A priori knowledge ‘derived from the function of reason without reference to sense experience’ (Angeles, 1992, p. 159) does not depend upon sensual perception. For example, the knowledge Any triangle has 1801 or Any polygon with n nodes has (n2)*1801 can be derived without empirical experience, that is a priori. Angeles (1992, p. 159) spells out three
consequences: ‘The truth of a priori knowledge (a) is not derived from sense experience, (b) cannot be checked against sense experience, and (c) cannot be refuted by any sense experience.’