Critique of Practical Reason: Philosophical Context for Critique of Practical Reason

Kant’s Influence on Philosophy

It is difficult to overestimate Kant's influence on philosophy. Even those who reject his explicit theories often use his terms, whether by wondering how it could be possible for something to be "synthetic" (not a matter of meaning) and yet "a priori" (knowable independent of experience), or by asking what is the source of an ethical "imperative." Kant has sometimes been credited for almost single-handedly creating the German philosophical tradition, and it certainly is hard to imagine what Hegel's or Marx's wrings would have looked like without the influence of Kant.

Many current day writers on philosophical ethics have been influenced by Kant. Some accept the categorical imperative as a valid test of moral rightness, but more commonly one will see Kant's linking of morality and autonomy, or his analysis of moral worth as an inner acceptance of the motive of duty, or his insistence that the good is what the moral aims at as opposed to morality being defined by its aim at the good.

The impact of Kant's writing style has arguably also been extensive, on which topic the twentieth century philosophy Walter Kaufmann tartly reports, "Few philosophers since Kant have approximated his genius, but many of his shortcomings are widely shared even today, and to some extant at least this is due to his phenomenal influence." Kant's insights are often masked by his convoluted sentences and unclear technical terms. Fortunately, the second Critique is significantly more accessible than the first, but still the second Critique elicits many conflicting interpretations.

The Critique of Practical Reason can be regarded as the sequel to the Critique of Pure Reason, picking up where that earlier book left off. In the first Critique, Kant divides our judgments in two ways—the a priori (knowable before experience) versus the a posteriori (knowable through experience) and the analytic (true by virtue of meaning) versus the synthetic (true by virtue of the facts). He ultimately concludes, first, that a posteriori judgments are about how things look to us, not about how things intrinsically are, since they are filtered through our experiences, and, second, all synthetic judgments are a posteriori, since we have no access to the world other than through experience.

This second conclusion rules out the possibility of metaphysically proving the existence of God, freedom, and immortality. It does leave open, though, the right to have faith that such things exist in the way the world is in itself, the noumenal realm, since we can never know what is true in that realm. The second Critique will take this further, arguing that the correct understanding of morality requires us to believe in God, freedom, and immortality. As well as continuing from the Critique of Pure Reason, the Critique of Practical Reason lays the grounds for the Metaphysics of Morals, written nine years later in 1797, and which applies the general moral principles of the second Critique to a variety of cases.

The second Critique in some senses can be seen as the opposite of the first Critique. While the main theme of the first Critique is how little we can know about its topic, metaphysics, the second Critique is about how we can know about its topic, morality. Not only that, but some of the first Critique is arguably taken back. We are directly aware of the application of the moral law to us, and through this, we are aware of our freedom, which, it turns out, is awareness of causation from the noumenal world. More than that, not only can we believe in God and immortality, as the first Critique agreed, but it turns out that reason commands belief in them.

In a different sense, though, the second Critique furthers the work of the first. Kant describes himself in the Critique of Pure Reason as having created a revolution to counter Copernicus’s revolution. Copernicus humbles man by removing him form the center of the physical universe, but Kant elevates him by presenting the whole phenomenal world of the senses as being created by us and by our senses. In the conclusion of the second Critique, Kant picks up this metaphor again, explaining how he has now shown how the human being lies at the center of the moral universe, and through that universe man connects with the noumenal world.