a fortioriadverb
/ˌeɪ.fɔː.tiˈɔː.raɪ//ˌeɪ.fɔːr.t̬iˈɔːr.i/formalfor an even stronger reason:
The proposition is incomprehensible to us, and hence a fortiori we cannot be justified in believing it.
a fortiori
adjective /ˌeɪ.fɔː.tiˈɔː.raɪ//ˌeɪ.fɔːr.t̬iˈɔːr.i/
his a fortiori argument