Through all this, the question becomes more and more pressing how certainty is to be attained, how judgements are to be established, in what knowledge and science consist; for, together with language and deliberate action, we extol these as the third great advantage conferred on us by the faculty of reason.
Reason is feminine in nature; it can give only after it has received. Of itself alone, it has nothing but the empty forms of its operation. There is absolutely no other perfectly pure rational knowledge than the four principles to which I have attributed metalogical truth, the principles of identity, of contradiction, of the excluded middle, and of sufficient reason of knowledge. For even the rest of logic is not perfectly pure rational knowledge, since it presupposes the relations and combinations of the spheres of concepts. But concepts in general exist only after previous representations of perception, and in the reference to these lies their whole nature; consequently, they presuppose these representations. As this assumption, however, does not extend to the definite content of concepts, but only to their general existence, logic can, on the whole, pass for a pure science of reason. In all the other sciences reason obtains its content from the representations of perception; in mathematics from the relations of space and time presented in intuition or perception prior to all experience; in pure natural science, that is to say, in what we know about the course of nature prior to all experience, the content of the science results from the pure understanding, i.e., from the a priori knowledge of the law of causality and of that law’s connexion with those pure intuitions or perceptions of space and time. In all the other sciences everything that is not borrowed from the sources just mentioned belongs to experience. To know means generally to have within the power of the mind, ready to reproduce at will, such judgements as have their sufficient ground of knowledge in something outside them, in other words, such judgements as are true. Thus only abstract knowledge is rational knowledge (Wissen), and this is therefore conditioned by the faculty of reason, and, strictly speaking, we cannot say of the animals that they rationally know anything, although they have knowledge of perception, as well as recollection of it, and, on this very account, imagination; this, moreover, is proved by their dreaming. We attribute to them consciousness, and although the name (Bewusstsein) is derived from wissen (to know rationally), the concept of consciousness coincides with that of representation in general, of whatever kind it may be. Thus to the plant we attribute life, but not consciousness. Rational knowledge (Wissen) is therefore abstract consciousness, fixing in concepts of reason what is known generally in another way.