I have declared space and time to be part of the Principle of Individuation, as it is only space and time that make the multiplicity of similar objects a possibility. But multiplicity itself also admits of variety; multiplicity and diversity are not only quantitative, but also qualitative. How is it that there is such a thing as qualitative diversity, especially in ethical matters? Or have I fallen into an error the opposite of that in which Leibnitz fell with his identitas indiscernibilium?
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.
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 a 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 a 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 a priori element in all experience.
There are, then, three things that are a 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.