Wiktionary
know one's own mind
alt. (context idiomatic English) To clearly understand one's own feelings, intentions, preferences, etc; to know precisely what one wants; to be decisive or determined. vb. (context idiomatic English) To clearly understand one's own feelings, intentions, preferences, etc; to know precisely what one wants; to be decisive or determined.
Usage examples of "know one's own mind".
But if one could know one's own mind, would that extend to the spirit?