Full Idea
What makes logic a priori is the impossibility of illogical thought.
Gist of Idea
Logic is a priori because it is impossible to think illogically
Source
Ludwig Wittgenstein (Tractatus Logico-Philosophicus [1921], 5.4731)
Book Reference
Wittgenstein,Ludwig: 'Tractatus Logico-Philosophicus (Pears)', ed/tr. Pears,D. /McGuinness,B. [RKP 1961], p.47
A Reaction
That places the a priori aspect of it in us (in the epistemology), rather than in the necessity of the logic (the ontology), which is as Kripke says it should be.