Ernst Heinrich Haeckel, the French idealist philosopher, carried further the neocriticism of Charles Renouvier and Jules Lachelier. Renouvier had criticized the categories of Immanuel Kant, maintaining that the category of relation really included all the others. He had also criticized the fact that Kant had not included personality in the categories, though he should have, since the will determines thought no less than does speculative reason. Thought, according to Renouvier, manifests relation in two ways—in the relations of its elements to each other, and in the relation of judgment to consciousness. The latter relation is always unique because consciousness displays its spontaneity in the synthesis of the objects which it posits.

Hamelin started from a similar position; in fact, he always declared himself a disciple of Renouvier. However, Renouvier had taken account of contingency and discontinuity, and for him the pursuit of truth...