(_a_) _Occasionalism._ Occasionalism has appeared in the history of Philosophy as a professed solution of the special problem of the apparent interaction between body and mind, taken as two entirely disparate and independent realities, though it is equally applicable in a wider sense to the more general problem of the apparent connection of any two independent real things. The doctrine is most closely associated with the names of the Cartesians, Arnold Geulincx and N. Malebranche, but was in part also adopted by Berkeley as a consequence of his belief in the pure passivity of non-mental things. Starting from the Cartesian conception of mind and body as two entirely independent and disparate kinds of reality, Geulincx and Malebranche were confronted by the apparent fact that mental states lead to modifications of bodily state in voluntary motion, and _vice versâ_, bodily states determine the occurrence of mental states whenever a sensation follows upon a stimulus. The “natural view of the world” unhesitatingly accepts these cases as instances of interaction or Transeunt Causality on exactly the same level as the origination of change of state in one body by change in another, and Descartes himself had acquiesced in this interpretation. But such a view, as his successors saw, is quite incompatible with the alleged disparateness and independence of the two orders of existence, the bodily and the mental. Geulincx and Malebranche accordingly took refuge in the doctrine that the interaction is only apparent. In reality there is a complete solution of continuity wherever the series of changes in the one order terminates and that in the other begins. What really happens, they taught, is that God adapts the one series to the other. On the occurrence of the bodily stimulus, God intervenes to produce the sensation or emotion which is required to harmonise our action with our environment. Similarly, on the occurrence of a volition, God interferes to set the corresponding movement going in our bodily organism. Thus the change in the one order is merely an occasion for the intervention of God, who is the actual cause of the corresponding change in the other. Within each order the series of changes once initiated are then supposed to be causally connected. The divine interference only comes in where the two orders come into contact. Berkeley adopted half of this doctrine without the complementary half. Inasmuch as, according to him, physical or non-mental things are mere complexes of presentations, or, in his own terminology, “ideas,” and ideas are purely inert, the real cause of every sensation must be God, who thus directly intervenes to give us an indication of the further sensations we shall receive according to the action we take on the present presentation. Transeunt Causality in the reverse direction, the immediate origination of bodily movement by volition, Berkeley seems to have admitted without criticism as a self-evident fact.[113]