Dualism, as used by Dr. Barr, is the belief that the soul and body exist separately. The phrase that has been used to lampoon this belief is, "the ghost in the machine." How our mental and spiritual faculties interact with our bodies is not well understood, but our ability to comprehend science and theology depend on it. This of course begs the issue of 'free will' and why we can understand the world around us. Reductionists, those that say we are just complex physical reactions with no meaning, have trouble accounting for our ability to comprehend.The Catechism of the Catholic Church, for example, rejects it (dualism) explicitly: “The unity of soul and body is so profound that one has to consider the soul to be the ‘form’ of the body.… Spirit and matter, in man, are not two natures united, but rather their union forms a single nature.” Barr, Stephen M.. Modern Physics and Ancient Faith (p. 173). University of Notre Dame Press. Kindle Edition.
Determinists ( are those who think there is no free will) those that maintain that we are nothing but atoms, cells, organs and physicial interactions, must rely on something that escapes their physicalist explanation to do science at all. Again, quoting Barr,The great mathematician and scientist Hermann Weyl, reflecting upon the implications of quantum theory in 1931, made the following observations, which remain valid today:
"We may say that there exists a world, causally closed and determined by precise laws, but … the new insight which modern [quantum] physics affords … opens several ways of reconciling personal freedom with natural law. It would be premature, however, to propose a definite and complete solution of the problem. One of the great differences between the scientist and the impatient philosopher is that the scientist bides his time. We must await the further development of science, perhaps for centuries, perhaps for thousands of years, before we can design a true and detailed picture of the interwoven texture of Matter, Life, and Soul. But the old classical determinism of Hobbes and Laplace need not oppress us longer." Barr, Stephen M.. Modern Physics and Ancient Faith (p. 184). University of Notre Dame Press. Kindle Edition.
"However, we do not have to infer the existence of our minds. We experience them directly in the process of using them. We do not infer the existence of our minds, rather we infer the existence of everything else with our minds. To put it another way: the brain does not infer the existence of the mind, the mind infers the existence of the brain. We may doubt our inferences about external things, but it is madness to doubt the reality of the mind itself and the reality of its basic powers." Barr, Stephen M.. Modern Physics and Ancient Faith (p. 188). University of Notre Dame Press. Kindle Edition.
If these few quotes sound intriguing, you might enjoy this book. This review is a little disjointed, but I can't even offer a comprehensive explanation of how my soul and body interact. I just know that they do. This book is also available on Audible.com, although you might want the physical copy also to review some of the more intriguing points. I hope these samplings from Dr. Barr's book are helpful.