 Reichenbach considers, and rejects, the subjective interpretation of probability advocated by the then prominent philosopher and psychologist Carl Stumpf (1892a, b), and, less emphatically, the attempt at an objective interpretation advocated by Johannes von Kries (1886), a physiologist who had studied with Hermann von Helmholtz. According to Reichenbach, von Kries’s account of probability needs to be freed from the principle of insufficient reason—that mutually exclusive events of which we have no knowledge that would determine differential probability are equally probable. As a subjective principle, Reichenbach claimed, it had no place in science. Reichenbach insists on an “objective” interpretation of probability—in the Kantian sense as about the world of experience—for which probability statements are synthetic, but not verifiable, claims about the empirical world. His task, as he sees it, is to demonstrate that probabilistic statements are supported by a claim—the “existence of a probability function”—which is a transcendental principle that is necessary, and in combination with causal principles sufficient, for empirical knowledge. 