All disagreements about what promotes the good life—human flourishing and the common good—depend on one’s answer to the question “What is it to be human?” The last two weeks I’ve argued we are a unity of soul and body. This week I’ll consider the second answer: “To be human is to be a purely physical thing—a human body.”  Here I’ll discuss four reasons people give in favor of this view, and over the next two weeks I’ll discuss two more reasons. I’ll also explain why I think these reasons fail–why Physicalism is not the right answer to the question.

Reason #1: An A Priori Commitment to Physicalism

If everything that exists must be physical, then it follows that human persons, as one type of thing that exists, must be (only) physical.

This is the a priori assumption adopted during the “Enlightenment.” Before that, going back to the time of Aristotle and Plato, substance dualism was the answer most often given to the question “What are we?”

However, this answer didn’t sit well with Enlightenment thinkers. They were committed to the idea that only the physical world exists. So they didn’t like immaterial things such as natures, essences or souls. They spilled much ink to show how such beliefs were “old-fashioned” and should be abandoned. And many believed them. In fact, their view won the day, so much so that we now name their era the “Enlightenment.” This was the time, so the story goes, that we woke up from our dream and realized, or were “enlightened,” that everything is physical.

I have previously blogged on three reasons Physicalism (or Materialism), as an overall worldview, is false. Instead of reiterating those arguments here, see my blog series “Three Reasons to Believe in Things You Can’t See.”

Therefore, since Physicalism fails as an overall approach, it is not an accurate a priori assumption on which to base the belief that we are nothing more than our bodies.

Reason #2: Physicalism is the most logical answer

The Physicalist often argues that you just need to look at the evidence, and follow where it logically leads, to understand we are purely physical. This is the only conclusion that a rational person should choose. 

But to say this the Physicalist must begin by smuggling in a number of non-physicalistic assumptions. This makes the view self-defeating: if it is true, it must be false. Only if it is false may it be true. Let me explain.

The Physicalist is constructing an argument with a number of premises, leading to the conclusion “Human persons are purely physical.” But let’s stop and think about what this entails.

1.     It entails that the Physicalist can have certain ideas in her mind that she focuses her attention on. These are called “propositions”—immaterial entities that are believed and can be either true or false. But brains cannot have immaterial things like propositions in them. They can only contain atoms that interact with one another according to the laws of chemistry and physics.

2.      She assumes she can focus her attention on these propositions—intentionality. But as I argued last week, intentionality makes no sense if everything is physical. So the Physicalist can’t even begin to make an argument, because arguments need propositions and intentionality, two immaterial things the Physicalist already says don’t exist.

3.     The Physicalist argues there are logical relations between the premises and conclusion of her argument for Physicalism. But here another flag must be thrown, for what in the world is a “logical relation” if everything is physical? Relations are by definition immaterial things that stand between or among the things they relate. Logic is a type of right ordering of these relations among propositions. So now we have four immaterial things in play as the Physicalist argues for physicalism: propositions, intentionality, relations and logical orderings!

4.     The Physicalist is assuming he can see these logical relations and choose the correct conclusion. Another flag flies! Acts of “choosing” (exercising volition—the ability to select this over that) can’t be physical, for everything physical is determined by the laws of chemistry and physics. Choosing assumes something immaterial is involved. (I’ve argued this in more detail in a previous post.)

5.     The Physicalist is arguing that all these things—these propositions, this intentionality, these relations and these logical connections—are not just floating “out there” but are somehow grounded in her so that it is “her” argument. But this assumes she is a unity at a time. As I argued last week, only Substance Dualism makes sense of being a unity at a time.

6.     The Physicalist first thinks about and argues for the first proposition, and then for the second, and so on, until he at last considers and argues the conclusion (of Physicalism) follows. But wait a moment—this assumes he is present at each stage of this thought process. He is assuming sameness through change. I also showed last week that a person can only persist through time if he is an immaterial substance.

Therefore, the only way the arguments for Physicalism can be true is if these six non-physicalistic assumptions are smuggled into the argument. But then Physicalism can’t be right. The only way it can be correct is if these assumptions are not smuggled in. But then the Physicalist can’t say he sees the premises (propositions) are related and logically lead to the conclusion, and as he has thought this through he has chosen to accept the conclusion of Physicalism.

Reason #3: Physicalism is simpler

A useful approach to solving problems is known as “Occham’s Razor” (or the “Principle of Parsimony”). It basically says that one should always choose the simplest explanation available to adequately explain a phenomenon. For instance, if I can’t find my wallet, I should first assume the simplest answer–I’ve misplaced it–rather than first assume someone broke into my home and stole it. 

Physicalists apply this principle by arguing that since physical explanations of a person are simpler and adequate, there is no need to make the explanation more complex by adding the idea of a second substance, or soul, to the equation.

I certainly agree that Occham’s Razor must be used in our reasoning. Yet the key word is “adequate.” If the simplest answer is not adequate, it is not the best answer. For instance, let’s say that in addition to not being able to find my wallet, I discover my wife’s purse is also missing. And we can’t find our cell phones. And she discovers her heirloom watch is not where she left it. At this point the “simpler” explanation that these things were misplaced becomes less and less plausible, and the more complex explanation that someone broke in and robbed us, becomes a better explanation of all the data.

In the same way, as more and more data comes to light suggesting we have an immaterial dimension (as discussed these past two weeks), the Physicalist’s explanation becomes less and less plausible, to the point of being far less reasonable than Substance Dualism.

Reason #4: How can minds and brains interact?

Many point to the “problem of interactionism” (sometimes known as “The Ghost in the Machine” argument) as good reason to dismiss Substance Dualism. The argument is that the mind and the brain (or the soul and the body) are such different types of things that there is no way to understand how they could interact. There is no way to understand how an immaterial thing, like a mind, could cause a physical change, such as a change in a brain state. Therefore, there cannot be both a soul and a body. We must be a body alone.

At least three things can be said in response. First, for the Theist this argument has little force, because we have independent reason to believe that God, an immaterial reality, has and does cause physical effects (such as the universe coming into existence and the reality of miracles). Therefore, we have good reasons to believe it is not impossible (or even improbable) that other immaterial things (minds) can also cause physical effects.

Second, this is much less of a problem for Thomistic Dualism (and one reason I and many others prefer this over Cartesian Dualism—see week one of this series for more details of this distinction). On Thomistic Dualism the soul and body are deeply intertwined, such that each needs the other to “be all it can be.” So interaction between the two is to be expected. The brain causes effects in the mind, and the mind causes effects in the brain.

On the Cartesian view, the soul and body are completely separate and only related to one another superficially, as water is to the glass it is in. On this view there really is “a ghost in a machine”—both body and soul run on their own and don’t need one other. 

So even if this is a problem for the Cartesian Dualist, there is another, preferable dualistic explanation the significantly reduces, if not eliminates, this objection. It is interesting that almost all critiques of substance dualism are critiques the Cartesian variety. This strikes me as the straw man fallacy (describing the view you oppose in its weakest form so that it is easy to argue against). 

Third, this objection makes the false assumption that unless we know how something works we cannot know that it works. In other words, unless we know how the soul and body relate, we cannot claim that the soul and body do relate. But this is clearly false. There are many things we know to be the case, yet we can’t explain how they are the case. Take astronomy, for example. We knew the moon revolved around the earth long before we understood gravity well enough to understand how this was possible. Currently in quantum physics we know that quarks have certain causal effects (assuming a Scientific Realist approach to quanta phenomena—I’ll unpack this a bit more next week), though we do not yet know how they have these effects.

Therefore the “problem of interaction” is not as strong an argument against Substance Dualism as some take it to be.

Conclusion

Two arguments remain in favor of Physicalism. One is the “Enlightenment” idea that only Science gives us truth, so the search for a physical explanation for all things must go on. The second argument is that we can have what we want in the halfway house of Property Dualism, rather than full-blown Substance Dualism. I’ll discuss and respond to these arguments over the next two weeks.

Until then, grace and peace.

For further reading I suggest Philosophical Foundations For A Christian Worldview by J.P. Moreland and William Lane Craig; Chapter 12: “The Mind-Body Problem”