An argument has been made against Descartes interactive substance dualism theory that will be analyzed and evaluated in this paper. The Christian apologist J.P. Moreland argued in an online video that goes as such: “If interactive substance dualism is true, a non-physical substance could have an effect on a physical substance. It is metaphysically impossible that a non-physical substance could have an effect on a physical substance. Interactive substance dualism is false.” (Moreland J. P., 2009) This paper will set forth to point out that this argument against Descartes’ interactive substance dualism theory, while being valid in nature, is unsound because its second premise is false. With the help of modern science; this paper will argue that it is indeed metaphysically possible for a non-physical substance to have an effect on a physical substance.
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Before we can appropriately analyze and evaluate the argument, some terms must be defined first so that we may understand how this paper will defend interactive substance dualism. The first step when evaluating an argument is to look at the logic of the argument. According to Bruce Miller of the University of Michigan an argument is logically sound only “if the premises were true, this fact would constitute good grounds for accepting the conclusion as true” (Miller, 2000). The current argument against Descartes’ appears to follow logical correctness which leads to the next idea. Is the argument a deductively valid one? Miller also states that “an argument form is deductively valid if and only if it is impossible that its conclusion is false given its premises are true.” (Miller, 2000) If we were to assume that the premises of the argument in question were true then we would also be drawn to the same conclusion found in the argument. The second premise of the argument states that the first is untrue and therefor the conclusion is true. If the second premise were in fact true, then one could safely claim that interactive substance dualism is indeed false. This flow of sound logic structures and frames this as a deductively valid argument, but is it deductively sound?
Even though an argument can be structured logically and found to be deductively valid; that may not always make the argument sound. A sound argument can be summed up as an argument that is based on truths. If a conclusion or argument is drawn from false premises then the argument is considered unsound. For instance, if I were to say that all X are Y and all Y are Z, then I could safely conclude that all X are Z. Yet using a qualifier such as ‘all’ or ‘every’ can be tricky, because if just one Y is not Z, then not all X’s could be Z’s – making the statement deductively unsound. So now that we understand what deductively sound and unsound is, let us apply it to the argument at hand. To do this we will evaluate the premises and decide whether they are true or false.
The first premise of the argument at hand is a reiteration of Descartes’ interactive substance dualism theory that a non-physical substance could have an effect on a physical substance. “Substance dualism generally holds that the body is a physical object having physical properties and that the mind is a mental substance containing mental properties irreducible to the physical.” (Moreland & Craig, 2003) When one experiences pain for example, the body may incur certain electrical and chemical stimulus (physical properties), which results in the self or mind consciously experiencing the felt quality and awareness of the pain (mental property). Descartes argues within substance dualism that the mind and brain closely interact with each other, though they are different substances with differing properties. This is considered to be Descartes’ main point in the interactive substance dualism theory and this premise will be considered true.
The second premise is where this paper focuses because the argument claims that it is metaphysically impossible that a non-physical substance could have an effect on a physical substance. This premise is false because modern science has shown the effects a mind has over a body and vice versa. It appears fairly obvious to most that physical properties do not have the same features as mental properties. For example, we are unable to apply physical qualities like mass and spatial dimensions to mental events such as thoughts, feelings of pleasure and sensory experiences. (Moreland & Craig, 2003) As philosopher Keith Maslin summarizes, “physical occurrences do not just appear to be different from consciousness; they are utterly different, so utterly different in fact, that it is inconceivable how the physical could produce the mental.” (Maslin, 2001)
Yet in a published journal we find that Bruce Hinrichs pointed out that when a person reads a sentence, hears a speech, experiences an emotion, or thinks a thought, a cluster or network of brain cells fires in a certain pattern with particular intensity and timing. (Hinrichs, 2001) Similarly, it has been observed that when a part of one’s brain is touched with an electrode, it may cause a mental experience such as a memory to occur. (Moreland & Craig, 2003) This is evidence in itself that mental states (the mind) can be reduced to physical states (firing of electrodes/electricity); but this only demonstrates so much. While the mind is partly connected to the body, they are not identical. Therefore, the distinctiveness of mental and physical properties and states argues favorably of substance dualism; and the casual connection the mind and body share is evidence supporting Descartes’ interactive substance dualism theory.
The existence of secondary qualities also argues favorably for interactive substance dualism. Secondary qualities are said to consist of properties like color, taste, sounds, smells and textures, whereas primary qualities are properties that characterize matter such as weight, shape, size, solidity, and motion. (Moreland & Craig, 2003) Frank Jackson explains that a strictly physical and material world would arguably force us to deny it:
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“We sense the world as made up of coloured, materially continuous, macroscopic, stable objects; Science and, in particular, Physics, tells us that the material world is constituted of clouds of minute, colourless, highly-mobile particles… Science forces us to acknowledge that physical or material things are not coloured… This will enable us to conclude that sense-data are all mental, for they are coloured.” (Jackson, 1977)
Effort should be made to at least acknowledge the criticisms of interactive substance dualism and potentially defend against them. Some have pointed out a problem of interaction when it comes to substance dualism. This may be the leading criticism against Descartes’ theory. “How can the soul, lacking all physical dimensions, possibly affect, and be affected by, the extended body?” (Maslin, 2001) It does not appear that we reasonably explain how each separate substance could interact with the other. This argument though appears to be based on an appeal to our ignorance. It assumes that if we do not understand how X causes Z that it is not reasonable to believe the two can interact. Craig and Moreland wrote that a tack can be moved by a magnetic field, and gravity acts on a planet millions of miles away. (Moreland & Craig, 2003) The magnetic fields and gravitational forces have very different properties to the solid and spatially located entities they affect, and while we may not fully understand how such an interaction occurs, it nevertheless does – just as we recognize the interaction between mind and body.
An argument was made against Descartes’ interactive substance dualism theory that will be analyzed and evaluated in this paper. The paper set forth to point out that this argument against Descartes’ interactive substance dualism theory, while being valid in nature, is unsound because its second premise is false. We discussed that the argument, while logically framed and deductively valid, was inevitably false because of its second premise. The paper presented several arguments in favor of substance dualism by showing the distinctiveness of mental and physical properties and states; as well as the existence of secondary qualities. The paper also examined the main criticism of interactive substance dualism and the problem of interaction between mind and body. Given the above arguments for interactive substance dualism and the successfully countered criticism, it seems clear to me that it is indeed metaphysically possible for a non-physical substance to have an effect on a physical substance. If this paper has performed its purpose adequetly, then you as the reader can agree that the 2nd premise of the argument against Descartes is false. If a conclusion is drawn from a false premise then the argument becomes deductively unsound and should leave the interactive substance dualism theory in a very convincing position.
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