Mental Cause

In several essays on the broad subject of free will I have said that there are three types of causation in our physical universe: micro-physical indeterminism, macro-physical determinism, and agent-volition, the last subjectively experienced as the willful exercise of one’s mind’s causal capacity, “mental cause”. I refer to what Aristotle called “efficient cause”, that is the immediate forerunner (or forerunners) of a particular event or outcome taken to mean “that which physically brings that particular event about.” Aristotle defined four types of causes, three of which could be said, sometimes, to have “mental” aspects. A simple example here, a fire in a fire-place, will serve to illustrate Aristotle’s distinctions.

1. The “material cause” of the fire is that out of which it could be made. Wood or paper might work. Water would not. There also has to be some oxygen (or other oxidizer) present and so on.

2. “Formal cause” has to do not with the fire’s material substrate but its shape. Not all arrangements of even qualified materials will successfully light. To make a nice fire place fire, the wood and paper have to be arranged in certain ways. Many but not all possible arrangements will serve.

3. “Efficient cause” is that which physically brings the fire about. It might be a lit match set to paper for example. When physics talks about causes, it is this they are talking about. Importantly, there can be chains of efficient causes. To set my wood pile alight with a match I must first strike the match and light it, then hold its flame under my paper kindling. That last step is commonly called also the “proximate cause” and it is mostly this that this essay is about.

4. Aristotle’s fourth cause, the “final cause” is the reason we have built and lit our fire. We want to get warm. Notice that this cause is only indirectly connected to our fire. Besides starting a fire we might get warm in other ways. We could do physical exercise or put on a coat. The entire set up of the fire from the material (wood and paper), its arrangement, to its ignition, are merely means to this end.

Under normal circumstances, we would always attribute “final cause”, to a desire, aim, or objective (purposeful intention) of the agent to get warm. If “mental cause” (of any sort) even exists, final causes would always, by definition, be mental. “Material causes” (that wood and paper in the presence of oxygen can burn) are not typically thought of as mental. Formal causes (the arrangement of the wood and paper in the fire place) might or might not be mental. The wood and paper in their pre-light configuration is not mental per-se, but the arrangement-design might or might not be. In the case of our fire place an agent is involved, but for example in a natural forest (arrangement of trees) ignited by lightening, it is not. As with formal cause, efficient cause might or might not involve mentality. In the case of our fire place, an agent lights the fire, but in the forest fire, lightening does the job.

Notice that from a third-party viewpoint, efficient (causal) agency remains always a physical object. What lights our fire place is a body with arms and hands that strike matches, and so on. There is no need to assume mental cause is real from an outside perspective. When we get to an inside perspective however the situation is quite different.


What we need is some justification for believing mental cause exists, that it belongs in our ontology and “is real” by virtue of being one of the causes (somewhere in the chain of efficient cause) of [some] physical event. When we observe what we take to be a minded agent (human or animal) we see that the physical effects they engender are always products of a body’s motion. No one disputes the physical connection between the body and the rest of the world. The issue comes down to “what moved the body”? The answer is muscles of course, nerves, and more nerves comprising some part of the brain. The question is, was there something that isn’t a nerve as such (though a nerve would be involved) but something quintessentially mental, perhaps a desire or something like that lying at the beginning of the chain of efficient-causes?

Most people would say that it “seems as though” this is the case. Physics says this seeming must be an illusion because it discovers only two kinds of causes in the universe, the indeterminate and the determinate. To be sure, discovered here means measured. Physics detects, with physical instruments, only two types of causes. Speculation about mental cause goes back as far as the earliest recorded philosophy, but physics has never been able to detect it!

If however there is no mental cause when we seem so strongly to sense that there is, all sorts of philosophical problems arise. Mental cause is not the same as free will, but free will entails mental cause. Physics of course denies free will is real But if I am not warranted in believing my agency can be a cause, at least of my own body’s motion, how am I warranted in believing anything? Belief itself (causal or not) is a quintessential mental phenomenon. If my causal capacity is an illusion why not also my agency, and why not anything I might happen to believe or desire?

We can be deluded about our beliefs being true, but it is difficult to believe we are deluded about having beliefs, and doubly so for desires. The debate isn’t usually about having (subjectively experiencing) beliefs, but rather about their being anything “over and above” brain states. If physics calls my very agency into question (not the illusion of it, but its being something more than brain states) what is it then that has beliefs and desires? Can “brains” be an answer? How do brains, qua brains, come to have beliefs and desires? Do the mechanisms of a clock know the time of day in the sense that a human knows it when she looks at the clock? To deny brain states beneath (the foundation) of our mental states would in this day be absurd. The issue is always ultimately the ontological status of what appears, the subjective, as a result of their presence, and what (if any) downward causal powers the appearance has.

These sorts of issues are but the tip of the iceberg. If mental cause (and so by extension free will) is an illusion then a radical skepticism about everything would seem to be warranted. At the same time, even skepticism, since we must be skeptical of our very agency, is not warranted either. There is a long literature here, but as John Searle put it (The Construction of Social Reality [1995]) nothing about the human experience nor all of human history makes any sense without presupposing free will.


I have given some answer to this above: because physics cannot measure it. It would seem unproblematic to take for granted that physics doesn’t cover everything; it is, as the matter is put, incomplete. But the problem is more subtle than that. The two types of causes that physics can measure (strictly speaking physics cannot measure quantum phenomena directly, but only when these interact with the macroscopic world) have qualities, characteristics, that mental causes lack. These qualities are what explain in the sense of “reveal the mechanism for” physical causation. There is no mathematics in physics, no observation or experiment that would suggest that anything other than prior-physics can be a cause in physics. Even not-directly-observable quantum phenomena are readily observed via these same qualities when they interact with the macroscopic world. Purportedly “mental causes”, by contrast, do not appear to share these qualities. As a result, they cannot be observed from a third party viewpoint, and so no path exists to an explanation of the mechanism of their effect on physics.

Rather than accepting that some mysterious sort of cause that cannot be observed must be real, physicists and most philosophers instead move to strike “mental cause” from the list of causal possibilities in our universe. This is a philosophical move, an induction based on evidence from the only sort of detection or measurement instruments, physical instruments, that exist. The anti-physicalist might respond by claiming that while physical instruments can not in principle measure mental cause, subjective consciousness, literally our phenomenal arena detects them, and this arena is, after all, also a part of the universe along with everything else.

At this point we are thrown back upon the brain which is indisputably physical. We know that the movement of my arm is preceded by nerve impulses in my arm and brain that are themselves indisputably physical. If at the top of this chain of efficient cause there was a mental event that set the chain in motion it behooves the proponent of mental cause to say how, that is by what mechanism, the mental event effects (that is trigger) the first indisputably physical (nerve) process in the chain?


According to Phil Dowe (Physical Causation [2000]) material cause is all about transferring some [physically] conserved quantity momentum, mass-energy, or electric charge. If one billiard ball strikes another momentum is transferred from one to the other. This results in two other observations important in this context. First physical cause is temporal. Causes precede their effects. The transfer of a conserved quantity cannot take place faster than the speed of light. Second, there is a reciprocal impact of the effect on the cause. If one billiard ball gains momentum, the other loses it.

Both of these qualities are absent from mental cause. In this context, distinctions made by Nicholas Rescher (“Free Will: A Philosophical Reappraisal” [2008]) will be helpful. Rescher is aware of the overall relation between consciousness (including mental cause) and brain states. He claims that there never can be any instance of mental cause without the simultaneous existence of some correlated brain state. If we look for a mental event that brings about a brain state, but isn’t itself associated simultaneously with some other brain state, we will never find it. “Mental causes”, in Rescher’s terms are not causes in Dowe’s physical sense.

Mental causes are not, in Rescher’s view, temporal. They are literally (metaphysically) simultaneous with their effect, some brain state. He distinguishes this sort of a temporal cause by calling it “initiation”. Initiation (often intentional but not necessarily so) need not evoke a neurological correlate ex nihilo. It need only slightly modify an existing state. From a third party viewpoint, that modified state would appear a perfectly natural evolution from its own prior state. Nothing would be found to suggest that anything non-physical was responsible for it.

This “a temporal initiation” is possible because in mental cause, no conserved quantity is transferred, and consequently there is no reciprocity. If I elect to pick up a rock and throw it at a window, I can feel the momentum transfer between my arm and the rock, and of course the throw is temporal. But the initiation of the event was simultaneous with the physical brain state that lies at the top of the physically [efficient] causal chain. The evidence that this is so is our experience that there is no reciprocal effect of my choice to initiate a rock-throw back on that initiator. Nothing about the initiation impacts back on the mental cause itself. Of course I may, this being a directed (intentional) initiation, immediately regret having done so. But that is a different, subsequent, thought, not a modification of the original one.

If Rescher is correct about initiation, how can we tell if the choice (mental cause) results (simultaneity being granted) in a correlated brain state or the other way around? We cannot tell based on any physical measurement. Physicalists would say there is no reason not to suppose that the physical is logically (if not temporally) prior. But if Rescher is correct, what then of the mechanism problem?

With regard to mechanism, many speculations seem to orbit about some interaction at the quantum level. The a temporal nature of initiation coupled with a lack of conserved quantity transfer and so lack of reciprocity, are suggestive of quantum entanglement where, on some views (see Ruth Kastner “Understanding our Unseen Reality” [2015]), the same qualities (or lack of them) characterize quantum phenomena. Since we cannot measure quantum phenomena directly, as far as we know, prior to some manifestation in the macro world (the exchange of a conserved quantity) the same qualities as characterize “mental cause” (initiation) might characterize “quantum cause”. The most detailed speculation with regard to mind might be Henry Stapp’s (“Quantum Theory and Free Will [2017]) Quantum Zeno Effect (QZE), mind’s ability to hold or otherwise modify subtle quantum indeterminacy within the anatomical and physiological processes of the brain. True, even QZE does not say exactly how this power of the mental connects up to the physical, but in this case, neither side of the transaction can be directly measured and there are reasons to believe (see the aforementioned Kastner book) that quantum phenomena are also initiations in Rescher’s sense.


Above I have looked at mental cause from the physical side. What does it look like from the mental side? Some philosophers have characterized mental cause in terms of beliefs or desires. But beliefs and desires are not mental causes in Aristotle’s efficient sense. They are Aristotelian “final causes” and clearly mental, but not our issue here.  Being a reason is of course mental, but not all of what is mental is also causal. I might want to get warm (my reason for lighting a fire) but not move a muscle to do anything about it. The quintessential efficient mental cause is a volitional act, an exercise of will on the part of a minded agent. In our experience, only mind, the subjective consciousness of an individual, has this ability to act volitionally, for a purpose, and not either indeterminate or determined by prior physics.

Purposeful cause is mental and only mental, and it is causal, that is itself determining of subsequent physics, for example my throwing a rock. As much as I disagree with Schopenhauer, I do believe he was correct in locating will and representation at the core of phenomenal experience, or as we would put these in more modern terms, intention and qualia. Mental cause, in particular our capacity to control intent and by extension a body, is an intrinsic component of our “what is it like to be…” experience.

Qualia are the mental effects of physical (brains) causes (an over simplification but for purposes of this essay I leave it at that, see “From What Comes Mind”). Intention is a mental cause (initiation) of a physical effect. Throwing a rock begins with an intention, but this is also true for subjective states that exhibit no gross physical effects. Suppose on a nature walk you come upon a beautiful flower. You attend to it, visually, perhaps also aromatically at the same time. Suddenly you become aware of a buzzing sound from behind or above your head somewhere. You cannot see what is causing the sound, but without moving your gaze from the flower you have become aware of it. Becoming aware is clearly a mental event which in this case may be comfortably attributed to prior physics (brain states, bearing in mind Rescher’s initiation can work in both directions). Only subsequently do we volitionally attend to the sound, perhaps to identify it. The volitional element entails agent purposeful-direction and so mental cause even if no muscle has moved.

Under normal circumstances, when we are conscious, we are never without both qualia and intention about something. Is it possible one can be conscious without intention, qualia, or both? Advanced Buddhist monks, masters at meditation, claim to achieve the first, but even this being so, they maintain this special state only while meditating. Sensory deprivation might suggest the possibility of a qualia-free consciousness, but people report made-up qualia, images and sounds brains generate (and to which we attend as we do in a dream state) in the absence of external stimulation. Perhaps we cannot be conscious in the absence of qualia.


Mental cause is necessary but not sufficient for free will. In addition, free will demands agency, a subject whose will it is. An exercise of free willed choice is a volitional act of an agent. It is not either prior-determined, though often influenced, by physics, nor random. It is mental cause directed by agent-purposeful volition, itself quintessentially mental and unique to minded-agency in the universe. To get free will, mental cause must be real, and also subjective agency. The action of the body-agent of a physical event (throwing the rock) is willful only by extension from the [presumptive] mental-agent who is the initiator of that act. A body can sometimes act in the absence of agent consciousness. Such acts are not willful, and typically we do not claim that they are.

The connection between intention (willfulness) and subjective agency is built-in to human language. To speak of intention always implies subjective agency. So free will and mental cause are doubly linked. Free will rests on mental cause, but if free will is not real, there is nothing interesting left for mental cause to do. It is possible there are, for example, subconscious mental causes of which we are not aware (conscious of) and so not willed as such. But if in fact free will (not to mention agency as such) can be subsumed by brain states, there is no reason why subconscious mental cause could not be also.

An exercise of will (volition) by an agent is the quintessential “mental cause”. If free will is an illusion it is hard to understand the point of working to save mental cause. If all of our choices, our behaviors (including purely subjective sorts like “attending to”), are prior-determined by our brains what is left for mental cause to do? When Sean Carroll denies the possibility of free will because “If free will were real it would mean that mind causes physics” (The Big Picture [2016]) he is aiming, really, at mental cause. Free will goes along for the ride because it is the volitional exercise of the causal potential of mind that matters.

Agent volition then, and not beliefs or desires, is the epitome of mental cause. But if volition itself is prior-determined by brain states, and not a non-material (mental) agent, then there is no point to mental cause, the brain can do it all. In turn, mental cause, apart from the free will issue, is usually defended (or challenged) with reference to free will. The possibility of free will is grounded on the reality of mental cause and in addition the reality of the volitional agent able to utilize it. Both of these, in turn, rest on the reality of mind with the “power to cause physics”.

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