What is the relation between soul and body, mind and matter?
That is the ontological question, with which the question regarding the origin of ideas and the certainty of knowledge, or the critical problem, is closely allied. What is the relation between the soul and God, – between human liberty, on the one hand, and divine omnipotence, on the other? That is the moral question, which is closely connected with the preceding. In order to solve the former, reasoning and experience must be reconciled. If we consult the facts only, sensation is evidently the body’s action upon the soul, the action of matter on mind. And evidently, voluntary movement is the action of the mind on the body. We are acted upon by matter, and react upon it. Hence a relation, a very intimate relation, obtains between the two substances. But when they compare the results of observation with the dualistic metaphysics of the master, the Cartesians become involved in insoluble difficulties, and are confronted by mysteries on every side. The mind is a thinking substance and witho
