On the Fourfold Root of the Principle of Sufficient Reason

§ 30 Logical Truth

A judgment may have for its reason another judgment; in this case it has logical or formal truth. Whether it has material truth also, remains an open question and depends on whether the judgment on which it rests has material truth, or whether the series of judgments on which it is founded leads to a judgment which has material truth, or not. This founding of a judgment upon another judgment always originates in a comparison between them which takes place either directly, by mere conversion or contraposition, or by adding a third judgment, and then the truth of the judgment we are founding becomes evident through their mutual relation. This operation is the complete syllogism. It is brought about either by the opposition or by the subsumption of conceptions. As the syllogism, which is the founding of one judgment upon another by means of a third, never has to do with anything but judgments; and as judgments are only combinations of conceptions, and conceptions again are the exclusive object of our Reason: syllogizing has been rightly called Reason’s special function. The whole syllogistic science, in fact, is nothing but the sum-total of the rules for applying the principle of sufficient reason to the mutual relations of judgments; consequently it is the canon of logical truth.

Judgments, whose truth becomes evident through the four well-known laws of thinking, must likewise be regarded as based upon other judgments; for these four laws are themselves precisely judgments, from which follows the truth of those other judgments. For instance, the judgment: “A triangle is a space enclosed within three lines,” has for its last reason the Principle of Identity, that is to say, the thought expressed by that principle. The judgment, “No body is without extension,” has for its last reason the Principle of Contradiction. This again, “Every judgment is either true or untrue,” has for its last reason the Principle of the Excluded Middle; and finally, “No one can admit anything to be true without knowing why,” has for its last reason the Principle of Sufficient Reason of Knowing. In the general employment of our Reason, we do not, it is true, before admitting them to be true, reduce judgments which follow from the four laws of thinking to their last reasons, as premisses; for most men are even ignorant of the very existence of these abstract laws. The dependence of such judgments upon them, as their premisses, is however no more diminished by this, than the dependence of the first judgment upon the second, as its premiss, is diminished by the fact, that it is not at all necessary for the principle, “all bodies incline towards the centre of the earth,” to be present in the consciousness of any one who says, “this body will fall if its support is removed.” That in Logic, therefore, intrinsic truth should hitherto have been attributed to all judgments founded exclusively on the four laws of thinking: that is to say, that these judgments should have been pronounced directly true, and that this intrinsic logical truth should have been distinguished from extrinsic logical truth, as attributed to all judgments which have another judgment for their reason, I cannot approve. Every truth is the reference of a judgment to something outside of it, and the term intrinsic truth is a contradiction.