pseudo-mathematical speculations. While Wundt praised Kant's critical work and his rejection of a "rational" psychology deduced from metaphysics, he argued against Kant's epistemology in his publication Was soll uns Kant nicht sein? (What Kant should we reject?) 1892 with regard to the forms of perception and presuppositions, as well as Kant's category theory and his position in the dispute on causal and teleological explanations. Gottfried Wilhelm Leibniz had a far greater and more constructive influence on Wundt's psychology, philosophy, epistemology and ethics. This can be gleaned from Wundt's Leibniz publication (1917) and from his central terms and principles, but has since received almost no attention. Wundt gave up his plans for a biography of Leibniz, but praised Leibniz's thinking on the two-hundredth anniversary of his death in 1916. He did, however, disagree with Leibniz's monadology as well as theories on the mathematisation of the world by removing the domain of the mind from this view. Leibniz developed a new concept of the soul through his discussion on substance and actuality, on dynamic spiritual change, and on the correspondence between body and soul (parallelism). Wundt secularised such guiding principles and reformulated important philosophical positions of Leibniz away from belief in God as the creator and belief in an immortal soul. Wundt gained important ideas and exploited them in an original way in his principles and methodology of empirical psychology: the principle of actuality, psychophysical parallelism, combination of causal and teleological analysis, apperception theory, the psychology of striving, i.e. volition and voluntary tendency, principles of epistemology and the perspectivism of thought. Wundt's differentiation between the "natural causality" of neurophysiology and the "mental causality" of psychology (the intellect), is a direct rendering from Leibniz's epistemology. Wundt devised the term psychophysical parallelism and meant thereby two fundamentally different ways of considering the postulated psychophysical unit, not just two views in the sense of Fechner's theory of identity. Wundt derived the co-ordinated consideration of natural causality and mental causality from Leibniz's differentiation between causality and teleology (principle of sufficient reason). The psychological and physiological statements exist in two categorically different reference systems; the main categories are to be emphasised in order to prevent category mistakes. With his epistemology of mental causality, he differed from contemporary authors who also advocated the position of parallelism. Wundt had developed the first genuine epistemology and methodology of empirical psychology. Wundt shaped the term apperception, introduced by Leibniz, into an