Thus we may confidently say that however uncertain man's reactions upon his environment may sometimes seem in comparison with those of lower mammals, the uncertainty is probably not due to their possession of any principles of action which he lacks. _On the contrary, man possesses all the impulses that they have, and a great many more besides._ In other words, there is no material antagonism between instinct and reason. Reason, _per se_, can inhibit no impulses; the only thing that can neutralize an impulse is an impulse the other way. Reason may, however, make an _inference which will excite the imagination so as to let loose_ the impulse the other way; and thus, though the animal richest in reason is also the animal richest in instinctive impulses too, he never seems the fatal automaton which a _merely_ instinctive animal must be. =Two Principles of Non-uniformity.=--Instincts may be masked in the mature animal's life by two other causes. These are: _a._ The _inhibition of instincts by habits_; and _b._ The _transitoriness of instincts_. _a._ The law of =inhibition of instincts by habits= is this: _When objects of a certain class elicit from an animal a certain sort of reaction, it often happens that the animal becomes partial to the first specimen of the class on which it has reacted, and will not afterward react on any other specimen._ The selection of a particular hole to live in, of a particular mate, of a particular feeding-ground, a particular variety of diet, a particular anything, in short, out of a possible multitude, is a very wide-spread tendency among animals, even those low down in the scale. The limpet will return to the same sticking-place in its rock, and the lobster to its favorite nook on the sea-bottom. The rabbit will deposit its dung in the same corner; the bird makes its nest on the same bough. But each of these preferences carries with it an insensibility to _other_ opportunities and occasions--an insensibility which can only be described physiologically as an inhibition of new impulses by the habit of old ones already formed. The possession of homes and wives of our own makes us strangely insensible to the charms of those of other people. Few of us are adventurous in the matter of food; in fact, most of us think there is something disgusting in a bill of fare to which we are unused. Strangers, we are apt to think, cannot be worth knowing, especially if they come from distant cities, etc. The original impulse which got us homes, wives, dietaries, and friends at all, seems to exhaust itself in its first achievements and to leave no surplus energy for reacting on new cases. And so it comes about that, witnessing this torpor, an observer of mankind might say that no _instinctive_ propensity toward certain objects existed at all. It existed, but it existed _miscellaneously_, or as an instinct pure and simple, only before habit was formed. A habit, once grafted on an instinctive