Kant’s Philosophy: Practical Reason, Ethics, and Metaphysics
Kant thought that rational human activity is not limited to knowledge of objects; humans also need to know how to act. Reason has a moral function (What do I do?). This dual role of reason is expressed through the distinction between pure and practical reason. Theoretical reason makes judgments, and practical reason makes imperatives and commands.
A universal and rational ethics must be a priori and independent in its requirements; the subject must determine how to act and give itself the law. Therefore, a universal and rational ethic cannot be material but formal, empty of content: it provides no specific goods or purpose. Formal ethics merely indicates how we should always act. A person acts morally when acting out of duty. Based on these assumptions, Kant distinguishes three types of action: breaches of duty, actions in accordance with duty, and actions from duty. Only the latter have moral value. The action is not a means to an end but an end in itself.
The requirement to act morally is expressed in a categorical imperative: act only according to that maxim whereby you can at the same time will that it should become a universal law. The categorical imperative is a formal document because it sets no specific standard for our actions. The formal character of Kantian morality means that the law determines what is good. For this reason, the only permissible motive for the will is the law itself. Hence, the duty to act virtuously, which is worthy of happiness. Kant rejects the idea that happiness can be the determining motive of a good will.
Kantian ethics has certain assumptions, understood as postulates—something not provable but a necessary assumption as a condition of morality itself. One of these postulates is freedom, without which moral autonomy would be impossible. Additionally, neither virtue nor happiness is within immediate reach of humans because we are limited and divided (law vs. desires). Therefore, the relationship between virtue and happiness is problematic. These approaches lead to asserting that morality necessarily postulates the immortality of the soul, the existence of God, and freedom: these are the postulates of practical reason.
Reason is twofold. Kant addresses the theoretical part in the Critique of Pure Reason, explaining how to achieve knowledge of facts and the extent of our knowledge of objects. The solution to the problem of metaphysics is to see if it can adjust to the conditions that enable science. Once these conditions are discovered, Kant investigates the kinds of judgments science uses to understand the transcendental conditions that make them possible. Kantian judgments are analytic or synthetic, a priori or a posteriori. Kant admits the existence of synthetic a priori judgments (JSAP) because synthetic judgments are extensive, and being a priori, they are universal and necessary.
Kant then asks how these judgments are possible in mathematics and physics and whether they are possible in metaphysics. In studying transcendental aesthetic, he examines sensibility and the JSAP in mathematics. Kant says there are two types of sensibility: outer sense and inner sense. Therefore, for sensible knowledge, we need space and time as necessary conditions of sensibility. The JSAP is possible in mathematics due to space and time; as these are properties of the subject, this knowledge is subjective. This initial knowledge is formed by two components: the material element (external sense impressions) and the formal element (a priori forms that structure the reality of the senses). The result is the phenomenon, the sense impression given through space and time categories. In the Transcendental Analytic, he studies understanding and the JSAP in physics. The function of understanding is to understand what is perceived. Understanding phenomena involves referring them to a concept, and this activity is done through judgment. Understanding can be regarded as the power to judge. The a priori forms of understanding, which make understanding possible, are concepts that can be empirical or a priori (also called pure or categories). There are 12 categories of understanding, taking into account quantity, quality, relation, and modality. Understanding phenomena is impossible without applying these categories, but the categories are not applicable to situations beyond experience. The JSAP are the basic principles underlying physics.
The principle of causality is described by Kant as JSAP because the concept of cause is not derived from experience. In the Transcendental Dialectic, he studies reason and the possibility of metaphysics as a science. The function of reason is the unification of knowledge through ideas; its role is to reduce the variety of objects of understanding to the smallest possible number of principles. The principles of reason are pure terms, ideas which are a priori concepts that unify all phenomena. The transcendental ideas of pure reason are the ideas of Soul, World, and God.
Metaphysics deals with the study of the Universe, the Soul, and God using reason. Soul, World, and God are a priori forms of pure reason; we have no sense impression of them, so we cannot form synthetic judgments. Metaphysics is impossible as a science, but it is an inevitable and natural tendency; reason tends to seek the unconditioned, to ask questions and formulate answers about God, the soul, or the world. The ideas of pure reason have a regulative use in the investigation of nature: They set limits that cannot be crossed and drive us to expand the field of research into new experiences and to a greater connection between them.