Although the real interaction of body and mind be denied, some explanation must, at least, be given for the appearance of interaction, _i.e._ for the actual correspondence of bodily and mental phenomena. Occasionalism denotes the theory of occasional causes. It is not the body that gives rise to perception, nor the mind that causes the motion of the limbs which it has determined upon--neither the one nor the other can receive influence from its fellow or exercise influence upon it; but it is God who, "on the occasion" of the physical motion (of the air and nerves); produces the sensation (of sound), and, "at the instance" of the determination of the will, produces the movement of the arms. The systematic development and marked influence of this theory, which had already been more or less clearly announced by the Cartesians Cordemoy and De la Forge,[1] was due to the talented Arnold Geulincx (1624-69), who was born at Antwerp, taught in Lyons (1646-58) and Leyden, and became a convert to Calvinism. It ultimately gained over the majority of the numerous adherents of the Cartesian philosophy in the Dutch universities,--Renery (died 1639) and Regius (van Roy; _Fundamenta Physicae_, 1646; _Philosophia Naturalis_, 1661) in Utrecht; further, Balthasar Bekker (1634-98; _The World Bewitched_, 1690), the brave opponent of the belief in angels and devils, of magic, and of prosecution for witchcraft,--in the clerical orders in France and, finally, in Germany. [Footnote 1: Gerauld de Cordemoy, a Parisian advocate (died 1684, _Dissertations Philosophiques_, 1666), communicated his occasionalistic views orally to his friends as early as 1658 (cf. L. Stein in the _Archiv für Geschichte der Philosophie_, vol. i., 1888, p. 56). Louis de la Forge, a physician of Saumur, _Tractatus de Mente Humana_, 1666, previously published in French; cf. Seyfarth, Gotha, 1887. But the logician, Johann Clauberg, professor in Duisburg (1622-65; _Opera_, edited by Schalbruch, 1691), is, according to the investigations of Herm. Müller _(J. Clauberg und seine Stellung im Cartesianismus_, Jena, 1891), to be stricken from the list of thinkers who prepared the way for occasionalism, since in his discussion of the anthropological problem (_corporis et animae conjunctio_) he merely develops the Cartesian position, and does not go beyond it. He employs the expression _occasio_, it is true, but not in the sense of the occasionalists. According to Clauberg the bodily phenomenon becomes the stimulus or "occasion" (not for God, but) for the soul to produce from itself the corresponding mental phenomenon.]