Notes on <Prolegomena to Any Future Metaphysics> - How is Pure Natural Science Possible
Section 14-35
Nature is the existence of things, insofar as that existence is determined according to universal laws. The cognition is not in themselves, since I can not know things apart from my concept. We can not know things in themselves either a priori or a posteriori.
But we have pure natural science, which is a priori and with all of the necessity required of apodidctic propositions, propounds laws to which nature is subject. Here we refer to only to universal natural science, precedes all of physics. For example: that substance remains and persists, that everything that happens always previously is determined by a cause according to constant laws. The question is how are these possible?
Here Nature means the sum total of all objects of experience materially. Cognition of that which cannot be an object of experience would be hyperphysical, and here we are not concerned with such things.
The formal in nature in this narrower meaning is therefore the conformity to law of all objects of experience, and, insofar as this conformity is cognized a priori, the necessary conformity to law of those objects. We can form the question this way:
How is it possible in general to cognize a priori the necessary conformity to law of things as objects of experiences?
Note that we are not talking about rules for the observation of a nature that is already given, which presupposes experience. These laws aren’t a priori. Instead, we are talking about how the a priori conditions of the possibility of experience are at the same time the sources out of which all universal laws of nature must be derived.
Note that not all empirical judgments are judgments of experience. Empirical judgments, insofar as they have objective validity(necessary universal validity), are judgments of experience; those, however, that are only subjectively valid I call mere judgments of perception. The latter do not require a pure concept of the understanding, but only the logical connection of perceptions in a thinking subject. But the former always demand, in addition to the representations of sensory intuition, special concepts originally generated in the understanding, which are precisely what make the judgment of experience objectively valid.
All judgments are first mere judgments of perception, are subjective, and then we give them a new relation to objects, and they also have objective validity because there would be no reason why other judgments necessarily would have to agree with mine, if there were not the unity of the object.
The business of the senses is to intuit; that of the understanding, to think. To think, however, is to unite representations in a consciousness. This unification either arises merely relative to the subject and is contingent and subjective, or it occurs without condition and is necessary or objectives. The unification of representations in a consciousness is judgment. Therefore, thinking is the same as judging or as relating representations to judgments in general. Judgment can be subjective or objective. Experience consists in the synthetic connection of appearances (perceptions) in a consciousness, insofar as this connection is necessary.
Judgments, insofar as they are regarded merely as the condition for the unification of given representations in a consciousness, are rules. And since the formal conditions of judgments that bring the appearances under concepts are necessary for the possibility of experience, these conditions are a priori principles of possible experience. Since principles of experience are also universal laws of nature that can be cognized a priori, the problem of “How is pure natural science is possible” is solved.
Pure physiological table of universal principles of natural science:
- Axioms of intuition
- Anticipation of perception
- Analogies of experience
- Postulates of empirical thinking in general
First and second tables are applications of mathematics to natural science. Relations of appearances are exclusively with regard to their existence. These are not mathematical but dynamical. Appearances must be subsumed under the concept of substance, and an event must be subsumed under the concept of an effect in relation to a cause. Fourth table is about the relation of judgments to experience.
One thing to note is that only objects of experience are all things necessarily subject a priori to these conditions.
Kant also recommends to keep in mind the difference of experience from a mere aggregate of perceptions when we read the proof in analogies of experience(probably referring to the proof of the objective reality of causality).
Hume rightly affirmed that we in no way have insight into the possibility of causality, and Kant added that also the necessity of subject, which could not be predicated of any other thing, and underlie the existence of things. Nonetheless, concept of causality and substance are not illusions, as we have shown above, the principles taken from them stand firm a priori prior to all experience, and have their undoubted objective correctness, though of course only with respect to experience.
I have complete insight into not only the possibility but also the necessity of subsuming all appearances under these concepts(substance, causality, community), i.e., of using them as principles of the possibility of experience.
All synthetic a priori principles are nothing more than principles of possible experience, and can never be related to things in themselves, but only to appearances as objects of experience.
However, we need to keep in mind the concepts of understanding applies only to experience and it is illegitimate to apply them beyond the boundaries of experience. Two important investigations can be found in CPR. One is showing that senses do not apply pure concepts of understanding in concreto, but only the schema for their use. The second investigation is showing that notwithstanding the independence from experience of our pure concepts of the understanding and principles, outside the field of experience nothing at all can be thought by means of them, because they can do nothing but merely determine the logical form of judgment with respect to given intuitions.
How is nature itself possible?
This question is the highest point that transcendental philosophy can ever reach. It contains two questions. First, how is nature possible in general in the material sense, namely, according to intuition, as the sum total of appearances. The answer is: by means of the constitution of our sensibility. The answer is given in Transcendental Aesthetic in CPR. Second question, how is nature possible in the formal sense, as the sum total of the rules to which all appearances must be subject if they are to be thought as connected in one experience? The answer is: by means of the constitution of our understanding. This answer is given in Transcendental Logic in CPR.
The highest legislation for nature must lie in our self, i.e., in our understanding, and that we must not seek the universal laws of nature from nature by means of experience, but, conversely, must seek nature, as regards its universal conformity to law, solely in the conditions of the possibility of experience that lie in our sensibility and understanding. Such agreement, and indeed necessary agreement, between the principles of possible experience and the laws of the possibility of nature, can come about from only two causes: either these laws are taken from nature by means of experience, or, conversely, nature is derived from the laws of the possibility of experience in general and is fully identical with the mere universal lawfulness of experience. The first one contradicts itself, for the universal laws of nature can and must be cognized a priori (i.e., independently of all experience) and set at the foundation of all empirical use of the understanding; so only the second remains. The understanding does not draw its (a priori) laws from nature, but prescribes them to it.
Appendix: On the system of categories
In the appendix, Kant talks about the origin of his categories of understanding.