Groundwork of the Metaphysics of Morals | Study Guide

Immanuel Kant

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Groundwork of the Metaphysics of Morals | Section 3 : Transition from Metaphysics of Morals to the Critique of Pure Practical Reason | Summary



So far, Kant has identified an a priori moral law binding on all rational beings. Such a law presupposes that these beings are free. Were they not free but still purely rational, they could not do otherwise than what reason dictates. In that case there would be no need for any sort of law. Kant has yet to establish that there is human freedom—that, as the source of the moral law, human beings are their own causality, rather than subject to an external causality.

Events in the natural world are determined by antecedent conditions: every event is caused. A dropped pen falls to the floor, for example. Morality, on the other hand, presupposes the freedom to act or not to act in a certain way. Moreover, it presupposes that an action is a sort of cause that is itself not determined by antecedent conditions. That cause has a law (moral) that explains the action, just as the cause of the pen dropping has a law (physical) that explains its action. In the latter case the cause is autonomous. In the former no such cause is possible—pens are mere bodies. A free will cannot be caused, then, but is itself a cause. Moreover, awareness of moral demands is a presupposition of freedom—it is the a priori idea that the will is free to be obligated in this way. So, although there is no rational proof of the freedom required for morality, there is room to think that the causal network of the physical world applies also to the moral agent.


Kant recognizes that human beings are not purely rational but also empirical beings. As such, humans are subject to physical laws—unable, for example, to ignore gravity. In the physical world all events are caused, which means all events are determined by antecedent conditions. How is it possible, then, for one to be motivated by reason's commands? How is it possible for choice and deliberation to occur when all natural events are caused? These are the main questions Kant answers in this final section of Groundwork. If humans are free, and if reason can motivate moral action, then the categorical imperative is binding. The challenge Kant has in Section 3 is to show that it is plausible to think both that humans are free and that reason can motivate moral action, despite the fact that natural, or causal, determinism exists in the empirical world.

Kant thinks it is impossible to prove that humans have free will. However, he argues that it is at least not inconceivable that they do. Indeed, when one deliberates about what to do, and when one chooses what to do, one presupposes that one is free. Not only this, but one also presupposes that one can be motivated by reason. Here again, while Kant thinks people do make such a presupposition, he does not think it can be proven that reason does so motivate. He simply believes it is advisable that we act as if it does, because otherwise we have no basis for morality.

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