Its aim is to approximate the rule to universality, i.e. to bring systematic unity, so far as possible, into the body of our detailed knowledge. This unity is the criterion of the truth of its rules. The systematic unity is only a projected unity. The systematic unity is a logical principle To secure an empirical criterion, we must presuppose the systematic unity of nature as objectively valid and necessary. Aims at the unity of knowledge.
Reason demands that no genera be the highest.
The law of reason which requires us to seek for systematic unity is a necessary law, since without it we should have no reason at all, and without reason no coherent employment of the understanding, and in the absence of this, no sufficient criterion of empirical truth. In other words we must assume our rules conform to nature. If the appearances which present themselves were of so great a variety that understanding could never by comparison detect the slightest similarity, we would not have any universal concept and the understanding itself would not exist. The logical principle of genera is balanced by the Principle of Species which prescribes to the understanding that it attend to diversity no less than to identity. Aims at the systematic completeness of knowledge.