The chief cause of intellectual diversity is to be found in the brain and nervous system. This is a fact which somewhat lessens the obscurity of the subject. With the brutes the intellect and the brain are strictly adapted to their aims and needs. With man alone there is now and then, by way of exception, a superfluity, which, if it is abundant, may yield genius. But ethical diversity, it seems, proceeds immediately from the will. Otherwise ethical character would not be above and beyond time, as it is only in the individual that intellect and will are united. The will is above and beyond time, and eternal; and character is innate; that is to say, it is sprung from the same eternity, and therefore it does not admit of any but a transcendental explanation. Perhaps some one will come after me who will throw light into this dark abyss. MORAL INSTINCT. An act done by instinct differs from every other kind of act in that an understanding of its object does not precede it but follows upon it. Instinct is therefore a rule of action given _à priori_. We may be unaware of the object to which it is directed, as no understanding of it is necessary to its attainment. On the other hand, if an act is done by an exercise of reason or intelligence, it proceeds according to a rule which the understanding has itself devised for the purpose of carrying out a preconceived aim. Hence it is that action according to rule may miss its aim, while instinct is infallible. On the _à priori_ character of instinct we may compare what Plato says in the _Philebus_. With Plato instinct is a reminiscence of something which a man has never actually experienced in his lifetime; in the same way as, in the _Phaedo_ and elsewhere, everything that a man learns is regarded as a reminiscence. He has no other word to express the _à priori_ element in all experience. There are, then, three things that are _à priori_: (1) Theoretical Reason, in other words, the conditions which make all experience possible. (2) Instinct, or the rule by which an object promoting the life of the senses may, though unknown, be attained. (3) The Moral Law, or the rule by which an action takes place without any object. Accordingly rational or intelligent action proceeds by a rule laid down in accordance with the object as it is understood. Instinctive action proceeds by a rule without an understanding of the object of it. Moral action proceeds by a rule without any object at all. _Theoretical Reason_ is the aggregate of rules in accordance with which all my knowledge--that is to say, the whole world of experience--necessarily proceeds. In the same manner _Instinct_ is the aggregate of rules in accordance with which all my action necessarily proceeds if it meets with no obstruction. Hence it seems to me that Instinct may most appropriately be called _practical reason_, for like theoretical reason it determines the _must_ of all experience.