Kant's Theoretical Philosophy

Kant's theoretical philosophy is mainly put forward in his “Critique of pure Reason” (CpR, 1781)

1 Initial question: Is metaphysics as a science possible?

2 Conceptual distinction to answer the question:
- necessary - contingent
- A priori (prior to experience) - a posteriori (from experience)
- analytical (predicate contained in subject) - synthetical (predicate not contained in subject)

Metaphysical knowledge has to be: unchangeable, everlasting, and therefore: necessary, a priori. And: it has to be synthetical, because it must tell us something about the way the world is. These a priori synthetical propositions are “mysterious” (although possible for logic, mathematics and physics).

3 The problem with metaphysics
Certain metaphysical questions lead to antinomies (= logical contradicting answers to questions from reason). Kant discusses four antinomies:
1. Thesis: “The world has a beginning in time and is also enclosed within bounds as regards space. Antithesis: “The world has no beginning and no bounds in space [...]” (CpR, A 426, B 454)[1]
2. Thesis: All things are either a) composite out of simple parts or b) not consisting out of simple parts
3. Thesis: “The causality according to laws of nature is not the only causality, from which the appearances of the world can thus one and all be derived. In order to explain these appearances, it is necessary to assume also causality through freedom.” (CpR, A 445, B 473) - Antithesis: “There is no freedom, but everything in the world occurs solely according to laws of nature.” (CpR, A 445, B 473)
4. Thesis: “There belongs to the world something that, either as its part or as its cause, is an absolutely necessary being.” (CpR, A 453, B 481) - Antithesis: “There exists no absolutely necessary being at all, neither in the world nor outside the world, as its cause.” (CpR, A 453, B 481)
Comment I: We necessarily run into these antinomies, when we try to answer a certain type of metaphysical questions. These questions are imposed on humans: “Human reason has a peculiar fate in one kind of its cognitions: it is troubled by questions that it cannot dismiss, because they are posed to it by the nature of reason itself, but that it also cannot answer, because they surpass human reason’s every ability.” (CpR, A vii) Both answers to the question (the thesis and antithesis) can be thought through without contradiction – but they are contradicting one another.
Comment II on the third antinomy: According to the theoretical philosophy of Kant, we cannot know whether there is human freedom. However, in the “Critique of practical reason” (1788) he postulates the existence of immortality, human freedom and God as requirements for practical philosophy.
Note: What cannot be proved by pure, theoretical reason is a presupposition for practical philosophy!

4 Kant’s “Copernican revolution”
Trying to answer metaphysical question, we run into antinomies, therefore we have to concentrate on epistemology (what and how we can know); the subject is primary, and what matters is how we perceive reality, which is structured through our perception. In other words: We can only know about the phenomenal appearances of things, and not know the things themselves; a philosophical theory called “transcendental idealism”.

[1] Kant, Immanuel: Critique of pure reason, trans. Werner S. Pluhar, Indianapolis: Hackett, 1996