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
Goran	-	Croatian, Serbian, Slovene, Macedonian
Theodoric	thee-AHD-ə-rik (English)	History
Chananyah	-	Biblical Hebrew
Theotleip	-	Ancient Germanic
Cathleen	kath-LEEN	Irish, English
Corrado	kor-RAH-do	Italian