Critique of Practical Reason

Overview

The Critique of Practical Reason is a hundred and eighty pages, published in 1788, three years after the Groundwork and seven after the first Critique. It is shorter than either and it is not the place to start with Kant’s ethics.

The order to read them in is Groundwork first, then this. The Groundwork is a hundred pages, it introduces the categorical imperative and its formulations, and it is where the famous examples live. This book assumes all of that and does something different: it asks what the moral law shows about the kind of beings we are, and it fits ethics into the architecture of the critical philosophy.

The structure mirrors the first Critique, which is deliberate and slightly confusing. There is an Analytic and a Dialectic, and the parts do not correspond to what those words meant in the earlier book. In the first Critique the Analytic showed what we can know and the Dialectic showed what happens when reason overreaches. Here the Analytic establishes the moral law and the Dialectic resolves an antinomy about the highest good.

The prose is Kant’s usual: long sentences, technical vocabulary used with total consistency, and no concessions. Gregor’s translation in the Cambridge edition is the standard and gives the German pagination in the margins, which is how Kant is cited.

The argument

That pure reason can be practical. The question the book exists to answer. Empiricists held that reason can tell you how to get what you want and that wanting comes from elsewhere; Hume had put it most sharply, making reason the servant of the passions and nothing else. Kant’s claim is the opposite: reason on its own can determine the will, without borrowing any motive from desire, and morality is what that looks like.

He argues it by distinguishing two kinds of practical principle. Maxims are subjective and hold for the person who adopts them. Laws are objective and hold for every rational being. Any principle whose motive is the satisfaction of a desire belongs to what Kant calls the lower faculty of desire and cannot be a law, because what satisfies me need not satisfy you and nothing about it is necessary. A law must therefore determine the will by its form alone, which is to say by its universality, and that gives the fundamental law: act so that the maxim of your will could hold at the same time as the principle of a universal legislation.

The fact of reason. Here Kant does something he had not done in the Groundwork and that has troubled readers since. He does not argue that we are under the moral law. He says we are conscious of it, immediately, as a fact of reason, in the same way we are conscious of the forms of intuition. The example he gives is a man told he will be executed unless he gives false testimony that will destroy an innocent person: he may not be certain he would refuse, but he knows without hesitation that he could, and that knowledge of what he could do reveals a freedom he would otherwise never have suspected.

The order of discovery matters and Kant is explicit about it. Freedom is the condition of the moral law, but the moral law is what makes us aware of freedom. We do not prove we are free and then conclude we are obliged; we find ourselves obliged and conclude that we must be free.

Freedom and the first Critique. This is where the two books lock together. The first Critique had shown that everything in the world of appearances is causally determined, and that reason cannot decide whether freedom is possible, only that the question is undecidable from the theoretical side. Kant now says that this limitation was not a loss but a clearing: because we cannot know that we are determined at the level of things in themselves, there is room for freedom there, and the moral law tells us to occupy it. He had written in the first Critique’s preface that he had to deny knowledge in order to make room for faith, and this is what he meant.

Respect. A short chapter on the only feeling Kant lets into the system. The moral law strikes down self-conceit and humiliates our self-love, and the effect of that humiliation is respect, which is not a motive we happen to have but something the law produces in any being like us. It is negative in origin and positive in effect, and Kant’s treatment of it is more psychologically acute than his reputation suggests.

The Dialectic and the postulates. The last part, and the most contested. Kant defines the highest good as virtue together with the happiness proportioned to it, and points out an apparent contradiction: virtue does not produce happiness in this world, and pursuing happiness does not make anyone virtuous, yet reason demands that the two belong together.

His resolution is the doctrine of the postulates. Practical reason is entitled to assume three things it cannot know. Freedom, already established. Immortality, because the moral law demands a holiness of will that no finite being achieves in a lifetime, so an endless progress must be possible. And God, because only a being that is both author of nature and moral legislator could bring it about that virtue and happiness coincide.

Kant is careful about the status of these. They are not theoretical knowledge, they extend no understanding, and they are not arguments for the existence of anything. They are assumptions we are rationally permitted, and required, to make in order that the moral enterprise not be incoherent.

The conclusion. Two pages, and the most famous passage he wrote. Two things fill the mind with admiration and awe: the starry heavens above and the moral law within. The first shows him a body in a vast universe, annihilating his importance as a speck of matter that must give back to the planet the matter it was made of. The second raises his worth infinitely, revealing a life independent of the whole sensible world. It is on his tombstone in Kaliningrad.

How to read it

Read the Groundwork first. This book will be largely opaque without it.

Read the Analytic entire, particularly the sections on the fact of reason and the chapter on respect, and then the Conclusion.

Take the Dialectic and the postulates slowly and decide what you make of them. Many readers, including admirers of Kant’s ethics, take the postulates to be a retreat: a philosopher who has just built a morality that needs no God bringing him back to make the accounts balance. Others argue the move is exactly right, that a demand which could never be satisfied would be irrational, and that Kant is being honest about what his ethics presupposes.

Watch the distinction between acting from duty and acting in accordance with it. This is what people attack Kant for, usually by way of Schiller’s joke about the man who is troubled because he enjoys helping his friends and therefore suspects he is not being moral. Kant’s point is narrower than the caricature: he is asking what demonstrates a good will, not what makes an action decent.

Read it against Mill’s Utilitarianism. They are the two poles of modern moral philosophy, one locating rightness in the form of the willing and one in the consequences, and neither has absorbed the other in two centuries.

Questions it raises

• Is the moral law a fact of reason, or has Kant assumed what he needed to prove?
• Ought implies can, so we are free. How much weight can that inference bear?
• The postulates are permitted rather than proved. Is a belief one is rationally entitled to hold, without evidence, a belief at all?
• Acting from duty is distinguished from acting in accordance with it. Does that make the person who enjoys being kind less admirable, and did Kant mean it to?
• The highest good requires that virtue and happiness coincide. Why should reason demand that, rather than accepting that they do not?
• The first Critique limited knowledge to make room for faith. Is that a discovery about the limits of reason, or a philosophy built to arrive where its author wanted?