other hand, the principles that govern thinking are unconditioned laws and are able to be seen only by “ideation” or from pure concepts. They are not subject to the limiting condition, “if . . .” The principle of contradiction is intrinsically valid, and its validity is independent of how many people or what kind of people accept and enact it. It does not mean that the validities of two contradictions are incompatible so long as all individual minds think according to the same law, but the reverse. If thinking is to be lawful, it must be subject to this rule that is founded on the absolute state of mutual incompatibility between contradictory propositions and propositional meanings. The validity of the principle of contradiction is not and cannot be affected by the mental organization of human beings, because this very principle implies nothing about such organization. What can and do change are mental capacities for understanding, and the degree of the mental possibility of comprehension, and the degree of depth in understanding.²³

δ) So we finally see that even the kind of certitude with which we understand and embrace the empirical laws of psychology and the ideal laws governing meaning and propositional content is different. Apprehending ideal laws is characterized by apodictic insight: the laws are absolutely free of doubt. The certitude of our knowledge of empirical laws is propositional: it yields only a de facto and probable “it’s-this-way-and-not-otherwise.” Apodictic certainty yields an unequivocal, absolute “cannot-be-otherwise.”

But that lets us immediately see the fundamental error that psychologism lives off. It tries to establish something about the ideal being and ideal relations of valid statements by means of knowledge of empirical events in the mind, i.e., in temporally changing reality. As regards certitude, all knowledge of empirical facts has only the mark of probability. By their very nature and claim, the principles of thought, however, [49] are valid not for this or that case nor, as it were, for a while, but unconditionally and absolutely. Therefore the probable knowledge of facts can decide nothing about the unconditioned relations of validity. Likewise, the certitude of propositional knowledge of facts is inadequate for the vision that accompanies absolutely valid propositions: apodictic certitude.

Basic laws of thought, which do not intend empirical facts, cannot be corroborated or refuted by such empirical facts. For all its explanations, for all its claims to have the laws of thought for its subject matter, psychologism never operates in the arena where alone those judgments are made.

23. [The German Ursprünglichkeit here means “closeness to the origin” rather than “originality”; hence, “depth.”]