All deduction is a priori.

One cannot deduce an elementary proposition from another. There is no way to infer the existence of a situation from the existence of another, entirely different situation. There is no causal nexus which would justify such an inference. We cannot infer future events from present events. Belief in a causal nexus is superstition.

Free will consists of not being able to know future actions now. We could only know them if causality were an internal necessity like that of logical inference: The connection between knowledge and what is known is that of logical necessity. ('A knows that p is the case', makes no sense if p is a tautology.) If the truth of a proposition does not follow from the fact that it is self-evident to us, then its self-evidence in no way justifies our belief in its truth.

If one proposition follows from another, then the latter says more than the former, and the former less than the latter.
• If p follows from q and q from p, then they are one and same proposition.
• A tautology follows from all propositions: it says nothing.
• Contradiction is that common factor of propositions which no proposition has in common with another.
• Tautology is the common factor of all propositions that have nothing in common with one another.
• Contradiction, one might say, vanishes outside all propositions: tautology vanishes inside them.
• Contradiction is the outer limit of propositions: tautology is the unsubstantial point at their centre.