What is Positive Proof?

Legal Definition
Direct or affirmative proof; that which directly establishes the fact in question ; as opposed to negative proof, which establishes the fact by showing that its opposite is not or cannot be true. Niles v. Rhodes, 7 Mich. 378; Falkner v. Behr, 75 Ga. 674; Schrack v. McKnight, 84 Pa. 30.
-- Black's Law Dictionary