The Many Fallacies of Dualism

Published on October 3, 2026 10:32 AM GMT This is a linkpost for The Many Fallacies of Dualism by Brian Tomasik, which was published in fall 2013, and last updated on 10 November 2017. Below are the summary, introduction, core argument against dualism, and summary of what various concepts refer to under physicalism. Summary Many seeming puzzles in philosophy stem from platonism and dualism. These fundamental illusions are like Capgras syndrome in that they persist in spite of no rational justification. They play central roles in confusions about consciousness, spiritual realms, free will, moral realism, and mathematical truth. Physicalist monism [physicalism] dissolves these conundrums by postulating that there is just physics, and what we think of as platonic forms are merely concepts—"clusters in thingspace"—that our material minds use to categorize and predict physical processes. Introduction We naturally have dualist intuitions in many domains: Dualism on consciousness: Yes, we have neurons and synapses, but it feels like there must be "something more" to my subjective experience than matter moving around. Spiritualism: Yes, the world operates according to physics, but there must be some additional spiritual force that animates it and gives it meaning. Libertarian free will: Yes, either my actions are determined or else random, but it feels like there's some extra "agency" property that I have that somehow gives me libertarian free will. Moral realism: Yes, I don't like slavery, but there has to be something more—some eternal "truth" of the matter as to how slavery is objectively wrong. Mathematical platonism: Yes, these sets and numbers that I'm manipulating are useful for predictions and organizing thoughts, but there must be some additional sense in which they "exist" in a platonic realm of perfect mathematical forms. There are many flavors of dualism, and I won't explore the intricacies here, but what I mean by the term is this sense that "there must be something more than mere physical stuff." What's wrong with dualism? The core argument The fundamental problem with dualism is that it doesn't accomplish anything except to complicate our theories. There are two possibilities. The first possibility is that the additional substance influences physical events—so-called interactionist dualism. In this case, the substance is not really extra-physical; it's just a different part of physics. The fact that both quarks and gluons exist is not dualism—these are just two types of physical substance. If there were some further, more mysterious force that also affected physical processes, we would say that it was part of physics too. If your dualism invokes a force that affects physics, I wouldn't call that dualism. Let's agree to call it physicalist monism and move on. The only other possibility is that the additional substance doesn't influence physical events. In this case, what is it supposed to accomplish? Why do I need an entirely separate non-physical thing if it doesn't contribute any extra explanation in the theory? This is called the "interaction problem." You might say that the extra substance explains why we have a sensation of "something more" than physical operations, but that's not right, because your verbal statements that "there's something more" are happening within physics, and if the extra stuff isn't affecting them, then physics by itself accounts for why you feel there's something more. But if physics itself explains why you feel there's something more, then nothing is added by assuming there is something more. That hypothesis is totally useless and amounts to "multiplying entities beyond necessity." Physicalist monism In summary, we have a thorough reduction of ontology [context] to just one level of reality—physical stuff. What is a table? It's a category into which we classify physical objects that tend to have legs, on which people tend to eat dinner, and that are often made of wood or metal. What is "green"? It labels a cluster of the appearance of certain objects, such as summer leaves, grass, and Christmas trees. Empirically it corresponds to light at about 510 nm in wavelength. What is consciousness? It's a category into which we classify physical operations by minds when they aggregate, broadcast, and manipulate information in certain ways. What is free will? It's a sensation we feel when choosing. It reflects a recognition that our decision procedure has multiple options that it's evaluating and for which different activations in the brain are being generated. What is truth? Our brains have epistemological systems that classify some statements as "true" and others as "false." We have additional machinery that allows us to manipulate these statements (using logic) in ways such that, when we act upon the statements expressed by the manipulated versions (deduced conclusions), we tend to achieve successful predictions of observed outcomes. Because of the utility of these systems,