us say, then, that instinct and intelligence imply two radically different kinds of knowledge. But some explanations are first of all necessary on the subject of consciousness in general. It has been asked how far instinct is conscious. Our reply is that there are a vast number of differences and degrees, that instinct is more or less conscious in certain cases, unconscious in others. The plant, as we shall see, has instincts; it is not likely that these are accompanied by feeling. Even in the animal there is hardly any complex instinct that is not unconscious in some part at least of its exercise. But here we must point out a difference, not often noticed, between two kinds of unconsciousness, viz., that in which consciousness is _absent_, and that in which consciousness is _nullified_. Both are equal to zero, but in one case the zero expresses the fact that there is nothing, in the other that we have two equal quantities of opposite sign which compensate and neutralize each other. The unconsciousness of a falling stone is of the former kind: the stone has no feeling of its fall. Is it the same with the unconsciousness of instinct, in the extreme cases in which instinct is unconscious? When we mechanically perform an habitual action, when the somnambulist automatically acts his dream, unconsciousness may be absolute; but this is merely due to the fact that the representation of the act is held in check by the performance of the act itself, which resembles the idea so perfectly, and fits it so exactly, that consciousness is unable to find room between them. _Representation is stopped up by action._ The proof of this is, that if the accomplishment of the act is arrested or thwarted by an obstacle, consciousness may reappear. It was there, but neutralized by the action which fulfilled and thereby filled the representation. The obstacle creates nothing positive; it simply makes a void, removes a stopper. This inadequacy of act to representation is precisely what we here call consciousness.