47 pages • 1 hour read
Immanuel KantCritique of Practical Reason
Nonfiction | Book | Adult | Published in 1788A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Preface-IntroductionChapter Summaries & Analyses
Preface Summary
In the Preface, Immanuel Kant declares his intent is to demonstrate the existence of what he calls “pure practical reason.” However, he also suggests that the term is redundant, as any use of reason that is practical, meaning it “proves its reality and that of its concepts by what it does”, is by definition pure. This is in contrast to abstract or “speculative” reason, which is not pure in of itself but can be pursued in a way that is pure, meaning detached from any experiential evidence. The differences between practical and speculative reason are shown in the case of freedom. Under speculative reason, one can question the existence of free will, a degree of skepticism that, in Kant’s view, would deprive life of all meaning. Through practical reason, however, freedom’s objective reality is shown through “the moral law.” In addition, Kant argues that the existence of free will is proven through a priori reasoning, by which he means that we intuitively know that free will exists. Similarly, the existence of abstract concepts of God and immortality is revealed to an individual’s will through moral law. Speculative reason can provide possible and “subjective” insights into the nature of God and immortality. However, speculative reason alone cannot actually prove the existence of God and immortality. Because the human faculty of speculation is naturally prone to error, it is necessary to link these concepts to the practical or “moral use of reason” (5).
Speculative reason is of limited utility because it relies on “supersensible” (5) categories, by which Kant means things that we can never understand through empirical evidence and our bodily senses. By using practical reason in conjunction with speculative reason, one can avoid the trap of extreme skepticism, which Kant describes as “not taking everything supersensible as a fiction and its concept as empty of content” (5). On the other hand, practical reason reveals the existence of freedom, which for Kant means the Freedom of the Will, as well as the fact that causality (the consequences and effects of choices made by individuals) begins with that freedom. Based on this, Kant argues that the Critique of Practical Reason will address two points critics have raised about his earlier treatise, the Critique of Pure Reason. The first point is that even “noumena,” things that can only be understood outside the bodily senses, can nonetheless be described through categories that are “objective.” The second is that an individual can be a “noumenon” in the sense that they understand themselves as having freedom of will, but each individual is also a “phenomenon” (5) in that they are understood through their own and other people’s bodily senses.
Kant rejects certain criticisms of his prior work, among them the complaint that his writing style was so complicated that he was accused of trying to “introduce a new language” (8). At the same time, Kant does note that he has taken certain criticisms of his past works to heart. He writes that his goal in Critique of Practical Reason is to understand “a particular faculty of the human soul” (8) by beginning with the parts of it, through which the whole can be understood.
Kant anticipates a counterargument to his thesis: Some might argue that there is “no a priori cognition at all” (9). Kant rejects this counterargument as logically untenable, as this “would be tantamount to someone wanting to prove by reason that there is no reason” (9). To claim that there is no a priori cognition would be to make a claim that applies universally, and making such a claim is impossible through the empirical reasoning that would have to be the basis of such a statement. Further addressing the philosopher David Hume, who questioned whether one can truly know the cause of anything, Kant turns to mathematics. Specifically, Kant asserts that mathematics proves that an empirical understanding of an object sometimes also requires “synthetic” reason, meaning reason that also examines the ways in which the experience of something is felt and understood. For example, Kant points out that knowledge gained through the senses suggests that space is not infinitely divisible, but mathematics proves that it is (10-11).0
Introduction Summary: “On the Idea of a Critique of Practical Reason”
Kant discusses his last treatise, the Critique of Pure Reason, which dealt purely with abstract ideas. In contrast, practical reason deals with objects that can be experienced through the senses and with causality, meaning the influence that one object or event has on another object or event. Also, Kant argues that the Freedom of the Will proves that pure reason “is unconditionally practical” (12). Finally, Kant lays out how he will discuss practical reason, most specifically stating that he will have to begin with showing how freedom of the will leads to causality.
Preface-Introduction Analysis
In part, Kant’s preface is meant to address critics of his last work, Critique of Pure Reason, and explain how Critique of Practical Reason will build on and further justify arguments from Critique of Pure Reason. Kant addresses the work of the empiricist philosopher David Hume and what Kant describes as a “system of universal empiricism” that would, at least according to Kant, deprive life of meaning. Both topics lead Kant to The Limits of Speculative Reason. As in his previous work, Kant claims that abstract or speculative reason alone is insufficient to prove the existence of metaphysical concepts like God the afterlife. On the other hand, Hume’s argument that personal, sensory experience is the superior or even the only way to gain knowledge has undermined traditional Western arguments about all metaphysical questions. If philosophical standards demand evidence based on sensory experience, then the existence of God cannot be proven.
In his argument with Hume, Kant concedes that abstract reasoning alone is insufficient, but he does not concede that God’s existence is therefore unprovable. Kant regards Hume’s skepticism as untenable and morally dangerous, and his intention in this book is to offer another form of reasoning—one that is neither “speculative” nor solely reliant on sensory experience. He calls this alternative mode “practical reason.”
A key part—perhaps the most important part—of Kant’s thesis in Critique of Practical Reason is the existence of free will. In Kant’s philosophy, Freedom of the Will offers logical proof that human beings have been created by and in the image of God. Humans are rational beings who can think creatively and abstractly and can act in ways that change the world around them. As such, they bridge the gap between phenomena (things experienced through the senses) and noumena (things experienced only through thought). Kant sees this as proof that—contra Hume—causality does objectively exist. He describes free will as “a faculty either of producing objects corresponding to representations or of determining itself to effect such objects (whether the physical power is sufficient or not)” (12). In other words, because people can choose how to influence the world around them, free will must exist. The fact that humans can have an abstract thought (an image of an alien being) and act upon that thought with cause and effect (drawing a picture of that image of the alien being) is the cornerstone of Kant’s entire idea of practical reason, which concerns abstract and speculative ideas but also moral actions that affect the material world. From the existence of free will, which Kant takes as a logical certainty that is also proven through everyday experience, Kant believes he has also addressed Hume’s problem with causality. Further, Kant will draw on the certainty of free will and the idea of practical reason to argue his other postulates, the immortality of the soul and the existence of God.
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