Idea

[L:97] In the Logic, defined as "a concept of reason, whose object can be met with nowhere in experience", and thus cannot be known by us; Kant suggests, however, that such ideas "serve to guide the understanding through reason in respect of experience" by "using to their greatest perfection" the rules of reason. He associates such ideas with regulative principles, and gives as an example the idea of the universe, which is necessary "only as a regulative principle for the sake of the all-pervasive coherence of the empirical use of our understanding". [A320/B376] Similarly, in the Critique Kant speaks of the ideas of reason, which he also calls transcendental ideas, and he justifies abandoning (as hopelessly confused) the traditional meaning of the term. He writes, "a concept formed from notions [the source of pure concepts] and transcending the possibility of experience is an idea".

See Idea of the Good