Full Idea
Consistency is the highest obligation of a philosopher and yet the most rarely found.
Gist of Idea
Consistency is the highest obligation of a philosopher
Source
Immanuel Kant (Critique of Practical Reason [1788], I.1.1.§3)
Book Reference
Kant,Immanuel: 'Critique of Practical Reason (Third edition)', ed/tr. Beck,Lewis White [Library of Liberal Arts 1993], p.23
A Reaction
I agree with this, and it also strikes me as the single most important principle of Kant's philosophy, which is the key to his whole moral theory.