a priori, a posteriori
A PRIORI and A POSTERIORI are taken directly from Latin (that's why you don't have an accent above the "a") and very formal and somewhat stuffy. Most French speakers would prefer the native "en principe" or "en théorie" and "après" or "avec du recul".
Also, "A"/"AB" (Latin) means "from, away from, by (eg 'written by…')" and is not cognate with French «à» anyways, which comes from Latin "AD," which means "to, towards."
I'd think that lawyers, philosophers and maybe mathematicians would be the exceptions.