  Le Grand’s account of body-body interaction clears the way to explain mind-body interaction. In the same way as finite bodies, God functions as the effective principle of finite minds, providing the ultimate source of change: “… there is nothing, besides motion, which can strike the organs of the senses, or affect the mind itself.” (1694, p. 284) Although mind and matter are substances sharing no common properties, it is in virtue of God acting as the effective principle that mind and body interact. This kind of interaction is no more or no less problematic than the interaction of two physical bodies. There was no real problem of interaction for Le Grand, since he believed that it was not the substances per se that acted on one another but in all cases God alone provided the motive force in the universe. Although things by their nature respond to this motive force in an orderly way, i.e., according to the laws of nature, the fact that they exist as they do and that they interact is a fact completely dependent on God’s will. God’s power is expressed as local motions in bodies and as passions/thoughts in minds. In short, it is in virtue of God, their effective principle, that a mind and body, or a body and body, or even a mind and mind, are said to interact.