April Fools' Day or beginning of idiocy from first principles
I believe the answer is:
a priori
Can you help me to learn more?
(Other definitions for a priori that I've seen before include "Way of reasoning" , "'Derived by logic, without observed facts (1,6)'" , "Presupposed through reasoning" , "Deductive, from cause to effect - in Latin" , "From logic rather than experience" .)