Critique of Practical Reason

“Nothing worse could happen to these labors than that someone should make the unexpected discovery that there is and can be no a priori cognition at all. But there is no danger of this. It would be tantamount to someone’s wanting to prove by reason that there is no reason.”

A key part of Kant’s philosophy is that he believes there are certain fundamental principles that are self-evident. Along with the existence of freedom or free will (3), another of these is that there is such a thing as a priori reasoning or reasoning through intuition.

“Now there enters here a concept of causality justified by the Critique of Pure Reason although not capable of being presented empirically, namely that of freedom; and if we can now discover grounds for proving that this property does in fact belong to the human will (and so to the will of all rational beings as well), then it will not only be shown that pure reason can be practical but that it alone, and not reason empirically limited, is unconditionally practical.”

The existence of free will, which Kant takes as a postulate—or a self-evident truth—is in many ways the touchstone of Kant’s philosophy as expressed in Critique of Practical Reason. For Kant, free will is also evidence of causality and of practical reason itself.

“Now tell someone that he ought never to make a lying promise; this is a rule that has to do only with his will, regardless of whether the purposes the human being may have can be thereby attained; the mere volition is that which is to be determined completely a priori by this rule.”

This is an example of a moral law, which is both conditional and universal. Through a priori reasoning, Kant believes such a law cannot be determined by subjective situations or conditions.

“The matter of a practical principle is the object of the will.”

Although every human being possesses a free will, Kant also believes that all free wills strive toward certain goals or objects. Fulfillment of the moral law is one of these. What is subjective is whether and how individual will decides to follow the moral law.

“We can become aware of pure practical laws just as we are aware of pure theoretical principles, by attending to the necessity with which reason prescribes them to us and to the setting aside of all empirical conditions to which reason directs us.”

In this passage, Kant means that we can determine a moral law by both our feeling of duty to fulfill the law (29) and if by using reason to figure out whether we are compelled to follow the law simply because of subjective desires and influences.

“The maxim of self-love (prudence) merely advises; the law morality commands.”

In Kant’s view, this is the fundamental reason why happiness cannot be said to be a universal law and a core difference between subjective emotion and moral law. Emotions including self-love or happiness are only subjective and conditional. The moral law is objective and unconditional.

“As for my labor in the Critique of Pure Reason, which was occasioned by that Humean skeptical teaching but went much further and included the whole field of pure theoretical reason in its synthetic use and so too the field of what is generally called metaphysics, I proceeded as follows with respect to the doubt of the Scottish philosopher concerning the concept of causality.”

Here, Kant hints at how shaken he was by the radically empirical philosophy of David Hume. Particularly, Hume’s questioning of common assumptions regarding cause and effect forced Kant to reevaluate his own philosophical assumptions about God.

“This is the place to explain the paradox of method in a Critique of Practical Reason, namely, that the concept of good and evil must not be determined before the moral law (for which, as it would seem, this concept would have to be made the basis) but only (as was done here) after it and by means of it.”

Kant considers practical reason necessary for deciding questions of good and evil, as such questions are not always straightforward. Kant gives the example of a surgery that may be regarded as “evil” in the pain it will cause the patient but will ultimately be “good” in that it will restore the patient’s health (51-52).

“The rule of judgment under laws of pure practical reason is this: ask yourself whether, if the action you propose were to take place by a law of the nature of which you were yourself a part, you could indeed regard it as possible through your will. Everyone does, in fact, appraise actions as morally good or evil by this rule.”

This is an explanation of how practical reason works in practice. We determine what is subjective (whether a situation is good or evil) in accordance with standards that, at least in Kant’s view, are universal and objective.

“What is essential in every determination of the will by the moral law is that, as a free will—and so not only without the cooperation of sensible impulses but even with rejection of all of them and with infringement upon all inclinations insofar as they could be opposed to that law—it is determined solely by the law.”

One of Kant’s overriding aims, although he does not explicitly state it, is to refute the popular Enlightenment belief that emotions and emotional bonds formed the basis of morality. Instead, he asserts here and elsewhere in Critique of Practical Reason that emotions, because they are always subjective and conditional, cannot form a foundation for morality, which instead exists through universal and objective laws.

“In the whole of creation everything one wants and over which one has any power can also be used merely as a means; a human being alone, and with him every rational creature, is an end in itself: by virtue of the autonomy of his freedom he is the subject of the moral law, which is holy.”

One might see Kant’s universal and objective moral law as proof against the idea of human free will. However, for Kant, the two ideas are intertwined. If free will did not exist, morality would be meaningless—a “puppet show” (118), as he calls it in Book 2.

“Thus the question, how is the highest good practically possible? still remains an unsolved problem despite all the attempts at coalition that have hitherto been made.”

The paradox behind the highest good is that we can conceptualize it and strive to follow it, yet it is impossible for human beings to attain it because we are mortal and have limited abilities and perspectives. Still, for Kant, this contradiction is evidence for the existence of the highest good, as well as of the existence of God and the immortality of the human soul.

“Freedom, and the consciousness of freedom as an ability to follow the moral law with an unyielding disposition, is independence from the inclinations, at least as motives determining (even if not as affecting) our desire.”

Further proof of the existence of the moral law is that we do not follow our subjective, empirically grounded emotions. Instead, humans are often motivated to follow higher moral directives, even at the expense of our own self-interest and happiness.

“Therefore the supreme cause of nature, insofar as it must be presupposed for the highest good, is a being that is the cause of nature by understanding and will (hence its author), that is, God.”

Kant’s argument for the existence of God is complex (100-101). However, essentially his argument refers back to the highest good, which Kant considers the perfect attainment of both happiness and virtue. The very fact that people can imagine and we strive toward an unattainable moral ideal is a rational argument for the existence of God.

“For this reason, again, morals is not properly the doctrine of how we are to make ourselves happy but of how we are to become worthy of happiness.”

There is a distinction in Kant’s philosophy between happiness achieved by the fulfillment of conditional desires and happiness achieved through becoming worthy of happiness by means of virtue. The latter is practically impossible to achieve within one’s mortal lifetime, yet it is what Kant considers true happiness and part of the highest good (90).

“Once this is done, reality is given to the concept of the object of a morally determined will (that of the highest good) and with it to the conditions of its possibility, the ideas of God, freedom, and immortality, but always only with reference to the practice of the moral law (not for any speculative purpose).”

One can see Kant’s main thesis in Critique of Practical Reason as a collection of concepts that support and reinforce each other. These concepts are moral laws, the three postulates (free will, God, and the immortality of the soul), and the greatest good.

“On the other hand, a need of pure practical reason is based on a duty, that of making something (the highest good) the object of my will so as to promote it with all my powers.”

The way the moral law operates, according to Kant, is through a feeling of duty and respect for the moral law itself. Unlike empirical emotions such as happiness, this feeling of duty is neither a feeling of pleasure nor of displeasure (22).

“I will that there be a God, that my existence in this world be also an existence in a pure world of the understanding beyond natural connections, and finally that my duration be endless; I stand by this, without paying attention to rationalizations, however little I may be able to answer them or to oppose them with others more plausible, and I will not let this belief be taken from me; for this is the only case in which my interest, because I may not give up anything of it, unavoidably determines my judgment.”

Free will is the basis for not only Kant’s belief in God, but also his belief that, as a human being, he exists in realms of both material reality and abstract thought. In this passage, he again asserts his opposition to the “abyss of skepticism” (3) he attributes to Hume’s philosophy.

“As long as human nature remains as it is, human conduct would thus be changed into mere mechanism in which, as in a puppet show, everything would gesticulate well but there would be no life in the figures.”

Kant addresses an age-old question about Christian theology: If God exists and is active in human affairs, why does God’s existence seem so uncertain? Like much of Kant’s philosophy in Critique of Practical Reason, his answer is rooted in the postulate of freedom or free will. If God’s existence were unquestionable and God’s presence were clear to humanity, then there may as well be no free will.

“What, then, really is pure morality, by which as a touchstone one must test the moral content of every action? I must admit that only philosophers can make the decision of this question doubtful, for it is long since decided in common human reason.”

Kant is again asserting here that the moral law is self-evident based on a priori reasoning. At the same time, he is subtly making a jab at speculative reason. Only through pure speculative reason, instead of practical reason, could someone question the existence of a universal moral standard.

“In our times, when one hopes to have more influence on the mind through melting, tender feelings or high-flown, puffed-up pretensions, which make the heart languid instead of strengthening it, than by a dry and earnest representation of duty, which is more suited to human imperfection and to progress in goodness, it is more necessary than ever to direct attention to this method.”

Kant criticizes sensibility, the popular idea among Enlightenment intellectuals that emotions, especially happiness, provide a foundation for morality. Instead, Kant argues that duty is what leads the human mind to the moral law.

“When [respect for ourselves] is well established, when a human being dreads nothing more than to find, on self-examination, that he is worthless and contemptible in his own eyes, then every good moral disposition can be grafted onto it, because this is the best, and indeed the sole, guard to prevent ignoble and corrupting impulses from breaking into the mind.”

Kant argues that rather than conditional emotions, the mental basis for morality is our sense of duty and respect. By this, he not only means respect for moral laws, but respect for the opinions of others.

“Two things fill the mind with ever new and increasing admiration and reverence, the more often and more steadily one reflects on them: the starry heavens above me and the moral law within me.”

Despite his criticism of Hume and speculative philosophy, Kant does not reject empiricism or abstract philosophy entirely, but instead he seeks to create a third way between them, practical reason. This passage invokes that dualism as well as Kant’s view of humans as beings that exist both materially (as phenomena) and in terms of abstract thought (as noumena).