a1 University of California (Riverside).
In his essay “Logical Empiricism”, in the anthology Twentieth Century Philosophy, Professor Feigl writes: “All forms of empiricism agree in repudiating the existence of synthetic a priori knowledge.” 2 Schlick makes the same point even more forcibly: “The empiricism which I represent believes itself to be clear on the point that, as a matter of principle, all propositions are either synthetic a posteriori or tautologous; synthetic a priori propositions seem to it to be a logical impossibility.”3 The denial of synthetic a prioris is a major thesis of the logical empiricist position, being found in the writings of most of the leaders of the movement.4 The reason for its importance is fairly clear. It provides a formula on which the empiricists can base their critique of traditional philosophy. To use Ayer's phrase, denial of the synthetic a priori results in “the elimination of metaphysics”. The philosophical tradition to which the empiricists are opposed and whose “metaphysics” they wish to eliminate can be called, somewhat loosely, rationalism.
1 This paper was read before the Pacific Division of the American Philosophical Association at the University of Oregon on December 30, 1958. I wish to thank Paul Bredenberg and David Harrah for their very helpful criticisms of the manuscript.