  The epiphenomenalist wishes to preserve the integrity of physical science and the physical world, and appends those mental features that he cannot reduce. The parallelist preserves both realms intact, but denies all causal interaction between them. They run in harmony with each other, but not because their mutual influence keeps each other in line. That they should behave as if they were interacting would seem to be a bizarre coincidence. This is why parallelism has tended to be adopted only by those – like Leibniz – who believe in a pre-established harmony, set in place by God. The progression of thought can be seen as follows. Descartes believes in a more or less natural form of interaction between immaterial mind and material body. Malebranche thought that this was impossible naturally, and so required God to intervene specifically on each occasion on which interaction was required. Leibniz decided that God might as well set things up so that they always behaved as if they were interacting, without particular intervention being required. Outside such a theistic framework, the theory is incredible. Even within such a framework, one might well sympathise with Berkeley’s instinct that once genuine interaction is ruled out one is best advised to allow that God creates the physical world directly, within the mental realm itself, as a construct out of experience.