5. Further contradictions appear in Sigwart’s very peculiar and doubtful doctrine concerning the postulates, which he opposes to the axioms. The latter are to be regarded as certain on the ground of their real intellectual necessity; the former, not on the ground of purely intellectual motives, but on psychological motives of another kind, on the ground of practical needs. (_Logic_, 2nd ed. p. 412 seq.) The law of causality: e.g. is, according to him, not an axiom, but a mere postulate; we regard it as certain, since we find that without affirming it we should not be able to investigate nature. Sigwart, by this mode of accepting the law of causality, that is, affirming, out of mere good-will, that in nature under like conditions, the same results would constantly be forthcoming, manifestly takes it for granted without being conscious of its intellectual necessity. But, if all “taking-as-true” (Fürwahrhalten) is an act of judgment, this is quite incompatible with his views as to the nature of the judgment. Sigwart has here, as far as I can see, but one way of escape, i.e. to confess that he does not believe in what, as a postulate, he accepts as certain (as e.g. the law of causality); then, however, he will be hardly serious in hoping for it. 6. This point becomes still more doubtful on reflection upon what (2) has been previously discussed. The consciousness of a universal necessity of thought does not, according to Sigwart, belong to the postulates, but rather to the axioms. (Cf. 5.) But Sigwart could only with any plausibility exhibit the consciousness of this universal necessity of thinking as operating in the consciousness of one’s personal necessity of thinking by making use of the universal law of causation. But this causal law is itself merely a postulate; it is destitute of self-evidence. It is therefore obvious that the universal thought-necessity in the case of the axioms is also a postulate, and consequently they lose what, according to Sigwart, is their most essential distinction from the postulates. It may perhaps be in accordance with this that Sigwart calls the belief in the trustworthiness of “self-evidence” a postulate. But how the statement so interpreted, can be brought into harmony with the remaining parts of his doctrine I am at a loss to conceive.