/ Dictionary / Index I idea of pure reason: Meaning and Definition of Find definitions for: ide'a of pure' rea'son Pronunciation: [key] — Kantianism. Kantianism. any of the three undemonstrable entities (a personal soul, a cosmos, and a supreme being) implicit in the fact of a subject and an object of knowledge, and in the need for some principle uniting them. Cf. ideal of pure reason. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. ideamonger ideate Related Content Daily Word Quiz: fabricate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language