requires, although we are quite unable to determine the proper limits of this unity.
If the diversity existing in phenomena—a diversity not of form (for in this they may be similar) but of content—were so great that the subtlest human reason could never by comparison discover in them the least similarity (which is not impossible), in this case the logical law of genera would be without foundation, the conception of a genus, nay, all general conceptions would be impossible, and the faculty of the understanding, the exercise of which is restricted to the world of conceptions, could not exist. The logical principle of genera, accordingly, if it is to be applied to nature (by which I mean objects presented to our senses), presupposes a transcendental principle. In accordance with this principle, homogeneity is necessarily presupposed in the variety of phenomena (although we are unable to determine a priori the degree of this homogeneity), because without it no empirical conceptions, and consequently no experience, would be possible.
The logical principle of genera, which demands identity in phenomena, is balanced by another principle—that of species, which requires variety and diversity in things, notwithstanding their accordance in the same genus, and directs the understanding to attend to the one no less than to the other. This principle (of the faculty of distinction) acts as a check upon the reason and reason exhibits in this respect a double and conflicting interest—on the one hand, the interest in the extent (the interest of generality) in relation to genera; on the other, that of the content (the interest of individuality) in relation to the variety of species. In the former case, the understanding cogitates more under its conceptions, in the latter it cogitates more in them. This distinction manifests itself likewise in the habits of thought peculiar to natural philosophers, some of whom—the remarkably speculative heads—may be said to be hostile to heterogeneity in phenomena, and have their eyes always fixed on the unity of genera, while others—with a strong empirical tendency—aim unceasingly at the analysis of phenomena, and almost
