On the Fourfold Root of the Principle of Sufficient...

We have still to record various fruitless attempts which have been made to prove the Principle of Sufficient Reason, mostly without clearly defining in which sense it was taken: Wolf's, for instance, in his Ontology, § 70, repeated by Baumgarten in his "Metaphysics," § 20. It is useless to repeat and refute it here, as it obviously rests on a verbal quibble. Plattner[52] and Jakob[53] have tried other proofs, in which, however, the circle is easily detected. I purpose dealing with those of Kant further on, as I have already said. Since I hope, in the course of this treatise, to point out the different laws of our cognitive faculties, of which the principle of sufficient reason is the common expression, it will result as a matter of course, that this principle cannot be proved, and that, on the contrary, Aristotle's remark:[54] λόγον ζητοῦσι ὧν οὐκ ἔστι λόγος. ἀποδείξεως γὰρ ἀρχὴ οὐκ ἀπόδειξίς ἐστι (rationem eorum quærant, quorum non est ratio: demonstrationis enim principium non est demonstratio) may be applied with equal propriety to all these proofs.

For every proof is a reference to something already recognised; and if we continue requiring a proof again for this something, whatever it be, we at last arrive at certain propositions which express the forms and laws, therefore the conditions, of all thought and of all knowledge, in the application of which consequently all thought and all knowledge consists: so that certainty is nothing but correspondence with those conditions, forms, and laws, therefore their own certainty cannot again be ascertained by means of other propositions. In the fifth chapter I mean to discuss the kind of truth which belongs to propositions such as these.

To seek a proof for the Principle of Sufficient Reason, is, moreover, an especially flagrant absurdity, which shows a want of reflection. Every proof is a demonstration of the reason for a judgment which has been pronounced, and which receives the predicate true in virtue precisely of that demonstration. This necessity for a reason is exactly what the Principle of Sufficient Reason expresses. Now if we require a proof of it, or, in other words, a demonstration of its reason, we thereby already assume it to be true, nay, we found our demand precisely upon that assumption, and thus we find ourselves involved in the circle of exacting a proof of our right to exact a proof.