There is an old story of the net and the fishermen. A net having a weave that lets any object smaller than 10 inches long slip through it. Fishermen cast the net in the lake and harvest fish always ten inches long or longer. The fishermen mistakenly conclude that there are no fish in the lake smaller than 10 inches. Philosophy 101 students easily recognize the fishermen’s mistake. If there were fish in the lake smaller than 10 inches they would slip through the net.

Now imagine that there is some constraint on these fishermen that prevents them from weaving nets any more finely than they have. Is there any other means by which they might acquire evidence of fish smaller than ten inches long? As it happens there is. They can take some of the larger fish, keep them alive in captivity, and mate them. If successful, they would see that fish lay eggs, eggs hatch into little fish, and little fish, properly fed, grow into fish ten or more inches long! Having done this sort of thing many times, our fishermen can correctly induct, from many particular observations, that there are indeed fish in the lake smaller than ten inches because those smaller fish are the descendants of the bigger fish and one day will become bigger fish themselves.

Although the analogy is imperfect, physics, that is the present state of our body of science, has something in common with that net. Our senses and all the instruments and physics we can derive from them are physical. No matter how refined we make our instruments they are physical things and cannot measure or detect anything that isn’t also a physical thing. Quantum mechanics doesn’t help here. Ruth Kastner (“The Transactional Interpretation of Quantum Mechanics”) goes so far as to conclude that the solution to various quantum puzzles is to locate quantum phenomena outside of spacetime. But they remain very much physical nevertheless. As indeterminate quantum phenomena emerge into spacetime they become deterministic, fully participating in the time-bound causal web, subject to causal closure.

No one, even died-in-the-wool physicalists, deny that there is any logical proof of the absence of anything real that isn’t physical, but nevertheless most commit themselves to the proposition that no non-physical entity can be real based on the capacity of physics to be self-explanatory. There are also those who simply define ‘reality’ in such a way as to preclude anything that isn’t physical from being real, and therefore chalk up anything historically adduced for such reality to utter illusion, a mirage.

As with the problem of the net, we ask if there is any possible evidence for there being something real in the universe that isn’t physical? Unlike with the fish, we cannot merely encompass some part of the physical and watch it to see if it produces something non-physical. We can try of course. Experiments and observations have been going on since Newton, some would say since Galileo, without such a transformation ever being witnessed. Scientists and philosophers have long conceded that the non-physical, should it exist, cannot in principle be detected and measured with physical instruments, the only kind we can build. They further concede that it is, technically, an inductive error to conclude there is nothing other than the physical in the universe based on this incapacity alone.

What warrants that further conclusion is the observation that physics is causally closed on itself. It is one thing to concede that we could not in principle measure anything non-physical. But when we measure that which is physical, we discover that these measurements alone fulfill all explanatory requirements for the present state-of-the-universe. Physical causes and nothing but physical causes result in all the effects we can measure throughout the cosmos. Physical causes result only in physical effects and physical effects spring from nothing more than physical causes.

For my purposes, as with physics, ‘reality’ is associated with causal efficacy in the physical. Anything that is or can become a cause in the physical is real. Cause is to be taken to mean “contributing cause”. It need not be the sole cause, nor the physically proximate cause. To be a cause it is only required that some physical effect is the ultimate result. The causal closure hypothesis is related to the observation that physical effects have, at least, physical proximate causes. All measurable physical effects seem to have, immediate antecedents that are also physical. But this does not preclude the existence of non-physical causes. For a non-physical cause to be real, it is only necessary that an observer be able to connect up a purported cause and an effect measurable in the world. I will have more to say about this “connecting up”.

Among modern philosophers there are some (Chalmer’s, Nagel, Lowe, Haskers, Foster, O’Connor, and others) who push back on the physicalist claim. They argue that there is reason to believe that there is something both real and non-physical in the universe, specifically consciousness, that is a subjective through which we experience anything at all including our observation of the physical. Physicalists rejoin that this phenomenon, consciousness, is not a “non-material reality”. It is merely a way of viewing the material itself. A rain cloud looks very different from above and below, but both views are merely different perspectives of the same single thing. We confirm this assertion by tracing, physically, from the top to the bottom of the cloud and determine that it is the same entity viewed two different ways.

This does not appear to be possible as concerns consciousness. No physics has ever traced, physically, all the way from subjective experience to the physics (technically biology — brain states) that purportedly underlies it. Many (mostly scientists) argue that we just haven’t got there yet and we will someday make that tracing. Others, many more of them philosophers, argue that the physicalist rejoinder is more hubris than reality. That it might turn out impossible, in principle, to ever make that mapping. Of course this doesn’t mean brain states have nothing to do with consciousness for obviously they do. What it means is that consciousness is not (or may not be) merely “another view” of brain states.

I am not going to address those arguments here but I am going to explore the question whether or not this phenomenon we call consciousness is in fact evidence and in what way it is evidence for the existence of something real that is beyond the reach of physics because it is non-physical.

For any evidence to be evidence, the phenomenon for which it is adduced has to be real. There cannot be evidence for anything that is by definition unreal. At the same time any evidence, if it is evidence of anything at all, has to emerge from, or become available to, our subjective experience as observers. The evidence must appear in consciousness. From our own subjective points of view there is no evidence of anything in the universe, physical or otherwise, that doesn’t emerge in or through our experience — aided or unaided by instruments or quintessentially mental formalism like logic.

How do we fare here as concerns consciousness? Its reality is one of the matters in question. The independent reality of consciousness is controversial. We cannot demonstrate, physically, that it is real. On the other hand, as all evidence of any kind emerges through experience it seems strange to insist that our experience is nothing but illusion. What happens to the evidential status of physics itself if the consciousness that interprets physical evidence as such is only an illusion? Can evidence be real if the status of the “evidence interpreter” is not? What happens to the truth status of the proposition “physics is causally closed” if the subjective arena asserting that proposition is an illusion?

This threat to the veracity of physics is a real problem for physicalists who insist that consciousness cannot be real. It at least suggests that it might be real, that its reality cannot be ruled out by fiat and might have to be accepted for the sake of our seeming capacity to comprehend the world.

The evidence for the non-material character of consciousness also emerges in consciousness! An idea cannot be weighed but it nevertheless appears that ideas are instrumental in the process of moving our bodies and thus our capacity to control aspects of the world confirming the correspondence between experience and physics. All of human society, our technological infrastructure, political institutions, and history are a function of this relation between quintessentially non-material ideas and the physical world. Somewhere in the distant past lies an ancestor, a hunter-gatherer who carried a club and a piece of chipped flint. Having both of these objects and a knowledge of making rope or twine from plant stems, this ancestor thought to attempt tying the flint and the club together producing something novel and more utilitarian than either the flint or club alone. An idea became a physical thing, an ax, through the controlled (purposeful) movement of a body that tied the flint and club together.

Many of the actions we take appear, to experience, related to the ideas we have. Using our bodies, we can pattern the physical by mapping ideas onto it. This is what I spoke of above as a “connecting up”. That I use an idea, a mental picture perhaps of some intended physical end-product, along with appropriate motions of my body, to produce that end product. The connection between the idea and the end product is obvious and immediate to us. It is not a connection between the physical and something non-physical outside of ourselves (magic unicorns perhaps), but between ourselves (subjective experience), our bodies, and the final physical output. We understand that our physical hands fashioned the physical end-product and that our hands moved in response to physical nerve impulses. The connection backs up to what it was that set those nerve impulses in action; a non-physical idea coupled with a non-physical intent to attempt its implementation (a mapping) in the physical.

We take this relation so “for granted” that mostly we do not even notice it. The productive conjunction between ideas and objects, mediated by bodies, means that ideas are real. Through the mediating influence of the controlled body ideas are causally efficacious. This could not be so if ideas were nothing more than illusions. True ideas have correlative brain states that are physical, but we do not subjectively manipulate brain states. We juggle ideational contents of subjective consciousness directly and these have a quintessentially non-material character.

The non-material quality of ideas is not of course proven by their association with physical actions whose consequences are also manifest in consciousness. Deterministic brain states not manipulated in consciousness might result in both ideas (and all of consciousness) and movement thus explaining their apparent connection. If this were true however it would have to be true about every product of humanity from the first struck flint to the space station and for that matter all the institutions and historical contingencies resulting in the present state-of-the-world. A staggering set of deterministic coincidences for which we, that is subjective experience, can take no credit whatsoever.

One cannot have this both ways. Either the subjective arena has no causal efficacy whatsoever or there is here a genuine connection between non-material cause and physical effect. If we wish to suspend judgement on this dilemma we yet must acknowledge that subjective experience does at least rule out physicalist declarations of its impossibility. Our experience counts as enough evidence for the reality of the non-material to question the physicalist assertion that there cannot possibly be anything other than the physical in the universe. Subjective experience seems to be telling us that the non-material is real and the entire history of human civilization at least warrants our concession to the possibility.

The evidence suggests, if it does not formally demonstrate, that something real and non-material is possible and obtains inside the otherwise physical universe. Consciousness (broadly speaking) is that reality. All of the philosophers cited above are materialists but not physicalists. They share with the physicalists a conviction that everything inside the material universe, including consciousness, takes origin in nothing more than the physical. They break with the physicalists in asserting the non-physical can, in fact, emerge from the purely physical and that in this universe, consciousness is that non-physical emergent entity.

Once emerged, they assert, the non-material cannot be fully traced-back to the physical. Subjective experience is not merely another viewpoint, another way of “looking at” something physical, but a novel thing in itself. Once it comes to be, from out of the physical, it can no longer be fully reduced to the physical. This view is called “property dualism”. Two phenomenon, mind and physics, but ultimately a single source, physics. But this view has its own problem with the contents and qualities of experience. Even if the non-material cannot be reduced in any logical way to the physical (more or less the position of all the philosophers cited above) it must, nevertheless originate from nothing more than the physical and this means that some evidence of the transformation from physical to non-physical should lie in the physical past, in the history of the universe. That no such evidence has ever been observed is not proof that non-material origins are not purely physical.

To date no mechanism has been discovered in physics that would plausibly result in such a transformation. If it is true that no such mechanism exists, physics is really causally closed, then the emergence of the non-physical from the physical alone is not possible and no historical marks are there to be found!

Every one of these property dualist theories of the non-material amounts to presupposing either an opening in causal closure or an invisible (to physics) set of causal laws or properties in the physical that add the qualities (to physics) required to produce the non-material. The first approach implies some evidence of itself within physics as noted in the previous paragraph. None has been found, and none of our present theories of the world require any provision for it.

Metaphysically speaking, the second approach is no less supernatural than the hypothesis of a divine being. It may lack the being’s anthropomorphic qualities but its presence and interaction with the physical are no less inexplicable. The “coming to be” of these psycho-physical laws (Chalmers’ term) wants explaining, and their interaction with the physical is no less a mystery than the interaction problem posed by a substance-dualism of mind or for that matter God. For a more detailed treatment of this issue specifically see my “Fantasy Physics and the Genesis of Mind”

To wrap up I summarize what I hope I have accomplished.

1. Physics can measure only the physical.

2. Physics leaves in abeyance the question of some non-material reality inside the physical universe. It remains logically possible. Physics has no evidence for it, but all physics can assert with authority is that explanations of indisputably physical phenomena require no reference to it.

3. There are subjective observers inside the physical universe. These observers all have bodies made of matter and subject to measurement by physics. But they also have “subjective experience” whose qualities are not subject to physical measurement.

4. Either the qualities of subjective experience are not real or they are real and can make some contribution to physical cause; they can configure physical cause (movement of a body) to produce physical effects patterned by a non-material idea. The non-material idea can be mapped to physical reality or put conversely physical reality can be patterned, configured, by non-material ideas.

5. Either the whole of human history and achievement is a blind accident or non-material ideas are causally efficacious and therefore must be real.

In “An Epistemological Argument for Free Will” I argue that free will is real and our experience warrants that belief. None of what is discussed above impinges directly on free will. Our ideas might be both real and non-material without our having free will. The connection between ideas and the physical might, after all, be fully determined even if ideas are in fact the initial patterns of the physical result. But the subsequent free will argument does rest, metaphysically, on the reality and non-materiality of consciousness.