The Critique of Practical Reason

by Immanuel Kant
Start Free Trial


Download PDF PDF Page Citation Cite Share Link Share

Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 328

None of Immanuel Kant’s writings can be understood without a clear recognition of the “Copernican revolution” in philosophy effected by his first critique, Kritik der reinen Vernunft (1781; The Critique of Pure Reason, 1838). Previously, the predominant rational tradition in Western philosophy was founded on the assumption of reason’s capacity for discovering the forms or essential structures characterizing all things. Whether the form of “treeness” was an innate aspect of every existent tree (as Greek philosopher Aristotle believed) or a transcendent form in which each existent tree participated (as Greek philosopher Plato held), the capacity of reason for perceiving such forms was not doubted. The medieval controversy over “universals” centered not in reason’s ability for such perception but in the nature of this rational activity.

See eNotes Ad-Free

Start your 48-hour free trial to get access to more than 30,000 additional guides and more than 350,000 Homework Help questions answered by our experts.

Get 48 Hours Free Access

From the first questioning of the nominalists, however, through the break between self and “exterior world” in the philosophy of René Descartes, doubt as to the precise authority of rational apprehension increased. Human error and empirical deception began to be seen as intervening between perceiver and perceived, thus raising powerfully the question of the criteria for truth. The Aristotelians, especially from the time of Saint Thomas Aquinas on, affirmed that knowledge begins with sense perception; however, because of reason’s capacity for extracting forms, human knowledge not only possessed the qualities of necessity and universality but also made possible an inductive knowledge of trans-empirical realities.

It was the empiricists, especially David Hume, who provided the most serious challenge to this rationalist claim. Centering his attack on the problem of universal causality (cause and effect as universally operative), Hume raised the question of necessity. On what grounds, he asked, can one insist that, of necessity, all “effects” have causes and, similarly, that such causes necessarily produce identical effects? Hume’s conclusion was that the category of causality, like all human ideas, is derived from sense impressions, having the status simply of a habitual assumption and expectation; human ideas are forever bereft of necessity.

Answering the Empiricists

Download PDF PDF Page Citation Cite Share Link Share

Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 628

It was Kant who saw the seriousness of this empiricist challenge. Reason was bankrupt as an agent of knowledge if it could no longer claim necessity, and thus universality, for its findings. Humanity and the world had been severed, and skepticism seemed the inevitable result.

The answer provided by Kant’s first critique was a revolution, a complete reversal of the previous conception of the knowing process. If human knowledge cannot claim a necessity that is resident within the empirical world itself, it is possible, nevertheless, to claim universality for it if the locus of necessity is within the universal operations of human reason. With this new conception of rational necessity and universality, Kant proceeded to exhibit what he conceived to be the necessary operations of rational apprehension, the manner in which the understanding, by its very structure, has perceived and organized, and of necessity will always perceive and organize, whatever realities encounter it.

As Kant interpreted it, Hume’s error was in seeing subjective necessity as grounded only in habit instead of being a result of the a priori structure of reason. If the latter is the case, rational necessity and universality are guaranteed, although on a far different basis from before. For Kant, the forms perceived through sense experience are the product of the categories of the human mind, but now the externality so encountered is never known as it is in itself (as noumenon), but only in its relation to humanity (as phenomenon).

Although reason attempts to complete this knowledge by bringing it into a comprehensive unity, it is barred from success in this speculative operation by certain antinomies, both sides of which are in harmony with a person’s phenomenal knowledge. In the area of speculative psychology, these antinomies make it impossible to affirm a soul existing apart from the physical. In the area of speculative cosmology, the consequence of the antinomies centers in the impossibility of establishing human beings as free of the determined processes of cause and effect. In the area of speculative theology, the antinomies negate the possibility of proving the existence of God. In all cases, the antinomies defy resolution of these questions either positively or negatively.

As a result, reason, in its theoretical function, is barred from any cognitive penetration into the noumenal. This does not mean that the noumenal realm is necessarily unlike a person’s phenomenal knowledge of it and that human categories do not apply there; rather, the problem is that pure reason can provide no guarantee of any correspondence.

What is most significant about the first critique is that, while Kant revives the old Platonic distinction between noumenon and phenomenon, as he explored reason along the narrowly Aristotelian lines of his day (as a strictly cognitive activity), the Platonic distinction became a severe human limitation. Plato had stressed the noetic aspects of reason, which was deeply imbued with an intuitive or mystical quality. However, in the preface to the second edition of the first critique, Kant gave indication that he was moving toward a broader, or more Platonic, conception of reason: “I have found it necessary to deny knowledge [of supersensible reality] in order to make room for faith.” Although faith, for Kant, was to be understood largely in moral terms (stemming from his pietistic background), we have here a beginning indication of his recognition of modes of human apprehension far broader than simply discursive or cognitive reason. Much of the impetus for exploring this possibility came from Kant’s tremendous interest in ethics, made urgent by the seemingly undermining affect of his first critique upon this realm. His understanding of the experience of the form of duty, like Plato’s experience of the form of the good, has about it a near mystical quality.

Pure vs. Practical Reason

Download PDF PDF Page Citation Cite Share Link Share

Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 311

The Critique of Practical Reason is of major importance not only as the attempt to create a purely rational ethic but also as a defense of a nondiscursive mode of apprehension, as an insistence that the “rational” is not restricted in meaning to the “cognitive.” It is this point that Kant develops further in the third critique, Kritik der Urteilskraft (1790; The Critique of Judgment, 1892), in terms of beauty and the purposiveness of nature. In order to understand these points, one must beware the misleading title of the second critique. In distinguishing between pure reason and practical reason, Kant is not speaking of two human agents or loci of activity; in both critiques he is speaking of pure reason as such, but in the first he is concerned with its theoretical or speculative function, in the second with its practical or ethical function. For Kant, this second function is the activity known as will. It is his purpose to show that will is not divorced from reason, controlled internally by drives or impulses, or externally by pleasure stimuli. In its fulfilled operation, it is a purely rational enterprise; it is pure reason in its practical operation which must control drives and determine external ends.

Likewise, in this realm it was Hume who haunted Kant, for Hume understood reason as being the pawn of passions, and morality as being rooted in subjective feeling. Just as Kant’s answer in the cognitive realm depended on exhibiting the a priori or categorical laws of human cognitive activity, so his answer in the second critique depended on discovering the a priori or categorical laws of the rational will. Morality could claim objectivity and universality only by being founded not on experience but on pure reason itself. The task of the second critique, then, is to discover the a priori or necessary principles of the practical reason.

The Problem of Freedom

Download PDF PDF Page Citation Cite Share Link Share

Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 508

At the heart of the problem of ethics is the problem of freedom; without freedom, morality is an impossibility. However, according to the first critique, since all things are seen, of necessity, under the category of causality, all things are seen as determined. Yet, Kant insists, the same noumenon-phenomenon distinction applying to the object of such knowledge applies to the subject as well. It is humanity as phenomenon who is seen under the category of necessity, but the nature of the noumenal person remains unknown. Although the speculative function of reason strives for an understanding of the human “soul,” the antinomies, as we have seen, left the matter of freedom for the noumenal self as “problematic but not impossible.” If Kant can exhibit the will as free, he believes, he can also show the capacity of pure reason to determine the will’s total activity.

If there is to be an objective ethic, an ethic based on freedom, the only possibility for it can be reason presupposing nothing else but itself, for a rule can be objective and universal only if it is not subject to any contingent, subjective conditions. Thus, moral laws cannot be based on the pleasure principle, for the objects of pleasure and pain can be identified only empirically, thus having no objective necessity. Further, hedonism can make no legitimate distinction between higher and lower pleasures; only if reason is able to determine the will can there be a higher faculty of desire than base feeling. Likewise, there is no objective, universal basis for an ethic of happiness, for happiness is simply the general name for satisfaction of desire.

Consequently, maxims (subjective, personal principles) of people’s commonplace activity can claim the ethical status of law not according to their content, which is always empirically gained, but only according to their form. Every maxim can be tested for such universality of form by inquiring whether that maxim, if made a universal law, would negate itself. For example, all people seeking only their own happiness would soon render happiness impossible; thus, the goal of individual happiness is judged to be lacking the universality required of a moral law.

Now, since it is only the form of the maxim that makes objective claim upon the will, the will must be seen as independent of the natural law of cause and effect; that is, we have here a case in which the will operates in isolation from the phenomenal realm. The act is rooted totally in reason itself. This is the heart of Kant’s ethic—”freedom and unconditional practical law imply each other.” Since freedom cannot be known through the theoretical function of reason, its objective reality is discovered by experiencing the moral law as duty, as a rational necessity. This means that the pure practical laws are discovered in the same manner as the pure theoretical laws, by observing what reason directs in indifference to empirical conditions. Without the moral law, Kant insists, people would never know themselves to be free; “thou ought” implies “thou canst.”

The Categorical Imperative

Download PDF PDF Page Citation Cite Share Link Share

Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 385

For Kant, the fundamental law of the pure practical reason is this: “So act that the maxim of your will could always hold at the same time as a principle establishing universal law.” Such rational control of the will is objective, for the legislation is made in indifference to any contingencies. Yet a distinction must be drawn between a pure will and a holy will; although the moral law is a universal law for all beings with reason and will, because the free person has wants and sensuous motives, that person is capable of maxims that conflict with the moral law. Thus, this law comes to people as a “categorical imperative.” It is categorical because it is unconditioned; it is an imperative because it is experienced as “duty,” as an inner compulsion provided by reason. Holiness is above duty, but in this life it remains the ideal to be striven for, but never reached. Each maxim must strive for unending progress toward this ideal; it is such progress that deserves the name “virtue.”

Kant’s formulation of the moral law is, in effect, a philosophical statement of the Golden Rule. As Kant says, the moral law of universality alone, without the need of any external incentive, arises as duty “to extend the maxim of self-love also to the happiness of others.” Put on a commonsense level, Kant’s moral formula is rooted in the integrity required by reason. It is self-evident that reason, to be rational, must operate in complete self-consistency; since the rational is the universal, reason qua reason must consent to will only that which can consistently be willed universally.

For Kant, the demand of duty is unmistakable and can, without difficulty, be perceived by the simplest person. Where the difficulty arises is in following the imperative. Kant’s estimate of humanity is such that he goes so far as to maintain that the good act is done only when duty and inclination are in conflict. What he really means here is that aversion is a sign that the individual has gone beyond self-interest to real duty. It is necessary to insist, Kant maintains, that satisfaction follows but does not precede awareness of the moral law; there is certainly a “moral feeling” that should be cultivated, but duty cannot be derived from it.

Six Ethical Systems

Download PDF PDF Page Citation Cite Share Link Share

Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 613

Kant’s rejection of all ethical theory but his own formal principle provides a helpful summary of alternative ethical systems. Of the subjective type, there are two kinds: external and internal. In the former, philosophers such as Michel de Montaigne root ethics in education, while others, such as Bernard Mandeville, see its basis in a civil constitution. Of the internal variety, Epicurus sees physical feeling as central, while Francis Hutcheson grounds ethics in “moral feeling.” There are likewise internal and external types within the objective ethical systems. The former is the ethic of perfection, held by Christian von Wolff and the Stoics; the latter is the “will of God” ethic of theological morality. The subjective group Kant quickly discards as empirically based and thus, by definition, failing to meet the requirements of universal morality. Also, the objective types, though rational, depend on a content that, within the confines of Kant’s first critique, can be gained by empirical means only; consequently, these too must be disqualified as neither universal nor necessary.

People’s capacity for obeying the moral law in independence of empirical conditions establishes, for Kant, the objective fact of their free, supersensible (noumenal) nature. As Kant puts it, the necessity of the practical reason makes freedom a rational postulate. Freedom is not known, in the theoretical sense, but it must be subjectively affirmed as necessary. This does not mean that freedom is simply subjective, but that its objectiveness is perceived through reason’s practical rather than theoretical operation. Moral need has the status of law, while the antinomies render the completions of speculative reason hypothetical or arbitrary. Thus, the former provides the certitude that the latter lacks, establishing the factuality of freedom as valid for both the practical and pure reason. Here we see the breadth of Kant’s conception of reason: Such a moral postulate is both objective and rational, even though it is not cognitive.

Because it is Kant’s concern to show that it is pure (speculative) reason itself that is practical, the postulates of reason in its practical function become objective for reason as such. In actuality, the practical function is prior and the speculative function must submit to it, for “every interest is ultimately practical, even that of speculative reason being only conditional and reaching perfection only in practical use.” The result of this insight is that the agnosticism of the first critique is transcended by the second, for while still insisting upon his former severe limitations on speculative reason, Kant here provides an alternative mode for metaphysical affirmation. This is most apparent in the two additional moral postulates that Kant draws from the postulate regarding freedom. What is required by the moral law is complete “fitness of intentions,” which would be holiness. However, since this is impossible for finite humanity, the practical reason requires that one affirm an “endless progress” in which such fitness can be completed. Because such progress requires the immortality of the soul, this affirmation becomes an objective postulate of the practical reason. Such a proposition is not demonstrable, but is “an inseparable corollary of an a priori unconditionally valid practical law.” Thus the second antinomy of speculative reason is practically resolved.

Likewise, a third postulate is involved. The postulate of immortality can be made only on the supposition of a cause adequate to produce such an effect; thus, one must affirm as an objective postulate the existence of God, an affirmation sharing the same necessary status as the other two moral postulates. A further basis for this postulate rests in the fact that although finite existence supports no necessary connection between morality and proportionate happiness, such a connection is morally necessary.

Pure Rational Faith

Download PDF PDF Page Citation Cite Share Link Share

Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 352

The affirmation of such postulates Kant calls the activity of “pure rational faith,” for although they are objective (necessary), freedom, the soul, and God are not known as they are in themselves. This, he affirms, is in truth the essence of “the Christian principle of morality.” It is from morality that religion springs, for religion is nothing more than “the recognition of all duties as divine commands.”

Because morality involves the moral law, with the form of an action, it follows that no “thing” is good or evil; such designations properly apply only to an acting will. Good and evil are defined only after and by means of the moral law; to reverse this procedure is to develop an empirical, subjective ethic. It is the practical judgment that determines the applicability of a universal maxim to a concrete act. To make an application such as this is very difficult, for it is here that the laws of freedom (the noumenal realm) are applied to the laws of nature (the phenomenal realm). Such a meeting is possible because the moral law is purely formal in relation to natural law. That is, it raises this question: If this proposed act should take place by a law of nature of which you were a part, would your will regard it as possible? The center of the moral act thus rests in one’s intentions, not in consequences. If the right act occurs but not for the sake of the moral law, it is not a moral act. The only incentive that is valid is the moral law itself.

For human beings as they are, their natural feelings of self-love are ever at war with the moral law. The very fact that morality resides in law reveals the severe “limitation” of humanity. The moral law is victorious only if all inclinations and feelings are set aside out of respect for the moral law, in and of itself. An act not performed out of such a sense of duty is inevitably tainted with the self-pride of believing goodness to be a spontaneous reflection of one’s nature.

Problems of Application

Download PDF PDF Page Citation Cite Share Link Share

Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 317

Perhaps the major difficulty in Kant’s ethic is the problem of application. There are few acts that a performer would not defend as universally valid if the hypothetical performer and situation were in every way identical with those of the actual performer. Every evil has been defended by the exigencies of person and circumstance. Kant’s moral formula is designed to eliminate all such individualized decisions. Yet to the degree that the formula is interpreted, not in such a particularized fashion but in an absolutely universal sense, its inadequacy becomes evident. Total truth-telling, total promise-keeping, and the like, all have obvious moral exceptions. Likewise, how is one to resolve conflicts between these objective duties? Furthermore, law for its own sake tends to be elevated above the individual persons between whom moral relations arise.

Kant’s moral position has stimulated generations of heated conflict. For certain theologians, Kant’s ethic seems to be only an ethic of the Fall and not a redemptive ethic; for others, it is a classic Protestant ethic, judging human pretension and incapacity. For philosophers, the difficulty, as with Saint Anselm’s ontological argument, rests in its deceptive simplicity (despite the difficulty of its expression). Such a position is uncomfortable in its rather wholesale rejection of consequences, moral incentives, absolute good, and the like. However, there is no denying Kant’s realistic appraisal of human capacity, the absolute quality of moral activity and yet the relativity of concrete ethical situations. It may be that Kant’s ethic is too simple, discards too much, and is too uncompromising, but consequent ethicists have found it impossible to bypass this second critique.

In regard to their larger ramifications, Kant’s critiques have been a powerful damper on speculative metaphysics. Philosophically, they have stimulated an exploration of noncognitive modes of human apprehension; theologically, they have encouraged exploration of the moral dimensions of religion and of theological method.


Download PDF PDF Page Citation Cite Share Link Share

Last Updated on May 6, 2015, by eNotes Editorial. Word Count: 468

Additional Reading

Allison, Henry E. Idealism and Freedom: Essays on Kant’s Theoretical and Practical Philosophy. New York: Cambridge University Press, 1996. An important interpreter of Immanuel Kant explores relationships between Kant’s theory of knowledge and his moral philosophy.

Bohman, James, and Matthias Lutz-Backmann, eds. Perpetual Peace: Essays on Kant’s Cosmopolitan Ideal. Cambridge, Mass.: MIT Press, 1997. The contributors appraise Kant’s theories about and hopes for a universal rationality that would encourage shared moral understanding and reduce political conflict.

Cassirer, Ernst. Kant’s Life and Thought. Translated by James Hayden. New Haven, Conn.: Yale University Press, 1981. Written by an important twentieth century philosopher, this book offers a readable intellectual biography of Kant.

Caygill, Howard. A Kant Dictionary. Cambridge, Mass.: Blackwell, 1995. A reliable reference guide that helps to clarify key concepts and ideas in Kant’s philosophy.

Copleston, Frederick. A History of Philosophy: Modern Philosophy. Garden City, N.Y.: Doubleday, 1964. Copleston devotes several lucid chapters to Kant and his significance in the history of philosophy.

Guyer, Paul. Kant and the Claims of Taste. New York: Cambridge University Press, 1979. A careful and detailed study focusing on Kant’s understanding of beauty and goodness and how we make judgments about them.

Guyer, Paul, ed. The Cambridge Companion to Kant. Cambridge, England: Cambridge University Press, 1992. Helpful essays by contemporary Kant scholars shed important light on key aspects of Kant’s theory of knowledge, metaphysics, ethics, and religious thought.

Hare, John E. The Moral Gap: Kantian Ethics, Human Limits, and God’s Assistance. New York: Oxford University Press, 1996. A study of the strengths and weakness of Kant’s influential moral philosophy.

Jones, W. T. A History of Western Philosophy: Kant to Wittgenstein and Sartre. New York: Harcourt, Brace, 1969. Provides a good starting point for readers who want a clear and basic introduction to Kant’s philosophy.

Kemp, John. The Philosophy of Kant. New York: Oxford University Press, 1968. A brief, readable account of Kant’s theory of knowledge, moral philosophy, and aesthetics.

Kuehn, Manfred. Kant: A Biography. New York: Cambridge University Press, 2001. The first major biography of the philosopher in fifty years. Includes extensive notes and a bibliography.

Schönfeld, Martin. The Philosophy of the Young Kant: The Precritical Project. New York: Oxford University Press, 2000. A study of the philosopher’s work before the Critique of Pure Reason.

Schott, Robin May, ed. Feminist Interpretations of Immanuel Kant. University Park: Pennsylvania State University Press, 1997. Essayists bring the perspectives of feminist scholarship to bear on Kant’s method and thought.

Walker, Ralph. Kant. New York: Routledge, 1999. An excellent biographical introduction to the thoughts of the philosopher, clearly presented and requiring no special background. Bibliography.

Wolff, Robert Paul, ed. Kant: A Collection of Critical Essays. Garden City, N.Y.: Doubleday, 1967. Important scholars contribute essays on a wide range of themes and issues in Kant’s philosophy.

See eNotes Ad-Free

Start your 48-hour free trial to get access to more than 30,000 additional guides and more than 350,000 Homework Help questions answered by our experts.

Get 48 Hours Free Access