The first rule for our guidance is, therefore, not to attempt a transcendental proof, before we have considered from what source we are to derive the principles upon which the proof is to be based, and what right we have to expect that our conclusions from these principles will be veracious.If they are principles of the understanding, it is vain to expect that we should attain by their means to ideas of pure reason; for these principles are valid only in regard to objects of possible experience.If they are principles of pure reason, our labour is alike in vain.For the principles of reason, if employed as objective, are without exception dialectical and possess no validity or truth, except as regulative principles of the systematic employment of reason in experience.But when such delusive proof are presented to us, it is our duty to meet them with the non liquet of a matured judgement; and, although we are unable to expose the particular sophism upon which the proof is based, we have a right to demand a deduction of the principles employed in it;and, if these principles have their origin in pure reason alone, such a deduction is absolutely impossible.And thus it is unnecessary that we should trouble ourselves with the exposure and confutation of every sophistical illusion; we may, at once, bring all dialectic, which is inexhaustible in the production of fallacies, before the bar of critical reason, which tests the principles upon which all dialectical procedure is based.The second peculiarity of transcendental proof is that a transcendental proposition cannot rest upon more than a single proof.If I am drawing conclusions, not from conceptions, but from intuition corresponding to a conception, be it pure intuition, as in mathematics, or empirical, as in natural science, the intuition which forms the basis of my inferences presents me with materials for many synthetical propositions, which I can connect in various modes, while, as it is allowable to proceed from different points in the intention, I can arrive by different paths at the same proposition.
But every transcendental proposition sets out from a conception, and posits the synthetical condition of the possibility of an object according to this conception.There must, therefore, be but one ground of proof, because it is the conception alone which determines the object; and thus the proof cannot contain anything more than the determination of the object according to the conception.In our Transcendental Analytic, for example, we inferred the principle: Every event has a cause, from the only condition of the objective possibility of our conception of an event.This is that an event cannot be determined in time, and consequently cannot form a part of experience, unless it stands under this dynamical law.This is the only possible ground of proof; for our conception of an event possesses objective validity, that is, is a true conception, only because the law of causality determines an object to which it can refer.Other arguments in support of this principle have been attempted- such as that from the contingent nature of a phenomenon;but when this argument is considered, we can discover no criterion of contingency, except the fact of an event- of something happening, that is to say, the existence which is preceded by the non-existence of an object, and thus we fall back on the very thing to be proved.If the proposition: "Every thinking being is simple," is to be proved, we keep to the conception of the ego, which is simple, and to which all thought has a relation.The same is the case with the transcendental proof of the existence of a Deity, which is based solely upon the harmony and reciprocal fitness of the conceptions of an ens realissimum and a necessary being, and cannot be attempted in any other manner.
This caution serves to simplify very much the criticism of all propositions of reason.When reason employs conceptions alone, only one proof of its thesis is possible, if any.When, therefore, the dogmatist advances with ten arguments in favour of a proposition, we may be sure that not one of them is conclusive.For if he possessed one which proved the proposition he brings forward to demonstration-as must always be the case with the propositions of pure reason-what need is there for any more? His intention can only be similar to that of the advocate who had different arguments for different judges; this availing himself of the weakness of those who examine his arguments, who, without going into any profound investigation, adopt the view of the case which seems most probable at first sight and decide according to it.
The third rule for the guidance of pure reason in the conduct of a proof is that all transcendental proofs must never be apagogic or indirect, but always ostensive or direct.The direct or ostensive proof not only establishes the truth of the proposition to be proved, but exposes the grounds of its truth; the apagogic, on the other hand, may assure us of the truth of the proposition, but it cannot enable us to comprehend the grounds of its possibility.The latter is, accordingly, rather an auxiliary to an argument, than a strictly philosophical and rational mode of procedure.In one respect, however, they have an advantage over direct proofs, from the fact that the mode of arguing by contradiction, which they employ, renders our understanding of the question more clear, and approximates the proof to the certainty of an intuitional demonstration.
