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Alvin Plantinga – Against Materialism

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The debate over what consciousness is and how it interacts with the body is a debate in which both science and philosophy operate. Philosophers have generally referred to this debate as the mind-body problem. The two general views on how to confront this problem are materialism and dualism. “Materialism is the idea that human beings are material objects — brains, perhaps, or some part of the brain — without immaterial selves or souls” (Plantinga 3). Conversely, dualism is the view that human beings are comprised of an immaterial soul and a material body. Under this broad view, humans are not only their body; they are primarily a soul. Both of these views are metaphysical positions. If materialism is true then human beings are just one substance. If dualism is true then human beings are two substances – an immaterial substance and a material one. I will not be analyzing how these two substances are integrated in the human being. Some philosophers think that human beings are composites and not necessarily two substances. Analytic philosopher Alvin Plantinga puts forth two arguments against materialism in his essay. His argument strategy is to use the modal intuitions of possibility and impossibility in relation to the mind-body problem. I will argue that Plantinga is correct in his assessment of materialism and that his two arguments are valid and sound.

Plantinga’s first argument is called the replacement argument. He thinks is it possible for a person to exist when their body doesn’t. He does not argue that we can exist disembodied but rather he does argue that we could exist in a different body. If materialism is true, then I am a material object. I am most likely identical to my brain or some part of my body. It seems completely possible that I could exist while my body no longer exists. Plantinga says that if it is true that a person could still exist even when their body no longer exists, then that person and his body are not identical (4). This is true because of Leibniz’ Law, specifically the identity of indiscernibles. “This says that if A is strictly identical with B, then A and B have exactly the same properties” (Armstrong 3). If the modal properties are different, then those two things are not identical. In the case of me and my body, the modal properties are different. Plantinga imagines a situation where modern science has advanced so well that it can replace body parts extremely quickly. The process can replace all of his body parts. He also imagines that his old body is annihilated. All of this takes place while he is “reading the comic section of the newspaper” (Plantinga 5). Science says all the matter in our body is completely different from our old body some time ago. Plantinga thinks that accelerating the process seems possible regardless of cell assimilation (6). Cell assimilation is the time required for new cells to integrate into the body. Our bodies are constantly creating new cells and these cells assimilate through causal activities with other cells in the body. All that is required for this argument is the following (B standing for body): “It is possible that: the cells in B are replaced by other cells and the originals instantly annihilated while I continue to exist; and the replacement time for B and those cells is shorter than the assimilation time” (Plantinga 6).

Alvin Plantinga considers a few objections to his thought experiment. He responds to an objection from a “Star Trek” scenario where a person is beamed or teleported to a new location. The objector thinks that this thought experiment is analogous to Plantinga’s and thus it clearly shows that it’s possible that your body survives this type of replacement. Plantinga does not think that this thought experiment is analogous. His argument says that your old body is completely destroyed while the Star Trek thought experiment is just a disassembly and reassembly of your same body. Another objection says that persons are events, not necessarily a material substance. It is true that I am the same as my life – an event– in the actual world, but my life could have been different. There is no necessary identity with me and my life. It fails to get around the replacement argument (Plantinga 7-11). Plantinga’s argument does seem to be true. It does seem possible that I should exist in a different body while my former body is destroyed. As long as this is logically possible then materialism cannot be true since we are not necessarily identical to our body.

His second argument is also from a modal intuition but this time it is an argument from impossibility. The motivation behind offering this second argument is because some critics might not fully trust possibility intuitions. For this second argument he explains basic features of consciousness we all know to be true. All of us have first person experience of emotions. We all have desires and beliefs. All things being equal, we cannot be identical to anything that lacks these properties. The problem for materialism, and the main point of this argument, is consciousness itself. How can a material object have beliefs, desires, experiences of pain et cetera? (Plantinga 11-12). Plantinga cites Leibniz’ thought experiment on how this can be demonstrated. Leibniz asks us to imagine a machine that perceives, desires, and thinks. Imagine that this machine is the size of a mill – we can enter this machine. When we look into the machine, all we can see are parts that are causing these perceptions to happen. But the interaction of these mechanical parts does not show any content as to what the perception or belief is. This seems false because we know the content of our own minds. Therefore, Leibniz thinks that materialism cannot adequately explain the content of our minds (Plantinga 12). What are beliefs comprised of in a materialist perspective? The materialist would argue that these beliefs are events. These events are something that takes place in the neuron structure of your brain. These beliefs have propositional content. Plantinga jokingly uses the example that his “belief that naturalism is all the rage these days has as content the proposition Naturalism is all the rage these days (Plantinga 13). All beliefs must be able to express propositional content. This is problematic for materialism because, as Leibniz’ argument showed, neurons firing in the brain does not reveal any type of content. How can a set of neurons be related to a proposition? It seems impossible to see how material interactions could possess content of this sort. If they have no content they how can material beliefs be about anything? (Plantinga 15). One objection could be that computers have propositional knowledge. Computers are material objects that have wires, mother boards, and hard drives. We can store propositions on a computer such as “naturalism is all the rage these days” (Plantinga 16). Thus, the objection would show that material objects can contain content. But this does not follow since, in the example with the computer, the content has to be original and not derived from actual consciousness. We input the proposition into the computer; the computer does not think up the proposition on its own. Peter van Inwagen sees this as a difficulty for materialism. He thinks it is hard to account for beliefs and content under materialism but he also thinks that dualism is not better off. An immaterial substance interacting with a material substance is equally mysterious because we cannot have a mental image of an immaterial substance (Plantinga 17-18). Plantinga thinks that this is irrelevant because just because we cannot have a mental image of something does not mean it’s mysterious. We do not have mental images of numbers for example but it seems clear we can know what numbers are to some degree. We have an understanding of numbers. Peter makes the second point that materialist can at least have a representation of the interaction amongst the material parts while dualist cannot have one. Dualism implies the soul, which is a simple entity that is not comprised of parts (Plantinga 19-21). To ask for a representation of how the interaction takes place is to misunderstand the nature of the soul. It is to want a set of causes to explain the interaction. If the soul is a simple substance, then the interaction is direct. Plantinga concludes that consciousness is only mysterious when we think of it in materialist terms. He also concludes that his argument and rebuttals to objections show that a material thing cannot have beliefs or content (Plantinga 20-22).

Alvin Plantinga’s arguments are correct. It seems to me that both are valid and sound. The use of modal intuitions seems to be fair in his method of argumentation. I think it is clearly possible that I could exist while my body does not. This could be false in the actual world. Just because it is false in the actual world does not mean that it is false in all possible worlds. I can imagine a world in which it is true. The argument from impossibility seems to be even stronger than the first. It seems hard to see how a material object can be about something. Our brains are just neurons firing away that have no content of what the beliefs are. Both arguments against materialism are successful and show that dualism has more explanatory power over it.

I have shown both arguments Alvin Plantinga puts forth in his essay Against Materialism and have argued that they are both true. The importance of the mind-body debate is not only philosophical but also practical in how we view human beings. Questions of ontology effect how we think in all other branches of philosophy and life.

Works Cited

Armstrong, D. M. Universals: An Opinionated Introduction. Boulder: Westview, 1989. Print.

Plantinga, Alvin. “Against Materialism.” (n.d.): n. pag. Web. 21 Nov. 2014.   <>.


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