The Metaphysics of Morals by Immanuel Kant Chapter 1 Page 27

every impulse which could arise to it from obedience to any law, there remains nothing but the universal conformity of its actions to law in general, which alone is to serve the will as a principle, i.e., I am never to act otherwise than so that I could also will that my maxim should become a universal law. Here, now, it is the simple conformity to law in general, without assuming any particular law applicable to certain actions, that serves the will as its principle and must so serve it, if duty is not to be a vain delusion and a chimerical notion.

The common reason of men in its practical judgements perfectly coincides with this and always has in view the principle here suggested. Let the question be, for example: May I when in distress make a promise with the intention not to keep it? I readily distinguish here between