Tuesday, September 26, 2006

Modus Ponens and Modus Tolens in the Materialism/Dualism Debate

[These are some notes I offered to my Introduction to Philosophy class related to the dualism/materialism debate. What do you think of these arguments?]

Questions that Matter, 5th ed. quotes J.J. C. Smart to illustrate “The New Materialism,” which is not mechanistic, unlike the materialism of La Mettrie. Smart argues for materialism on the basis of animal evolution. He writes:

It may be asked why I should demand of a tenable philosophy of mind that it should be compatible with materialism, in the sense in which I have defined it. One reason is as follows. How could a nonphysical property or entity suddenly arise in the course of animal evolution? A change in a gene is a change in a complex molecule which causes a change in the biochemistry of the cell. This may lead to changes in the shape or organization of the developing embryo. But what sort of chemical process could lead to the springing of existence of something nonphysical? No enzyme can catalyze the production of a spook! (Miller/Jensen, Questions that Matter, 5th ed., p. 160-161).

This is Smart’s argument (SA):

1. If animal evolution is true (antecedent), then there can be no nonphysical properties in human beings (consequent).
2. Animal evolution is conceived as entirely physical.
3. Further, from the physical alone, the nonphysical cannot come. Causal principle.
4. Animal evolution is true. (Affirming the antecedent of (1).)
5. Therefore (a), there are can be no nonphysical properties in human beings.
6. Therefore (b), materialism is true.

This argument is valid and uses the modus ponens deductive argument form. If the premises are true and the form is valid, the conclusion must be true.

However, we can turn Smart’s argument on its head by rearranging it as a modus tolens argument (denying the consequent). Call this Against Smart’s Argument (ASA):

1. If animal evolution is true (antecedent), then there can be no nonphysical properties in human beings (consequent).
2. Animal evolution is conceived as entirely physical.
3. Further, from the physical alone, the nonphysical cannot come. Causal principle.
4. The mind is not identical to matter. See Descartes’ and others’ arguments to that effect. These arguments appeal to the law of identity (A=A) and other logical principles.
5. Therefore (a), there are nonphysical properties in human beings (denying the consequent of (1).)
6. Therefore (b), materialism is false.
7. Therefore (c), animal evolution is not true.

This argument is valid and uses the modus tolens argument form. If the premises are true and the form is valid, the conclusion must be true. Of course, since SA and ASA have contradictory conclusions, they cannot both be true (the law of noncontradiction: A cannot be non-A). In fact, only one of them can be true, since humans either possess nonphysical qualities or they do not. (That is, the statements are contradictories, not contraries.) So, the philosophical debate focuses on the truth value of both the antecedent and the consequent.


Kevin Winters said...

This will not be surprising to you, but what nonphysical properties do humans have? It seems that every indication of something supposedly non-physical is so tied to space and embodiment as to be unnecessary, superfluous.

Douglas Groothuis said...

Thought is not reducible to matter. Propositional thoughts are true or false; matter is not true or false, etc.

Kevin Winters said...

But what is thought? Is it the organization of propositions? If so, then how do those propositions come about or gain their meaning? In the end you must essentially include active embodied being as a ground upon which thought itself is possible. I could also raise the question of why we must understand "matter" in reductionistic terms (beyond that it is currently philosophical tradition to do so): our body certainly isn't mere matter.

Kevin Winters said...

As two illustrations of my thoughts, see here and here.

Kevin Winters said...

Forgive me for thinking out loud, but lately I've been trying to get a grasp of exactly what "thought" is meant to entail when it is used as you use it: what is thought? Can it really be described as immaterial, or as having no location or spatial context? Even mathematics, with all its abstractions, requires space: that terms are spatially related (they are written from "left" to "right," terms can be "trans"-itive, etc.), that they are symbolized (symbols are spatial in nature, as it is by their spatiality that we identify them), even that they require the discipline of mathematics with all its practical foundations (adding and subtracting objects, paying the rent, etc.). If we are to claim that thought is indeed immaterial, content needs to be given both to "thought" itself and what exactly "immateriality" adds (other than merely claiming that it is not the currently fashionable understanding of "matter," which, as a negative term, is really contentless).

Jim Pemberton said...

All forms of naturalism that I am aware of hold as a presupposition that materialism is true for the sake of scientific discovery. Therefore, we are told, naturalistic evolution is true. I believe you correctly parse the syllogism. The argumentation we are fed by the naturalists, therefore, is the fallacy of affirming the consequent.

John Stockwell said...

The fundamental problem with both of these arguments is that they are corrupted with imprecisely defined terms. These terms are are "materialism", "animal evolution" and "nonphysical properties".

Dr. Groothuis claims that "thoughts" are nonphysical, yet, surely he is aware of physical measurements of electrical brain
activity, and more recently proton emission tomograpy (PET) scans, which show areas of the brain metabolizing radiometrically tagged glucose. It does not appear that thoughts are separate from brain chemistry/electrical activity.
We have no reason to believe in today's world, that "thought is nonphysical".

As far as the term "materialism" is concerned, I believe that the word "physicalism" is a more modern usage. There are two problems with attempting to argue either from or against positions of physicalism.

First, we do not have complete understanding of all that is physical. If non-physical means "not in accordance with physical laws", then we have a problem that we don't know all of the physical laws, or under what conditions all of the ones we do know might/might not hold.

We do not have a hard physical understanding of all aspects of our observed world, including properties of human beings. Yet to use that fact to argue against physicalism may be simply be an argument from ignorance. (Indeed, the scientist *must* view this as the case, or abandon the scientific enterprise.)

Second, and more importantly, the epistemology of science is based on a notion of intelligibility and empiricisim.
Today the term "physical" simply means "what physical science studies". The term "non-physical" may not have any meaning at all, in the long haul.

Regarding the term "animal evolution", we are talking about a scientific theory. Our understanding of evolution today is different than it was 50 years ago, and we have every reason to expect that our understanding of biology will be different 50 years hence. So, what we call "animal evolution" today, may seem out of date and tacky in a few years, but not because evolution is disproven, but because what we call evolution is understood in a different light.

Kevin Winters said...


In relation to your post, I'm not only questioning the usefulness of an 'immaterial' entity, but I'm also denying that reductivistic 'physicalism'--understanding the human mode of being through the currently fashionable view of 'matter' (however outdated from physics' perspective; philosophy is always behind physics in these things)--is adequate. What is needed is a new vocabulary for describing our active embodiment that informs and makes possible our most abstract thought.

William Bradford said...

Your ASA argument is logically sound. I would add though that one could argue that there are nonphysical properties found in higher animals i.e. minds capable of feelings and some reasoning capacity albeit, obviously at a lesser level than humans. The emergent property argument leaves much to be desired.