The doctrine of spiritualism runs contrary to that of materialism. Having discussed arguments for the former, we'll now consider three opposing arguments for the latter:

1. The method of science demands parsimony. We shouldn't needlessly multiply causes and principles. Yet spiritualists postulate the existence of two principles – irreducible realities. This alone creates a presumption against them. They do this because they believe that perceptible matter can't have the property of thought. But why? The essence of things lies beyond our grasp, and every day new mysteries are solved. Perhaps one day it will be shown experimentally that matter is in fact endowed with spontaneity and thought.

1. Our first response to this argument is that, as we've seen, our own theory involves no such dualism. Viewed from the outside, reality is material, while from the inside, it's spirit. But it's always one and the same reality. Besides, the idea that one day perceptible matter may be shown to think is far-fetched. We've already shown that the qualities constitutive of spirit are different than those of matter, and the absence of these conditions means the absence of thought. A being that isn't unified can think no more than a being that isn't identical. No experiment can yield an impossible finding.

2. […]