#788 How Can an Immaterial God Act in the Physical World?

Dr. craig’s response

I deal with your very question, Abbie, in the first volume of my projected Systematic Philosophical Theology in the section on “Divine Incorporeality.” Obviously I can’t repeat here everything that I say there, but let me hit a few highlights.

Your question is probably the major philosophical objection to anthropological dualism raised by physicalists, known as the Causal Interaction Problem. Although physicalists use the objection to argue against the reality of the soul or mind, it obviously has a theological application as well.

In their forthcoming book on mind/ body dualism Moreland and Rickbaugh distinguish two ways to interpret the Causal Interaction Problem.[1] On the one hand, it may be taken to be a demand for some sort of mechanism between mental and physical entities in virtue of which they interact with one another. This demand is, however, inept, since the effect of the mind upon the body, on pain of embarking on an infinite regress, is taken by dualist-interactionists to be immediate, without any intervening causal linkage.

On the other hand, if the question is taken as simply an expression of scepticism that there could be such immediate causal connections, then the force of the objection can be easily exaggerated. Let me make several points.

1. The physicalist critic is somewhat hard-pressed to provide evidence that the only causal relations possible are among physical objects. After all, souls, in contrast to causally effete abstract objects like numbers, are concrete entities endowed with causal mental powers sufficient for effects like thoughts. Why not powers to affect the physical realm as well? The materialist cannot simply charge that evidence is completely lacking for mental/physical interaction, for to all appearances, it seems that the mental and physical do interact.[2]

We may not agree with William Hasker that the problem of causal interaction “may well hold the all-time record for overrated objections to major philosophical positions,” but its force should not be exaggerated.[3] Hasker is not alone in pointing out that one reason it is not decisive is that “all causal relationships involving physical bodies are at bottom conceptually opaque. We have no ultimate insight into the causal relations involved except to say, ‘That’s the way things are.’”

2. Perhaps the most powerful response to this objection by anthropological dualists is that we have good positive reasons to think that the soul is an immaterial substance that causally affects the body, even if we do not understand how. Moreland and Rickabaugh point out that dualist entities like conscious states and the soul are not only entities of which we have direct acquaintance, but entities whose reality is supported by philosophical arguments from the unity of consciousness, the possibility of disembodied survival or body switches, the best view of an agent in support of libertarian agent causation, the metaphysical implications of the use of the indexical “I,” and the special sort of diachronic and synchronic unity of human persons.[4]

Similarly, in considering physicalist objections to divine incorporeality, we must not forget that we have sound theistic arguments that support divine incorporeality. Arguments such as the kalām cosmological argument, the teleological argument from the fine-tuning of the universe, and the argument from the uncanny applicability of mathematics in physics provide powerful reasons for thinking that there is a transcendent Mind who has created the universe. These arguments provide a strong cumulative case in support of divine incorporeality that may well outweigh the objections brought against the doctrine. In particular, they outweigh expressions of incredulity based on our ignorance of how the mental affects the physical.

3. As if this were not enough, it seems to me that the dualist-interactionist can turn the tables and argue cogently that the materialist claim that causal interaction is impossible is incapable of rational affirmation. I have reference here to Alvin Plantinga’s celebrated Evolutionary Argument against Naturalism (EAAN). We can formulate Plantinga’s argument as follows:[5]

As Hasker perceptively recognized, EAAN is not so much an argument against naturalism as an argument against materialism.[6] Indeed, what Plantinga’s argument is really about is the so-called Causal Closure of the Physical (CCP). As defined by philosopher of mind Jaegwon Kim, “This is the assumption that if we trace the causal ancestry of a physical event, we need never go outside the physical domain.”[7] The closure principle requires that all physical events have only physical causes. If there do exist immaterial entities, they are irrelevant because of the causal closure of the physical domain. Materialists may embrace or deny the reality of mental states of awareness, but they all deny their causal efficacy in the material world. Plantinga’s argument is therefore best cast as the Evolutionary Argument against the Causal Closure of the Physical (EAACCP).

Plantinga’s argument is thus directly relevant to the present objection based on the impossibility of causal interaction between the soul and body. If EAACCP is sound, then the materialist’s claim cannot be rationally affirmed and collapses in self-defeat. Hasker wryly comments, “To say that this constitutes a serious problem for physicalism seems an understatement.”[8]

Is EAACCP successful? I can’t go into the question here, but suffice it to say that on the basis of Andrew Moon’s trenchant analysis of the argument,[9] I am persuaded that Plantinga’s argument is successful. If this is right, then the most widespread and influential philosophical objection to substance dualism and, hence, to divine incorporeality cannot be rationally affirmed.

In summary, there is no evidence for the causal closure of the physical, and physical causation is ultimately just as inexplicable as mental causation. Given the sound arguments for a transcendent Creator and Designer of the universe, we can be confident that God can interact causally with the physical world, even if we do not understand how, just as, given our direct acquaintance with ourselves and the arguments for the existence of the soul, the dualist-interactionist can be confident that the soul does interact causally with the body, even if we do not understand how. Finally, the impossibility of causal interaction between soul and body and, hence, between God and the world cannot be rationally affirmed, since to affirm the causal closure of the physical is irrational.