Sentence:  It was a grand sentence of Emanuel Swedenborg, which would alone indicate the greatness of that man's perception, — "It is no <WSD>proof</WSD> of a man's understanding to be able to confirm whatever he pleases; but to be able to discern that what is true is true, and that what is false is false, this is the mark and character of intelligence." 
Meaning of the word marked with <WSD> tags:  The degree of evidence which convinces the mind of any truth or fact, and produces belief; a test by facts or arguments which induce, or tend to induce, certainty of the judgment; conclusive evidence; demonstration.