  What could be explained, according to Desgabets, is the way in which the mind and body are united and dependent upon one another. He found an analogue in the nature of the body-body relation: two bodies are united when their superficies touch and their movements take on a mutual dependence. Similarly, two minds are united when their thoughts and wills agree and depend on one another. The union of mind and body is not by touch, nor by agreement of thoughts, but by the dependence that exists between certain thoughts and certain movements such that one in fact follows from the other. The union of the mind and body in man is so strict that it founds a species of communication for their commerce, in virtue of which our thoughts are said to have duration, succession, etc., without themselves being corporeal. The union and its interaction cannot be further reduced in explanation. In short, the essence of man, who is composed of mind and body, is the union of mind and body, and the only legitimate questions which concern this union relate to how, given the union, the mind determines the body and the body determines the mind, which is an empirical question, known through experience not reason.