It is only necessary to analyse the judgement that men pass on the lawfulness of their actions, in order to find that, whatever inclination may say to the contrary, reason, incorruptible and self-constrained, always confronts the maxim of the will in any action with the pure will, that is, with itself, considering itself as a priori practical.
 Immanuel Kant, Critique of Practical Reason (1788). copy citation

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Author Immanuel Kant
Source Critique of Practical Reason
Topic judgement action
Date 1788
Language English
Reference
Note Translated by Thomas Kingsmill Abbott
Weblink http://www.gutenberg.org/cache/epub/5683/pg5683-images.html

Context

“{BOOK_1|CHAPTER_1 ^paragraph 75} Pure reason is practical of itself alone and gives (to man) a universal law which we call the moral law. REMARK. {BOOK_1|CHAPTER_1 ^paragraph 80} The fact just mentioned is undeniable. It is only necessary to analyse the judgement that men pass on the lawfulness of their actions, in order to find that, whatever inclination may say to the contrary, reason, incorruptible and self-constrained, always confronts the maxim of the will in any action with the pure will, that is, with itself, considering itself as a priori practical. Now this principle of morality, just on account of the universality of the legislation which makes it the formal supreme determining principle of the will, without regard to any subjective differences, is declared by the reason to be a law for all rational beings, in so far as they have a will, that is, a power to determine their causality by the conception of rules;” source