Plantinga's Dualism and the Mind-Body Problem

The following blog summarizes Christian philosopher Alvin Plantinga’s reconstruction of the argument for Cartesian dualism in Meditation II.27 of the Meditations on First Philosophy. The original argument establishes a modal premise that Plantinga uses in order to reformulate the argument for dualism. Neither argument is impressive. Ultimately, Plantinga offers two distinct modal arguments in favor of dualism. My blog defends two claims: my first thesis is that the traditional problem of interactive dualism (originally raised by Princess Elisabeth of Bohemia) is not as problematic as usually made out. Rather, the more serious problem is that the traditional theory violates the principle of the causal closure (henceforth CC) of the physical domain. Philosopher of mind Jaegwon Kim argues from the principle of the explanatory sufficiency of physics and CC to the explanatory exclusion (henceforth EE) of the mental. In the interests both of allowing for the possibility of a successful neuroscience and cogntive science and in order to avoid over-empowering the agent with miraculous power, my second proposal is that the interactive dualist should accept the thesis of overdetermination.

I

René Descartes argues that the mind or soul is substantial yet distinct from the physical body (Descartes, Meditation II.27).[1] Plantinga reconstructs the argument from the text in the following manner:[2]

(1) Possibly, I exist and there are no material objects.

However, if (1) is true, then

(2) I am not a material object.

At best this argument is excessively vague. One could likewise argue from

(1') Possibly, I exist and no brothers-in-law exist.

to

(2') I am not a brother-in-law.

From (1) it only follows that (2) is possibly true, but it does not follow that (2) is in fact true. Hence:

(3) Possibly, I am not a material object.

The argument at best establishes that it’s a contingent truth that human beings are in fact physical objects. Plantinga points out, however, that something else of interest follows from the conjunction of (1) and (1'). “It follows that there are worlds in which I exist and not only am not a body, but do not have a body. Being embodied, therefore, is not essential to human persons.”[3] However, someone might object that

(4) All human persons have bodies.

is necessarily true. Maybe, maybe not, but “in neither case does it follow that human persons are essentially embodied. What follows is only that, if they are not, then being a human person is not essential to human persons, just as being a brother in law is not essential to brothers in law. The property of being a human person (as opposed to that of being a divine person or an angelic person or a person simpliciter) may entail the possession of a body; it may be that whatever, in a given world, has the property of being a human person has a body in that world. It does not follow that Socrates, who is in fact a human person, has the property of having a body in every world he graces. As it stands, therefore, Descartes’ argument does not establish that he is not a body or a material object.”[4]

Plantinga fills in some of the gaps. He runs his argument in the first person. Imagine first that I’m an object made of matter. The natural thing to conclude is that if I’m identical with an object made of matter, then I'm identical with my "body" (B). But

(5) It is possible that I exist at a time when (B) does not exist.

It seems broadly logically possible that I should acquire a new body either by: a) exchanging bodies with someone else as in the case of the prince and the cobbler[5]; or b) gradual replacement of (B) piece by piece by another body or all at once.[6] The replacement could even involve some synthetic material. In these cases, then, it is clearly possible that I acquire a new body and continue to exist when (B) is destroyed. Thus

(6) There is a time t at which it is possible that I acquire a new body (B’) and continue to exist when (B) is destroyed.

“Accordingly there is a time t at which it is possible that I exist and (B) does not …. Hence I have the property "exists at t in W"; (B) lacks that property.”[7] The contrapositive of Leibniz's law of the indiscernibility of identicals provides a test for nonidentity or difference. If there is one thing true of x that is not true of y or vice verse, then x is not identical to y. Therefore, it follows that I am not identical with (B). “But then surely there is no material object at all with which I am identical …. Given (1) or (1') or (5), what Descartes' argument establishes is that human persons are essentially immaterial."[8]

Having summarized Plantinga’s formulations and reformulation of the Cartesian argument for dualism, consider now the contemporary appraisal of the mind-body problem and the two most common objections to interactive dualism.

II

A brief review is in order. On the one hand, mental states appear to be sui generis and unanalyzable in physical terms. However, on the other hand, mental and physical states appear to interact causally, nomologically, and explanatorily. The mind-body problem, says Barry Loewer, refers to the tension which arises in affirming each of the following three principles:

(7) Mental events and properties are not reducible to or explicable in terms of physical events and properties.(Dualism)

(8) Mental events and properties are involved in causal explanations of other mental events and physical events.(Interactionism)

(9) The physical is causally and explanatorily closed.[9] (Principles of CC and EE)

Historically, many philosophers have been dualistic interactionists – have affirmed (7) and (8) – holding that mental and physical states causally interact with each other (Plato and Descartes are probably the two most famous examples). It appears, however, that classical dualism or substance dualism is incompatible with (9). Thus, “A more serious problem [for interactive dualism] is that as the physical sciences advanced the following version of principle (9) became increasingly plausible

(9') To the extent that a physical event (i.e the change in the value of a physical property) can be causally explained, it can be to that extent causally explained by reference only to other physical events.

However, (9’) contradicts (7) and (8). If the most complete causal explanation of a physical event makes reference only to other physical events, and if mental events are distinct from physical events, then, contrary to (8), they cannot be causes of physical events.”[10] Kim offers some support for 9’): Descartes held that, “in spite of their separateness and independence,” the mental and physical domains “are causally connected: mental events can be, and sometimes are, causes and effects of physical events, and changes in a mind can be causes or effects of changes in a body. This means that events of both kinds can occur as links in the same causal chain: if you pick a physical event and trace its causal ancestry or posterity, you may run into mental events, and similarly if you start off with a mental event. It follows then that under Cartesian causal dualism there can be no complete physical theory of physical phenomena. For it allows physical occurrences that cannot be causally explained by invoking physical antecedents and laws alone. Any comprehensive theory of the physical world must, on Cartesian interactionism, include references to non-physical causal agents and laws governing their behaviour. We can say then that Cartesian interactionism violates the causal closure of the physical domain.”[11] The prevailing idea is that a natural and scientific account of mind which satisfies our intuitions about causal interaction requires a physicalist account of mind. Reductive physicalists, then, reject (7) and affirm (8) & (9).

Most philosophers of mind are probably not substance dualists today for two reasons: A) the general problem of interactive dualism; and B) the argument from causal closure and explanatory exclusion. Consider first the general problem of interactive dualism.

The Cartesian thesis of interactive dualism prompts Elisabeth's question: "So I ask you please to tell me how the soul of a human being can determine bodily spirits, in order to bring about voluntary actions?”[12] “Descartes, whose writings shaped our current understanding of the mind/body problem, argued that since he could clearly and distinctly conceive of his mind existing without body and body without mind, these are different and separable substances. He claimed that mental substance is essentially thinking and non-extended while physical substance is essentially extended and non-thinking. By ‘thinking’ Descartes referred to a process which is both essentially conscious and intentional. He rejected principle (9) and believed that certain behavior – specifically linguistic and mathematical behaviour which exhibit a certain creativity – cannot be accounted for causally entirely in terms of physical events.”[13] The problem for Descartes "is that within his framework it is difficult to understand how mental events and physical events causally interact since in his mechanistic physics causation is by contact. Descartes' well-known attempt at a solution is that mind and body are joined in the pineal gland. At best this localizes the problem rather than solves it since it fails to explain how non-extended substance can be in contact with extended substance"[14]

Plantinga’s response is direct: such arguments do not affect the interactive dualist who is also a theist. The theist already knows of at least one immaterial thing that can cause change in the physical world, namely God. Thus, the argument against Cartesian interactive dualism from the general problem of interaction is unsound. However, Harry G. Frankfurt has formulated an argument that requires attention.[15] If the mind causes physical changes, changes for which the causal laws of physics are causally insufficient to explain, then, for each act of which is caused by the mind, it would be a vulgar display of miraculous power. Furthermore, such acts are far too common to be miraculous. Frankfurt’s basic worry is that Plantinga’s position gives the agent the kind of ability people generally think belongs only to God. Thus, while Plantinga’s response successfully counters the general problem of interactive dualism, it does so only at the expense of making our actions not only mysterious but also miraculous. For this reason, it appears that the real controversy with interactive dualism is not the general problem of interaction, but the more specific problem of violating the principle of the CC of the physical domain.

Next, consider the charge that Cartesian dualism violates the principle of the CC of the physical domain. Jaegwon Kim formulates his argument from EE based on the principle of CC.

Most contemporary psychologists are reductionists about mental properties. They take mental phenomena to be psychological states which are in fact equivalent to brain states. Think of the reduction of various concepts in the special sciences: temperature to mean kinetic energy (Rumford’s ‘kinetic’ theory of heat which is anticipated by Sir Isaac Newton’s Opticks Query 18), of light to electromagnetic radiation, or of water to H2O. The idea is that the reductive enterprise should be adopted in response to the mind-body problem given its apparent success in the special sciences.

In support of the reductionist thesis, that mental phenomenon is ultimately reducible to and identifiable with states of the brain, many physicalists advance a form of the EE principle advanced by Kim.[16] Kim’s argument is briefly analyzed, and it appears to present a false dilemma against the interactive dualist, because there are other logical alternatives. My proposal is that the interactive dualist could accept the thesis of overdetermination and effectively neutralize the argument from EE. Thus, the proponent of overdetermination may consistently accept (7)-(9).

Kim’s explanatory exclusion argument presupposes two principles: A) the principle of the CC of the physical domain; and B) the EE principle.

Causal Closure Principle: If at time t a physical event has a cause, it has a sufficient cause at time t that is physical (9).

The Exclusion Principle: If an event has two or more sufficient causes at one time, then it’s a case of overdetermination (9).

Kim states further, “Most philosophers, including anyone who considers himself or herself a physicalist of any kind, accepts physical causal closure.”[17] With Kim’s two principles in hand, the argument against interactive dualism may be formulated in the following manner:

(10) M is a sufficient cause of P. (Interactionism/Type D causation)

(11) P* is a sufficient cause of P. (Principle of CC and EE.)

(12) M ≠ P*. (Dualism)

(13) This is not overdetermination.

M is symbolic for the mind or soul, and P* and P are symbols for physical events. According to dualism P has two causes. P is caused both by M and P*. If M had not occurred, then P would have occurred. If P* had not occurred, then P would have occurred. In this way P is overdetermined by M and P*. By (11), says Kim, the EE principle kicks in and requires that we must eliminate either M or P* as a sufficient cause of P. Kim concludes:

(14) “P* stays, M must go.”[18]

Kim believes the argument poses the following dilemma: accept either epiphenomenalism or the identity thesis. On Kim’s evaluation of the argument, there are two alternatives: A) deny (10) and eliminate genuine mental causation (epiphenomenalism); or B) deny (12) and identify M with P* (identity thesis). Kim suggests following strategy B) and advances his version of the identity thesis in order to preserve mental causation.

However, if there are independent reasons in support of dualism, such as Plantinga’s mind swapping and replacement arguments, then which aforementioned premise should the dualist deny? My contention is that the explanatory exclusion argument confronts the interactive dualist with a false dilemma. Kim argues that we should reduce mental states to brain states and accept the identity thesis. However, in so doing he simply ignores the interactive dualist who accepts the thesis of overdetermination.[19] My suggestion, then, is that the dualist should deny premise (13). Kim offers no reason to think that overdetermination is something that must be avoided.

Consider the following examples of overdetermination:

Overdetermination 1: Two assassins fire their rifles at the same time and both hit the target. Each bullet is a sufficient cause of death. Each would have killed the target had the other not fired.

Overdetermination 2: A two story building has many support beams in its infrastructure. Removing one beam will not cause the building to fall down. The building’s standing is overdetermined by the multiple support beams.

These cases involve overdetermination. There is no good reason to suspect that the overdetermination of the physical by the physical is not possible because it is common place.

Overdetermination 3: An invisible Genie lifts up the carpet in sync with Alladin’s lifting of the carpet. In this case, the carpet’s being lifted or rising is overdetermined by multiple causes (both material and immaterial).

Overdetermination 4: An invisible Genie stands on a rock. In this case, the rock’s immobility and position is overdetermined by the physical laws (i.e. gravity) and the efforts of the invisible Genie.

If this is accurate, then why should we find the overdetermination thesis of interactive dualism any less possible, particularly when we find that such an understanding is presupposed by our common place use of folk psychological predicates (i.e. believing, desiring, wanting. etc.) in the explanation of behavior? Not on the basis of Kim’s argument from CC and EE. Overdetermination is a conceptually coherent thesis to which the interactive dualist may avail herself. Furthermore, the most telling objection to overdetermination, that of the large type wide scale systematic coincidence of mental and physical events (we don’t expect to look for two gunmen upon each firing), is plausibly neutralized given the theistic hypothesis of a Leibnizian pre-established harmony which permits of Type D or downward causation. This solution is easier to swallow given Plantinga’s theistic response to the general problem of interactive dualism. If we buy into a theistic solution in that case, then why not appeal to theism in this case as well? The theist is none the worse off, and substance dualism emerges unscathed.

III

In conclusion, it appears that the traditional problem of interactive dualism is not as problematic as usually made out. Rather, the more serious problem is the violation of the CC of the physical domain entailed by traditional Cartesian interactive dualism. In the interests of allowing for the possibility of a successful neuroscience and cognitive science and in order to avoid over-empowering the agent with miraculous power, my second proposal is that the interactive dualist should accept the thesis of overdetermination.

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[1] Descartes, René “Meditations on First Philosophy” The Philosophical Writings of Descartes Volume II of Vol. I-II translated by John Cottingham, Robert Stoothoff, and Dugald Murdoch (New York, NY: Cambridge University Press, 1985, 18^th printing 2006), p. 18.

[2] Plantinga, Alvin The Nature of Necessity (Oxford, London: Oxford University Press, 1974), pp. 65-69.

[3] Plantinga, Ibid., p. 67.

[4] Plantinga, Ibid., p. 67.

[5] Locke, John An Essay Concerning Human Understanding (Amherst, NY: Prometheus Books, 1995), pp. 250-251.

[6] For a counter-response to Plantinga’s replacement version of the argument, see Van Inwagen, Peter “Plantinga’s Replacement Argument” Alvin Plantinga edited by Deane-Peter Baker (New York, NY: Cambridge University Press, 2007), pp. 188-202.

[7] Plantinga, Ibid., pp. 67-68.

[8] Plantinga, Ibid., pp. 68-69. Plantinga also considers Von Wright’s defense of the argument. In the interests of simplicity and space, however, this part of Plantinga’s assessment is not included.

[9] Loewer, Barry “Mind/Body Problem” A Companion to Metaphysics edited by Jaegwon Kim and Ernest Sosa (Malden, MA: Blackwell Publishing, 1995), p. 328.

[10] Loewer, Ibid., pp. 328-329.

[11] Kim, Jaegwon “The Non-Reductivist’s Troubles with Mental Causation” Mental Causation edited by John Heil and Alfred Mele (Oxford, NY: Oxford University Press, 1993, reprinted 2003), pp. 189-190.

[12] Elisabeth von der Pfalz “Elisabeth to Descartes” The Correspondence p. 62.

[13] Loewer, Barry Ibid., p 328.

[14] Loewer, Ibid., p. 328.

[15] Frankfurt, Harry G. “Freedom of the Will and the Concept of a Person” The Journal of Philosophy, Vol. 68, No. 1 (Journal of Philosophy Inc., Jan. 14, 1971), p. 18.

[16] Kim, Jaegwon Philosophy of Mind 2^nd ed. (Cambridge, MA: Westview Press, 2006), p. 195.

[17] Kim Ibid., p. 195.

[18] Kim Ibid., p. 197.

[19] For a defense of the thesis of interactive dualism see Mills, Eugene “Interactionism and Overdetermination,” American Philosophical Quarterly, Vol. 33, No. 1 (University of Illinois Press on behalf of North American Philosophical Publications, Jan., 1996), pp. 105-117.