Kant’s Philosophy: Reason, Morality, and the Categorical Imperative
Kantian Philosophy: Theoretical and Practical Reason
Kantian philosophy is fundamentally divided into two consistent parts. The first, examined in the Critique of Pure Reason, investigates the conditions necessary for human knowledge. The second, discussed in the Critique of Practical Reason, analyzes how morality functions for humans and establishes a formal ethics based on the practical use of reason.
The Critique of Pure Reason: Limits of Knowledge
Kant’s analysis of theoretical reason starts from the premise that neither empiricists (like Hume) nor rationalists (like Descartes or Wolff) were correct in unilaterally identifying the sole source of human knowledge (either experience or reason). For Kant, human knowledge is the fruit of collaboration between both instances.
The Copernican Revolution in Epistemology
The subject is the center of the knowledge process—this is Kant’s famous Copernican Revolution. The process begins with human sensibility, which is the faculty of receiving sense impressions. Sensibility creates an internal image of something perceptible (the phenomenon) from external reality captured through the five senses. Consequently, the reality outside us (the noumenon) is unknowable in principle. This limitation exists not only because our senses are limited, but because we apply a priori structures inherent in our own sensibility—namely, space and time, the forms of all phenomena—to what is perceived. Thus, the phenomenon itself is, from the starting point, a creation (though not ex nihilo) of the subject.
Understanding, Categories, and the Role of Reason
From the phenomenon, our understanding develops empirical concepts (e.g., after seeing several tables, we form the concept “table”). To these phenomena, the understanding applies certain pure a priori concepts that exist in us innately. These concepts are the categories—very general concepts (such as existence, causation, unity) that only make sense when applied legitimately to phenomena. This is their only legitimate use.
The final faculty involved in knowledge is Reason. Reason takes the concepts and judgments made by the understanding and connects them, seeking increasingly general arguments. In its search for the unconditioned, Reason attempts to transcend the limits of phenomenal knowledge, seeking the three ideas of metaphysics: God, Soul, and World. These ideas must never be affirmed as known, as doing so leads to inconsistencies and contradictions. However, they play a crucial role in synthesizing our phenomenal knowledge.
The Critique of Practical Reason: Formal Ethics
In the realm of ethics, the three metaphysical ideas mentioned above come to the fore again, as moral behavior presupposes them. Kant proposed an ethics that does not specifically define what happiness is, unlike traditional material ethics. Kant rejects material ethics because they rely on hypothetical imperatives (e.g., “If you want X, then do Y”), which are conditional and thus devoid of true moral value, as actions are valued only by an external end, not by themselves.
The Categorical Imperative and Moral Autonomy
Kant promotes moral autonomy, requiring every individual to determine if their particular action is consistent with the sole rule of formal ethics: the Categorical Imperative. The most famous formulation is: Act only according to that maxim whereby you can at the same time will that it should become a universal law.
The universalizability of actions is the criterion of rationality and the path toward recognizing every rational being as deserving of the same respect we demand for ourselves. Virtue, in this system, is following the call of duty dictated by the Categorical Imperative.
Virtue, Duty, and the Postulates of Practical Reason
A virtuous life may not necessarily result in a happy life, as empirical beings are dependent on chance circumstances. However, a virtuous life assures the subject recognition of itself as worthy of eternal happiness. This is why Kantian ethics presupposes, without seeking empirical evidence, the three ideas (postulates) of metaphysics: Freedom, Immortality of the Soul, and God.
Metaphysics, both in Kant’s theoretical and moral work, is marked as an unattainable goal for our faculties, yet its presence makes both knowledge and human behavior possible.