The Critique of Practical Reason () is the second of Immanuel Kant's three critiques, published in 1788. Hence, it is sometimes referred to as the "second critique". It follows on from Kant's first critique, the Critique of Pure Reason, and is one of his major works on moral philosophy. While Kant had already published one significant work in moral philosophy, the Groundwork of the Metaphysics of Morals (1785), the Critique of Practical Reason was intended to develop his account of the will as determinable by (or able to act from) the moral law alone, place his ethical views within the larger framework of his system of critical philosophy, and expand on certain themes in his moral philosophy such as the feeling of respect for the moral law and the concept of the highest good.
Context Kant did not initially plan to publish a separate critique of practical reason. He published the first edition of the Critique of Pure Reason in May 1781 as a "critique of the entire faculty of reason in general"Kant, KrV Axii (viz., of both theoretical and practical reason) and a "propaedeutic" or preparation investigating "the faculty of reason in regard to all pure a priori cognition"Kant, KrV A841/B869 to set up for a metaphysics of nature and a metaphysics of morals.
Next, Kant began work on a metaphysics of morals by writing the Groundwork of the Metaphysics of Morals, published in 1785. Certain remarks in that work show that Kant had changed his mind about the idea of a critique of practical reason. In the Preface, Kant distinguished between a "critique of pure practical reason" and a "critique of pure speculative reason". He also came to think that a metaphysics of morals could only really be founded on the former critique just as a metaphysics of nature needed the latter critique. A critique of pure practical reason, Kant thought, was less necessary than a critique of pure speculative reason since "in moral matters human reason can easily be brought to a high degree of correctness and accomplishment, even in the most common understanding".Kant, GMS 4:391 The third section titled "Transition from metaphysics of morals to the critique of pure practical reason" was written to accomplish what he originally thought was at least partially needed in a critique of pure practical reason to properly set up a metaphysics of morals.
However, Kant then changed his mind again and planned the Critique of Practical Reason as an appendix to the second edition of the Critique of Pure Reason to respond to some of the criticisms made by reviewers and commenters against the latter work. He declared his plan in an announcement he published in the Allgemeine Literatur-Zeitung in November 1786,Kant, Ak. 3:556 but shortly abandoned it and completed the second edition of the Critique of Pure Reason, published in April 1787, without an appended critique of practical reason.
Finally, in June 1787, Kant sent the completed manuscript of his new Critique of Practical Reason to printers in HalleKant, Ak. 10:494 where it was finally published in December 1787Kant, Ak. 10:506 but listed as published in 1788.
Structure of the work The work's structure is based on his earlier text, the Critique of Pure Reason. After a preface and an introduction, the second Critique is split into a Doctrine of Elements and a Doctrine of Method. The former part is further separated into an Analytic and a Dialectic of pure practical reason. The Analytic establishes Kant's theory of practical rationality. There he outlines and analyzes the principles of morality, shows that pure reason is practical (viz. that reason can drive or motivate our actions independently of any empirical conditions lying in the senses and feeling), discusses the object or aim of pure practical reason (the good), and deals with the non-empirical/pure incentives or "motivating springs" (Triebfeder) of morals. The Dialectic is "the exposition and resolution of illusion in the judgments of practical reason",Kant, KpV 5:16. about topics like the highest good and the errors previous philosophers made by putting it as the basis and motivation of morality. It also discusses how the existence of God and the soul's immortality as "postulates of practical reason" fit into the idea of the highest good. The Doctrine of Method discusses moral education and how "one can provide the laws of pure practical reason with access to the human mind and influence on its maxims".Kant, KpV 5:151.
Divisions of the Critique of Practical Reason PrefaceAll section titles are taken from: Introduction Part I. Doctrine of the Elements of Pure Practical Reason Book I. Analytic of Pure Practical Reason Chapter I. On the Principles of Pure Practical Reason §1. Explication (of practical principles) §2–4. Theorems I-III §5–6. Problems I & II §7. Basic Law of Pure Practical Reason (Categorical imperative) §8. Theorem IV a. Practical Material Determining Bases (Rejection of previous philosophical bases of morality) I. On the Deduction of the Principles of Pure Practical Reason II. On the Authority of Pure Reason in Its Practical Use to an Expansion That Is Not Possible for It in Its Speculative Use Chapter II. On the Concept of an Object of Pure Practical Reason a. Table of the Categories of Freedom in Regard to the Concepts of Good and Evil b. Typic of the Pure Practical Power of Judgment Chapter III. On the Incentives of Pure Practical Reason a. Critical Examination of the Analytic of Pure Practical Reason (Comparison with the Critique of Pure Reasons structure and refutations of other theories on freedom of the will) Book II. Dialectic of Pure Practical Reason Chapter I. On a Dialectic of Pure Practical Reason as Such Chapter II. On a Dialectic of Pure Reason in Determining the Concept of the Highest Good I–II. Antinomy of Practical Reason & its Critical Annulment III. On the Primacy of Pure Practical Reason in Its Linkage with Speculative Reason IV-V. The Immortality of the Soul & God's Existence, as Postulates of Pure Practical Reason VI. On the Postulates of Pure Practical Reason as Such VII. How It Is Possible to Think an Expansion of Pure Reason for a Practical Aim without Thereby Also Expanding Its Cognition as Speculative VIII. On Assent from a Need of Pure Reason IX. On the Wisely Commensurate Proportion of the Human Being's Cognitive Powers to His Practical Vocation Part II. Doctrine of the Method of Pure Practical Reason Conclusion
Preface and Introduction Kant sketches out here what is to follow. Most of these two chapters focus on comparing the situation of theoretical and of practical reason and therefore discusses how the Critique of Practical Reason compares to the Critique of Pure Reason.
The first Critique, "of Pure Reason", was a criticism of the pretensions of those who use pure theoretical reason, who claim to attain metaphysical truths beyond the ken of applied reasoning. The conclusion was that pure theoretical reason must be restrained, because it produces confused arguments when applied outside of its appropriate sphere. However, the Critique of Practical Reason is not a critique of pure practical reason, but rather a defense of it as being capable of grounding behavior superior to that grounded by desire-based practical reasoning. It is actually a critique, then, of the pretensions of applied or empirical practical reason.Kant, KpV 5:15-16Angelica Nuzzo, Kant and the Unity of Reason, Purdue University Press, 2005, p. 45-46.
Kant informs us that while the first Critique concluded that God, freedom, and immortality are unknowable on theoretic grounds, the second Critique will mitigate the force this claim on practical grounds. Freedom is revealed by the actuality of practical life because it is revealed by the moral law. God and immortality are also knowable (only on practical grounds), but practical reason now requires belief in these postulates of reason. Kant once again invites his dissatisfied critics to actually provide a proof of God's existence and shows that this is impossible because the various arguments (ontological, cosmological and teleological) for God's existence all depend essentially on the idea that existence is a predicate inherent to the concepts to which it is applied.
Kant insists that the Critique can stand alone from the earlier Groundwork of the Metaphysics of Morals, although it addresses some criticisms leveled at that work (e.g., Pistorius' objection that Kant established the moral principle before the concept of the goodKant, KpV 5:8-9). This work will proceed at a higher level of abstraction.
While valid criticisms of the Groundwork are to be addressed, Kant dismisses many criticisms that he finds unhelpful. He suggests that many of the defects that reviewers have found in his arguments are in fact only in their brains, which are too lazy to grasp his ethical system as a whole. As to those who accuse him of writing incomprehensible jargon, he challenges them to find more suitable language for his ideas or to prove that they are really meaningless. He reassures the reader that the second Critique will be more accessible than the first.
Last, a sketch of the second Critique is then presented in the Introduction. It is modeled on the first Critique: the Analytic will investigate the operations of the faculty in question; the Dialectic will investigate how this faculty can be led astray; and the Doctrine of Method will discuss the questions of moral education.
Analytic: Chapter One Practical reason is the faculty for determining the will, which operates by applying a general principle of action to one's particular situation. For Kant, a practical principle can be either a mere maxim if it is based on the agent's desires or a law if it applies universally. Any principle that presupposes a previous desire for some object in the agent always presupposes that the agent is the sort of person who would be interested in that particular object. Anything that an agent is interested in can only be contingent, however, and never necessary since it is only valid for that agent alone. Therefore, it cannot be a law, but only a maxim.Kant, KpV 5:19-21
To say that the law is to seek the greatest happiness of the greatest number or the greatest good, always presupposes some interest in the greatest happiness, the greatest number, the greatest good, and so on. This cannot be the basis for any universal moral law. Kant concludes that the source of the nomological character of the moral law derives not from its content but from its form alone. The content of the universal moral law, the categorical imperative, must be nothing over and above the law's form, otherwise it will be dependent and based on the desires that the law's possessor has. The only law whose content consists in its form (viz., the form of universality), according to Kant, is the statement:
Kant then argues that a will which acts on the practical law is a will which is acting on the idea of the form of law, an idea of reason which has nothing to do with the senses. Hence the moral will is independent of the world of the senses, the world where it might be constrained by one's contingent desires. The will is therefore fundamentally free. The converse also applies: if the will is free, then it must be governed by a rule, but a rule whose content does not restrict the freedom of the will. The only appropriate rule is the rule whose content is equivalent to its form, the categorical imperative. To follow the practical law is to be autonomous, whereas to follow any of the other types of contingent laws (or hypothetical imperatives) is to be heteronomous and therefore unfree. The moral law expresses the positive content of freedom, while being free from influence expresses its negative content.
Kant then lists and examines six classical moral principles as practical "material" determinants of morality: