Kant's Critique of Pure Reason
II. TRANSCENDENTAL DOCTRINE OF METHOD
Chapter 1: THE DISCIPLINE OF PURE REASON
Section 2: THE DISCIPLINE OF PURE REASON IN RESPECT OF ITS POLEMICAL EMPLOYMENT (p. 593)
Polemical Employment Of Pure Reason: the defense of its propositions against dogmatic counter propositions through which they are denied. Here the contention is not that its own assertions may not be false, but only that no one can assert the opposite with apodeictic certainty, or even with a greater degree of likelihood.
No one can deny these assertions, they can only criticize them.
We cannot allege any misunderstanding such as was found in the antithetic of pure reason where each side was found to be viewing the issue from different points of view (one starting with the things in themselves, the other from appearances), here both are starting from the same place.
Reason benefits by the consideration of its objects from both sides, and its judgment is corrected in being thus limited. What is here in dispute is not the practical interests of reason but the mode of their presentation.
There can be no polemic of pure reason, for how can two persons carry on a dispute about a thing the reality of which neither of them can present in actual or even in possible experience.
He treated concepts of reason (for which no object must necessarily be given in experience) as part of the understanding (which deals with objects of at least possible experience).
He therefore regarded all the supposed a priori principles of these faculties as fictitious.
He was in error in inferring from the contingency of our determination in accordance with the law, to the contingency of the law itself.
He confounded a principle of affinity, which has its seat in the understanding and affirms necessary connection, with a rule of association, which exists only in the imitative faculty of imagination, and which can exhibit only contingent, not objective connections.
The sceptical error Hume made was that he did not make a systematic review of all the various kinds of a priori synthesis ascribable to the understanding.
He merely restricts the understanding without defining its limits.
He draws no distinction between the well grounded claims of the understanding and the dialectical pretensions of reason.
They are merely thought-entities, the possibility of which is not demonstrable.
It is permissible to think the soul as simple in order to infer a necessary unity of its faculties, but it is not permissible to assume it is simple.
A transcendental hypothesis, in which a mere idea of reason is used in explanation of natural existences, would really be no explanation.
To proceed would be to explain something, which in terms of known empirical principles we do not understand sufficiently, by something we do not understand at all.
To employ a transcendental hypothesis and presume we can make good the lack of physical grounds of explanation by appealing to the hyperphysical is to:
Cut off reason from all progress in its own employment.
Deprive reason of all the fruits that spring from the cultivation of its own proper domain, experience.
Using a transcendental hypothesis is committing the error of ignava ratio.
The second requirement for the admissibility of an hypothesis: it must adequately account a priori for those consequences which are [de facto] given.
If we have to resort to additional hypotheses, they each require the same justification as the first.
Reason, when employed apart from all experience can know propositions entirely a priori, or it can know nothing at all.
Hypotheses are not available for the purposes of basing propositions upon them, but they are entirely permissible for the purposes of defending propositions.
i.e. they may not be employed in any dogmatic fashion, but may be employed in polemical fashion.
They may be asserted problematically.
These hypotheses are not intended to strengthen the proof of existence, but only show that one who opposes it has just as weak of an argument.
This would be using reason in its practical employment, not in its speculative employment.
Our opponent has presumed that he has proven the impossibility of our belief based on the lack of empirical evidence and has assumed he has exhausted all possibilities. He is in fact using a hypothesis which has no more ground than our Transcendental hypothesis.
To make principles of possible experience conditions of the possibility of things in general is just as transcendent a procedure as to assert the objective reality of transcendent concepts.
What distinguishes the proofs of transcendental synthetic propositions is that reason may not apply itself, by means of its concepts, directly to the object, but must first establish the objective reality of the concepts, and the possibility of their a priori synthesis.
In transcendental knowledge, so long as we are concerned only with concepts of the understanding, our guide is the possibility of experience.
The proof proceeds by showing that experience itself, and therefore the object of experience, would be impossible without a connection of the kind being shown (for example: cause and effect).
The proof must also show the possibility of arriving synthetically and a priori at some knowledge of things which was not contained in the concepts.
To avoid paralogism, must have a criterion of the possibility of those synthetic propositions which are intended to prove more than experience yields.
This criterion consists in the requirement that proof should not proceed directly to the desired predicate but only by means of a principle that will demonstrate the possibility of extending our given concept in an a priori manner to ideas, and of realizing the latter.
The first rule is, therefore, not to attempt any transcendental proofs until we have considered, with a view to obtaining justification for them, from what source we propose to derive the principles on which the proofs are based, and with what right we may expect success in our inference.
If they are principles of understanding (for instance, causality), it is useless to attempt, by means of them, to attain to ideas of pure reason. Such principles are valid only for objects of possible experience.
If they are principles of pure reason, it is again useless. Reason has principles of its own; but regarded as objective principles, they are all dialectical and can have no validity except as regulative principles.
The second peculiarity of transcendental proofs is that only one proof can be found for each transcendental proposition.
If I am inferring, not from concepts, but from intuition as in mathematics and natural science, the intuition supplies me with manifold material for synthetic propositions so I can start from more than one point and arrive at the same proposition.
In transcendental propositions, I start with one concept only, and assert the synthetic condition of the possibility of the object in accordance with this concept. Since outside this concept there is nothing further through which the object could be determined, there can be only one ground of proof.
The third peculiarity of transcendental proofs is that its proofs must never be apagogical, but always ostensive.
Apagogical Proof: yields certainty by proving the impossibility of the negation of a proposition.
Used in the various sciences when the grounds are too numerous or too deeply concealed.
Permissible only where it is impossible to substitute what is subjective in our representation for what is objective (such as in mathematics).
Never permissible in the enterprises of pure reason, so far as synthetic propositions are concerned because we would have to assert objective validity of the thing in itself when reason can only conceive a thing on subjective grounds.
Ostensive Proof: direct proof which combines with the conviction of its truth insight into the sources of its truth.