For men and all created rational beings moral necessity is constraint, that is obligation, and every action based on it is to be conceived as a duty, not as a proceeding previously pleasing, or likely to be pleasing to us of our own accord.
 Immanuel Kant, Critique of Practical Reason (1788). copy citation

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

Context

“It is of the greatest importance to attend with the utmost exactness in all moral judgements to the subjective principle of all maxims, that all the morality of actions may be placed in the necessity of acting from duty and from respect for the law, not from love and inclination for that which the actions are to produce. For men and all created rational beings moral necessity is constraint, that is obligation, and every action based on it is to be conceived as a duty, not as a proceeding previously pleasing, or likely to be pleasing to us of our own accord. As if indeed we could ever bring it about that without respect for the law, which implies fear, or at least apprehension of transgression, we of ourselves, like the independent Deity, could ever come into possession of holiness of will by the coincidence of our will with the pure moral law becoming as it were part of our nature, never to be shaken” source