know whereof one speaks

to know well the subject that one is speaking about. You are wrong! You do not know whereof you speak. He simply doesn't know whereof he speaks.

Name	Pronounced	Usage
Elroy	EL-roi	English
Dietlinde	deet-LIN-də	German
Marin	-	French, Romanian, Croatian, Serbian, Bulgarian, Macedonian
Netanyahu	-	Biblical Hebrew
Justus	YUWS-tuws (German), JUS-təs (English)	German, Dutch, Late Roman
Hassan	['ha:sən]