This article elucidates arguments presented against substance dualism (or mind-body dualism) and several responses to those arguments. Here we view substance dualism to affirm the view that the mind and body are two distinct substances that can exist independently of each other.
Perhaps the most common argument against dualism, as articulated by philosopher Paul Churchland, is that mental states are dependent on the brain. According to Churchland,
“If there really is a distinct entity in which reasoning, emotion, and consciousness take place… then one would expect reason, emotion, and consciousness to be relatively invulnerable to direct control or pathology by manipulation or damage to the brain. But in fact the exact opposite is true” (1).
Philosopher Chad Meister offers the following explanation,
“[A]rguments have been offered to support the materialist view, and most of them hinge on the claim that a physical brain is necessary for a functioning mind. On one materialist view, called the identity theory, all mental properties are identical to physical properties of the brain. The mind just is the activity of the brain, and so there is no need to posit some additional immaterial mind or soul to account for reason, emotion, will, or consciousness. Much of the evidence in support of this view comes from the apparent neural dependence of mental phenomena. For example, narcotics, alcohol, and other drugs affect one’s mental abilities, as do various brain diseases. This makes sense if the mind is the activity of the brain, but not so, it is argued, if the mind is a separate immaterial substance… since drugs and brain diseases affect mental abilities and consciousness, this provides strong empirical evidence that brain activity and consciousness depend on the brain (or are identical to the workings of the brain). Similarly, brain damage also affects consciousness and mental capabilities. Beyond this, various mental abilities are locatable in the brain. For example, the prefrontal cortex is the area of the brain in which the operations of consciousness, thinking, learning, and imagination occur. Taken together, these facts offer strong support that for an individual human self to be conscious, he or she needs a live, physical brain. Since dead persons lack a live, physical brain, there cannot be conscious life after death” (2).
Churchland claims that this “comes close to being an outright refutation of (substance) dualism.” But property dualism (PD), however, is “not threatened by this argument, since, like materialism, PD reckons the brain as the seat of all mental activity.”
Dualists typically retort that just because there is a causal connection between brain states and mental states, it does not follow that mental states are identical to brain states. Identity theorists reply that there is no need to add an additional substance when the data can be explained with just one. Philosophers William Lane Craig and J. P. Moreland counter “that if a doctor touches part of one’s brain with an electrode, it may cause a certain mental experience, say a memory, to occur. But all this proves is that the mind is causally connected to the brain, not that they are identical” (3). Craig and Moreland continue,
“To establish physicalism, it is not enough that mental states and brain states are causally related or constantly conjoined with each other in an embodied person. Physicalism needs identity to make its case, and if something is true, or possibly true of a mental substance, property or event that is not true, or possibly true of a physical substance, property or event, physicalism is false” (4).
There is the so-called problem of embodiment. Here the critic of substance dualism asks: What is it for the mind to be housed in a body? What is it for a body to belong to a particular subject? The problem of embodiment, argues the critic, makes the union between mind and body mysterious.
There is the argument from the physical conception of human beings at the beginning of life. According to this objection, no one views fertilized ova as having minds; rather, these are purely physical entities. But if human beings began as wholly physical beings and nothing non-physical was later added, then they are still wholly physical creatures and substance dualism must be false.
Fourth, there is the problem of interaction. Interactionism on substance dualism maintains that the mind and body causally influence each other. But some philosophers argue that this causes problems: if, on substance dualism, the mental substance is so radically distinct from the physical substance (the mental is, unlike the physical, immaterial, unextended, and therefore has no size, shape, location, mass, motion, or solidity), then they lack commonality necessary for interaction. The question then that the substance dualist must answer is how the material and the immaterial impact each other? Further, if a mind can indeed interact and move bodies, then why can it move only one particular body and not others?
Critics counter that this objection assumes that if one does not know how A causes B, then it is not reasonable to believe that A causes B, especially if A and B are different. But this assumption is questioned as we often know that one thing causes another without having any idea of how causation takes place. For example, gravity can act on a planet millions of miles away and protons exert a repulsive force on each other even though we have no idea how such interactions take place. Despite us not knowing exactly how the mind and body interact, it remains that we are constantly aware of causation between them. According to Craig and Moreland, “Episodes in the body or brain (being stuck with a pin, having a head injury) can cause things in the soul (a feeling of pain, loss of memory), and the soul can cause things to happen in the body (worry can cause ulcers, one can freely and intentionally raise his arm). We have such overwhelming evidence that causal interaction takes place, that there is no sufficient reason to doubt it” (5).
Finally, there is the argument from evolution, in particular, that it is known that physicalism is a driving force behind evolutionary theory. Churchland puts it this way,
“The important point about the standard evolutionary story is that the human species and all of its features are the wholly physical outcome of a purely physical process… If this is the correct account of our origins, then there seems neither need, nor room, to fit any nonphysical substances or properties into our theoretical account of ourselves. We are creatures of matter. And we should learn to live with that fact” (6).
Churchland’s argument can be stated as follows:
P1. If humans are merely the result of naturalistic, evolutionary processes, then physicalism is true
P2. Humans are merely the result of naturalistic, evolutionary processes.
C. Therefore, physicalism is true.
Critics will object to P1. Some theists, for instance, will reject evolutionary theory because they believe it supports physicalism and naturalism. Other theists will agree with evolutionary theory but contend that it does not necessarily entail the truth of physicalism. They recognize that it does not follow that the truth of evolutionary theory (an empirical biological theory) implies the truth of physicalism (a philosophical ontology). To assume the truth of physicalism begs the question.
Further, objections could be raised concerning P2. The critic argues that humans are not merely the result of naturalistic, evolutionary processes. Although humans are a product of evolution it could be the case, for example, that God implanted consciousness or the soul into human beings or their ancestors at some point within the evolutionary process.
References
1. Churchland, Paul. 1988. Matter and Consciousness: A Contemporary Introduction to the Philosophy of Mind. Massachusetts: MIT Press. p.20.
2. Meister, Chad. 2009. Introducing Philosophy of Religion. Abingdon: Routledge. p. 193-194.
3. Craig, William Lane., Moreland, J. P. 2009. Philosophical Foundations for a Christian Worldview. Westmont: InterVarsity Press. p. 233.
4. Craig, William Lane., Moreland, J. P. 2009. Ibid. p. 233.
5. Craig, William Lane., Moreland, J. P. 2009. Ibid. p. 243.
6. Churchland, Paul. 1988. Ibid. p. 21.
Bishop's Encyclopedia of Religion, Society and Philosophy 
in Paul Churchland’s views, she speaks of the “physical” brain.
What does ‘physical” mean in the way she uses it?
Please note, I’m NOT asking about “physical” in the phenomenological sense – the “physical” things we touch and see all around us. As is common with physicalists, Mr. Churchland conflates the phenomenological meaning of “physical” with the strict usage of “physical” by physicists.
Churchland appears to believe that what is “physical” – AS DEFINED BY PHYSICISTS – is the basis not only of consciousness AND the brain, but of the entire universe.
What does he – or you, if you believe the same – mean by “physical” in the sense of the substratum of the universe?
Apologies if I sound overly “challenging” in the previous comment (just re-read it). I just came across your blog and initially assumed you were a confirmed physicalist.
Let this be a lesson to me – when writing to someone on the net about whom you know very little (even when writing to a self proclaimed physicalist) don’t make any assumptions, be kind, and be dialogic.
Ok, note to self: “Remember this, Don!”