Immanuel Kant's Critique of Pure Reason — trans. F. Max Müller

Discipline of Pure Reason 633

and a necessary Being, and cannot be found anywhere else.

By this caution the criticism of the assertions of reason is much simphfied. Wherever reason operates with concepts only, only one proof is possible, if any. If therefore we see the dogmatist advance with his ten proofs, we may be sure that he has none. For if he had one which (as it ought to be in all matters of pure reason) had apodictic power, what need would he have of others .^ His object can only be the same as that of the parliamentary lawyer who has one argument for one person, and another for another. He wants to take advantage of the weakness of the judges, who, without enquiring more deeply, and in order to get away as soon as possible, lay hold of the first argument that catches their attention, and decide accordingly.

The third peculiar rule of pure reason, if it is once subjected to a proper discipline with regard to transcendental proofs, is this, that such proofs must never be apagogical or circumstantial, but always ostensive or direct. The direct or ostensive proof combines, with regard to every kind of knowledge, a conviction of its truth with an insight into its sources ; the apagogical proof, on the contrary, though it may produce certainty, cannot help us to comprehend the truth in its connection with the grounds of its possibility. It is therefore a mere ex- [p. 790] pedient, and cannot satisfy all the requirements of reason. The apagogical proofs have, however, this advantage with regard to their evidence over direct proofs, that contradiction always carries with it more clearness in the representation than the best combination, and thus approaches more to the intuitional character of a demonstration.

634 Discipline of Pure Reason

The real reason why apagogical proofs are so much employed in different sciences, seems to be this. If the grounds from which some knowledge is to be derived are too numerous or too deeply hidden, one tries whether they may not be reached through their consequences. Now it is quite true that this modus ponens, that is, this inferring of the truth of some knowledge from the truth of its consequences, is only permitted, if all possible consequences flowing from it are true. In that case they have only one possible ground, which therefore is also the true one. This procedure, however, is impracticable, because to discover all possible consequences of any given proposition exceeds our powers. Nevertheless, this mode of arguing is employed, though under a certain indulgence, whenever something is to be established as a hypothesis only, in which case a conclusion, according to analogy, is admitted, namely, that if as many consequences as one has tested agree with an assumed ground, all others will also agree with it. To change in this way a hypothesis into a demonstrated truth, is clearly impossi- [p. 791] ble. The modus tollens of reasoning, from consequences to 'their grounds, is not only perfectly strict, but also extremely easy. For if one single false consequence only can be drawn from a proposition, that proposition is wrong. Instead, therefore, of examining, for the sake of an ostensive proof, the whole series of grounds that may lead us to the truth of a cognition by means of a perfect insight into its possibility, we have only to prove that one single consequence, resulting from the opposite, is false, in order to show that the opposite itself is false, and therefore the cognition, which we had to prove, true.

This apagogical method of proof, however, is admissible

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in those sciences only where it is impossible \.o foist the subjective elements of our representations into the place of what is objective, namely, the knowledge of that which exists in the object. When this is not impossible, it must often happen that the opposite of any proposition contradicts the subjective conditions of thought only, but not the object itself, or, that both propositions contradict each other under a subjective condition, which is mistaken as objective, so that, as the condition is false, both may be false, without our being justified in inferring the truth of the one from the falseness of the other.