Kant’s Physics, Dialectic, and Metaphysics: A Summary
Physics (Pure)
Kant refers only to physical “pure.” Its purpose is to Nature, which means all phenomena. These laws must be synthetic a priori propositions. The problem is this: How do the laws of nature, on whose synthetic character cannot be doubted, be a priori? Indeed, if nature is the set of phenomena, they are subject to the possibility of experience, i.e., the categories; therefore, the rules of use of the categories (understanding) are also laws of Nature. Physics is possible because it is founded on a priori understanding of the categories.
Transcendental Dialectic
“All our knowledge begins with the senses, passes from them to the understanding, and ends with reason. The reason is the supreme power of the unification of knowledge.” But there is no unifying purpose or content itself, but its function is to “reduce” the enormous range of knowledge of understanding to the least number of principles. Hence, reason is called by Kant “the principles.” The “principles” of reason are not propositions first, but initial conditions, which are unconditional. That is, the reason the understanding unifies knowledge refers to something absolutely first and unconditional as “must stop.” These “unconditioned” are called ideas by Kant. Therefore, there are judgments or sentences, but concepts (a priori), which are also called “pure concepts of reason” and “transcendental ideas.”
Ideas are three: soul, world, and God. Its derivation is based on the kinds of reasoning (the same way as the derivation of the categories are made from the table of judgments). There are three kinds of reasoning: categorical, hypothetical, and disjunctive. The ideas of Soul, World, and God unify all the phenomena that the understanding structure using categories. Thus:
- All the phenomena of inner experience are unified by the idea of Alma.
- The phenomena of external experience are unified by the idea of the World.
- Both areas are reduced to one by the idea of God.
Now, using the ideas, we think the totality of the phenomena, but we cannot know that all is unified in the reality of the soul, the world, or God. In conclusion, reason is a faculty of unification through ideas. What unites the variety of knowledge is understanding. But she does not “know” anything. The rule for use of ideas is: do not refer them to never experience, nor that they represent things in themselves; use them only to unify the knowledge of understanding.
Metaphysics
In considering the possibility of metaphysics, Kant has in sight dogmatic rationalist metaphysics, especially that of Wolff. Obviously, the whole development of the Critique of Pure Reason leads to demonstrate their impossibility: It is impossible knowledge of things in themselves (numbers) and in particular, soul, world, and God, and we do not have any such intuition beings. Finally, when Metaphysics proceeds to demonstrations by the principle of causality, it commits a serious fallacy, making an illegitimate use of the categories, to apply to things in themselves which can only be referred to the phenomena.
Thus, metaphysics is impossible as science. However, as a “natural tendency” is absolutely inevitable, even prevent criticism against it. If metaphysics is not possible, then it must then ask what role the ideas of pure reason. Certainly not help us to understand anything. However, the ideas have a regular use of research in Nature, in two ways: 1) negatively, indicating the limits that cannot be transferred, 2) positively, pushing to broaden the scope of research into new experiences. The meaning of this criticism is to show that the unlawful use of the categories of understanding to the things themselves leads to fallacious arguments and conflicting. Metaphysics is impossible as a science but his ideas make sense as postulates of practical reason, soul, freedom, God.