The first purpose of this article is to explain the nature of the connection between mind and matter and how orthodox quantum mechanics is both dualistic and nondualistic: it is dualistic on a pragmatic, operational level, but is nondualistic on a deeper ontological level.

The second purpose is to reconcile a meaningful concept of human freedom with the principle of sufficient reason; with the principle that nothing happens without a sufficient reason.

To lay a framework for discussing these two issues I shall begin by describing some contrasting ideas about the nature of reality advanced by three towering intellectual figures, Rene Descartes (1596-1650), Isaac Newton (1642-1727), and William James (1842-1910).

René Descartes conceived nature to be divided into two parts: a mental part and a physical part. The mental part, which he called "res cogitans", contains our thoughts, ideas, and feeling, whereas the physical part, called "res extensa", is defined here to be those aspects of nature that we can describe by assigning mathematical properties to space-time points. Examples of physical aspects of our understanding of nature are trajectories of physical particles, the electric field E(x,t), and the quantum mechanical field (operator) A(x,t). Descartes allowed the mental and physical aspects to interact with each other, but only for those physical parts that are located inside human brains. This is the classic Cartesian notion of duality.

Isaac Newton built the foundations of "modern physics" upon the ideas of Descartes, Galileo, and Kepler. The astronomical observations of Tycho Brahe led to Kepler’s three laws of planetary motion. These laws, coupled to Galileo’s association of gravity with acceleration, led directly to Newton’s inverse square law of gravitational attraction, and his general laws of motion. Newton extended these dynamical ideas, with tremendous success, down to the scale of terrestrial motions, to the tides and falling apples etc.. He also conjectured an extension down to the level of the atoms. According to that hypothesis, the entire physically described universe, from the largest objects to the smallest ones, would be bound by the precept of physical determinism, which is the notion that a complete description of the values of all physically described variables at any one time determines with certainty the values of all physically described variables at any later time. This idea of universal physical determinism is a basic precept of the development of Newtonian dynamics into what is called "classical physics".

1a. The Omission of the Phenomenal Aspects of Nature

The dynamical laws of classical physics are formulated wholly in terms of physically described variables: in terms of the quantities that Descartes identified as elements of "res extensa". Descartes’ complementary psychologically described things, the elements of his "res cogitans", were left completely out: there is, in the causal dynamics of classical physics, no hint of their existence. Thus there is not now, nor can there ever be, any rational way to explain, strictly on the basis of the dynamical precepts of classical physics, either the existence of, or any causal consequence of, the experientially described aspects of nature. Yet these experiential aspects of nature are all that we actually know.

This troublesome point was abundantly clear already at the outset:

Newton: "…to determine by what modes or actions light produceth in our minds the phantasm of colour is not so easie."

Leibniz: "Moreover, it must be confessed that perception and that which depends upon it are inexplicable on mechanical grounds, that is to say, by means of figures and motions."

Classical physics, by omitting all reference to the mental realities, produces a logical disconnect between the physically described properties represented in that theory and the mental realities by which we come to know them. The theory allows the mental realities to know about the physical aspects of nature, yet be unable to affect them in any way. Our mental aspects are thereby reduced to "Detached Observers", and Descartes’ duality collapses, insofar as the causally closed physical universe is concerned, to a physics-based nonduality; to a physical monism, or physicalism. Each of us rejects in actual practice the classical-physics claim that our conscious thoughts and efforts can have no affects on our physical actions. We build our lives, and our political, judicial, economic, social, and religious institutions, upon the apparently incessantly reconfirmed belief that, under normal wakeful conditions, a person’s intentional mental effort can influence his physical actions.

William James, writing in 1892, challenged, on rational grounds, this classical-physics-based claim of the impotence of our minds. At the end of his book Psychology: The Briefer Course he reminded his readers that "the natural science assumptions with which we started are provisional and revisable things". That was a prescient observation! Eight years later Max Planck discovered a new constant of nature that signaled a failure of the precepts of classical physics, and by 1926 the precepts of its successor, quantum mechanics, were firmly in place.

The most radical shift wrought by quantum mechanics was the explicit introduction of mind into the basic conceptual structure. Human experience was elevated from the role of ‘a detached observer’ to that of ‘the fundamental element of interest’:

Bohr: "In our description of nature the purpose is not to disclose the real essence of phenomena but only to track down as far as possible relations between the multifold aspects of our experience." (Bohr, 1934, p.18).

Bohr: "The sole aim [of quantum mechanics] is the comprehension of observations…(Bohr, 1958, p.90).

Bohr: The task of science is both to extend the range of our experience and reduce it to order (Bohr, 1934, p.1)

Heisenberg: "The conception of the objective reality of the elementary particles has evaporated not into the cloud of some new reality concept, but into the transparent clarity of a mathematics that represents no longer the behaviour of the particles but our knowledge of this behavior" (Heisenberg, 1958a, p. 95).

This general shift in perspective was associated with a recasting of physics from a set of mathematical connections between physically described aspects of nature, into set of practical rules that, eschewing ontological commitments, predicted correlations between various experiential realities on the basis of their postulated dynamical links to certain physically describable aspects of our theoretical understanding of nature.

In view of this fundamental re-entry of mind into basic physics, it is nigh on incomprehensible that so few philosophers and non-physicist scientists entertain today, more than eight decades after the downfall of classical physics, the idea that the physicalist conception of nature, based on the invalidated classical physical theory, might be profoundly wrong in ways highly relevant to the mind-matter problem.

Philosophers are often called upon to defend highly counter-intuitive and apparently absurd positions. But to brand as an illusion, and accordingly discount, the supremely successful conceptual foundation of our lives---the idea that our conscious efforts can influence our physical actions---on the basis of its conflict with a known-to-be-false theory of nature that leaves out all that we really know, is a travesty against reason, particularly in view of the fact that the empirically valid replacement of that empirically invalid classical theory is specifically about the details of the connection between our consciously chosen intentional actions and the experiential feedbacks that such actions engender.

1b. Von Neumann’s Dualistic Quantum Mechanics.

The logician and mathematician John von Neumann (1955/1932) formalized quantum mechanics in a way that allowed it to be interpreted as a dualistic theory of reality in which mental realities interact in specified causal ways with physically described human brains. This orthodox quantum ontology is in essential accord with the dualistic ideas of Descartes.

An objection often raised against Cartesian dualism is couched as the query: How can ontologically distinct aspects of nature ever interact? Must not nature consist ultimately of one fundamental kind of stuff in order for its varied components to be able to cohere.

This objection leads to a key question: What is the ontological character of the physical aspect of quantum mechanics?

2. The Ontological Character of the Physical Aspect of the Orthodox (von Neumann-Heisenberg) Quantum Mechanics.

The physical aspect of the quantum mechanical conception of nature is represented by the quantum state. This state is physical, in the defined sense that we can describe it by assigning mathematical properties to space-time points. But this physical aspect is does not have the ontological character of a material substance, in the sense in which the physical world of Newtonian (or classical) physics is made of material substance: it does not always evolve in a continuous manner, but is subject to abrupt "quantum jumps", sometimes called "collapses of the wave function".

Heisenberg (1958b) couched his understanding of the ontological character of the reality lying behind the successful quantum rules in terms of the Aristotelian concepts of "potentia" and "actual" . The quantum state does not have the ontological character of an "actual" thing. It has, rather, the ontological character of "potentia": of a set of "objective tendencies for actual events to happen". An actual event, in the von Neumann-Heisenberg orthodox ontology, is "The discontinuous change in the probability function [that] takes place with the act of registration…in the mind of the observer". (Heisenberg, 1958b, p. 55)

The point here is that in orthodox (von Neumann-Heisenberg) quantum mechanics the physical aspect is represented by the quantum state, and this state has the ontological character of potentia---of objective tendencies for actual events to happen. As such, it is more mind-like than matter-like in character. It involves not only stored information about the past, but also objective tendencies pertaining to events that have not yet happened. It involves projections into the future, elements akin to imagined ideas of what might come to pass. The physical aspects of quantum mechanics are, in these ways, more like mental things than like material things.

Furthermore, a quantum state represents probabilities. Probabilities are not matter-like. They are mathematical connections that exist outside the actual realities to which they pertain. They involve mind-like computations and evaluations: weights assigned by a mental or mind-like process.

Quantum mechanics is therefore dualistic in one sense, namely the pragmatic sense. It involves, operationally, on the one hand, aspects of nature that are described in physical terms, and, on the other hand, also aspects of nature that are described in psychological terms. And these two parts interact in human brains in accordance with laws specified by the theory. In these ways orthodox quantum mechanics is completely concordant with the defining characteristics of Cartesian dualism.

Yet, in stark contrast to classical mechanics, in which the physically described aspect is matter-like, the physically described aspect of quantum mechanics is mind-like! Thus both parts of the quantum Cartesian duality are ontologically mind-like.

In short, orthodox quantum mechanics is Cartesian dualistic at the pragmatic/operational level, but mentalistic on the ontological level.

This conclusion that nature is fundamentally mind-like is hardly new. But it arises here not from some deep philosophical analysis, or religious insight, but directly from an examination of the causal structure of our basic scientific theory.

3. Natural Process, Sufficient Reason, and Human Freedom.

There are two fundamentally different ways to cope with the demands of the theory of relativity.

The first is the classical-physics-based Einsteinian idea of a Block Universe: a universe in which the entire future is laid out beforehand, with our experiences being mere perspectives on this preordained reality, viewed from particular vantage points in spacetime.

A second way to accommodate, rationally, the demands of special relativity is the quantum-physics-based Unfolding Universe, in which facts and truths become fixed and definite in the orderly way allowed by relativistic quantum field theory (Tomonaga, 1946; Schwinger 1951; Stapp, 2007, p. 92) with our experiences occurring in step with the coming into being of definite facts and truths.

I subscribe to the latter idea: to the idea of an unfolding reality in which each experienced increment of knowledge is associated with an actual event in which certain facts or truths become fixed and definite.

I also subscribe to the idea that this unfolding conforms to the principle of sufficient reason, which asserts that no fact or truth can simply "pop out of the blue", with no sufficient reason to be what it turns out to be.

An important question, then, is whether such a concordance with the principle of sufficient reason precludes the possibility of meaningful human freedom. Is human freedom an illusion, in the sense that every action that a person makes was fixed with certainty already at the birth of the universe?

Laplace’s classical argument for the "certainty of the future" states (in condensed form):

"For a sufficiently powerful computing intellect that at a certain moment knew all the laws and all the positions, nothing would be uncertain, and the future, just like the past, would be present before its eyes."

This view argues for "certainty about the future"; for a certainty existing at an earlier moment on the basis of information existing at that earlier moment. It contemplates:

1. A computing intellect existing outside or beyond nature itself, able to "go" in thought where the actual evolving universe has not yet gone.

2. Invariant causal laws.

But nothing really exists outside the whole of nature itself! Thus nature itself must make its own laws/habits. And these habits could themselves evolve. Even if there is a sufficient reason, within the evolving reality, for every change in the laws, and every generation of a fact, it is not evident that any intellect standing outside the evolving reality itself could compute, on the basis of what exists at a certain moment, all that is yet to come. For the evolution of reason-based reasons may be intrinsically less computable than the evolution of the mathematically formulated physically described properties of the classical-physics approximation to the actual laws of nature. Reason encompasses computable mathematics, but computable mathematics may not encompass reason. Reason is a category of explanation more encompassing than mathematical computation.

The laws of classical mechanics are cast in a particular kind of mathematical form that allows, in principle, a "mathematical computation" performed at an early time to predict with certainty the state of the universe at any later time. But this is very special feature of classical mechanics. It is far from obvious that the---definitely nonclassical---real world must exhibit this peculiar ‘computability" feature.

The notion that a reason-based unfolding of the actual world is computable is an extrapolation from the classical-physics approximation that is far too dubious to provide the basis of a compelling argument that, in a mind-based quantum universe evolving in accordance with the principles of both quantum mechanics and sufficient reason, the outcomes of human choices are certain prior to their actual occurrence. It is far from being proved that, in a universe of that kind, the exact movement of the computer key that I am now pressing was certain already at the birth of the universe. "Reasons" could lack the fantastic computability properties that the physically described features of classical physics enjoy. But in that case our present reason-based human choices need not have been fixed with certainty at the birth of the universe. Within orthodox quantum mechanics meaningful human freedom need not be an illusion.

4. Reason-Based Dynamics Versus Physical-Description-Based Dynamics.

The arguments given above rest heavily upon the contrast between the reason-based dynamics of the unfolding universe described by quantum mechanics and the physical-description-based dynamics of the block universe described by classical mechanics. In this final section I shall pinpoint the technical features of orthodox quantum mechanics that underlie this fundamental difference between these two theories.

Von Neumann created a formulation of quantum mechanics in which all the physical aspects of nature are represented by the evolving quantum mechanical state (density matrix) of the universe. Each subsystem of this physically described universe is represented by a quantum state obtained by performing a certain averaging procedure on the state of the whole universe. Each experience of a person is associated with an "actual event". This event reduces, in a mathematically specified way, the prior quantum state of this person’s brain---and consequently the quantum state of the entire universe---to a new "reduced" state. The reduction is achieved by the removal of all components of the state of this person’s brain that are incompatible with the increment of knowledge associated with the experience. The needed mapping between "experiential increments in a person’s knowledge" and "reductions of the quantum mechanical state of that person’s brain" can be understood as being naturally created by trial and error learning of the experienced correlations between intentional efforts and the experiential feedbacks that these efforts tend to produce.

A key feature of von Neumann’s dynamics is that it has two distinct kinds of mind-brain interaction. Von Neumann calls the first of these two processes "process 1". It corresponds to a choice of a probing action by the person, regarded as an agent or experimenter. The second kind of mind-brain interaction was called by Dirac "a choice on the part of nature". It specifies nature’s response to the probing action selected by a logically preceding process 1 action. Von Neumann uses the name "process 2" to denote the physical evolution that occurs between the mind-brain (collapse) interactions. I therefore use the name "process 3" to denote the reduction/collapse process associated with nature’s response to the process 1 probing action.

The mathematical form of process 1 differs from that of process 3. This mathematical difference causes these two processes to have different properties. In particular, process-1 actions have only local effects, in the sense that the dependence of the predictions of quantum mechanics upon a process-1 action itself, without a specification of the response, is confined (in the relativistic version) to the forward light-cone of the region in which the process-1 physical action occurs: the empirically observable effects of a process-1 action never propagate faster than the speed of light. On the other hand, nature’s response (process 3) to a localized process-1 action can have observable statistical effects in a faraway contemporaneous region. The no-faster-than-light property of the empirically observable effects of any process-1 action is what justifies the word "relativistic" in relativistic quantum theory, even though the underlying mathematical description involves abrupt process-1-dependent faster-than-light transfers of information in connection with nature’s response to the process-1 action.

Process 2 is a generalization of the causal process in classical mechanics, and, like it, is deterministic: the state of the universe at any earlier time completely determines what it will evolve into at any later time, insofar as no process 1 or process 3 event intervenes. But if no process 1 or process 3 event intervenes then the process 2 evolution would take the initial "big bang" state of the universe into a gigantic smear in which, for example, the moon would be smeared out over the night sky, and the mountains, and the cities, and we ourselves, would all be continuously spread out in space.

It is the process 1 and process 3 actions that, in the orthodox ontology, keep the universe in line with human experiences. On the other hand, the von Neumann ontology certainly does not exclude the possibility that non-human-based analogs of the human-based process 1 and follow-up process 3 actions also exist. Rather, it explains why the existence of reduction processes associated with other macroscopic agents would be almost impossible to detect empirically. These features of the von Neumann ontology justify focusing our attention here on the human involvement with nature.

Process 1, unlike process 2, is not constrained by any known law. In actual practice our choices of our probing actions appear to us to be based on reasons. We open the drawer in order to find the knife, in order to cut the steak, in order to eat the steak, in order to satisfy our hunger. Whilst all of this chain of reasons would, within the deterministic framework of classical physics, need to be, in principle, explainable in mathematical ways based upon the physical description of the universe, there is no such requirement in orthodox quantum mechanics: the sufficient reasons could be "reasons"; reasons involving the experiential dimension of reality, rather than being fully determined within the physical dimension. And these reasons could be, at each individual moment of experience, sufficient to determine the associated process 1 choice, without those choices having been mathematically computable from the state of the universe at earlier times.

The process 3 selection on the part of nature, unlike the process 1 choice, is not completely unconstrained: it is constrained by a statistical condition. According to the principle of sufficient reason, the process 3 choice must also be, in principle, determined by a sufficient reason. But, as emphasized above, nature’s choice is nonlocal in character. Thus the reason for a process 3 choice need not be located at or near the place where the associated process 1 action occurs. Yet, as was clear already in classical statistical mechanics, there is an á priori statistical rule: equal volumes of phase space are equally likely. The (trace-based) statistical rule of quantum mechanics is essentially the quantum mechanical analog of this á priori statistical rule. The quantum statistical rule is therefore the natural statistical representation of the effect of a reason-based choice that is physically far removed from its empirical process 3 manifestation.

In closing, it is worth considering the argument of some physicalist philosophers that the replacement of classical mechanics---upon which physicalism is based---by quantum mechanics is not relevant to the resolution of the mind-matter problem for the following reason: that replacement has no bearing on the underlying problem of human freedom. The argument is that the essential difference between the two theories is (merely) that the determinism of classical mechanics is disrupted by the randomness of quantum mechanics, but that an introduction of randomness into the dynamics in no way rescues the notion of meaningful human freedom: a random choice is no better than a deterministic choice as an expression of meaningful human freedom.

This physicalist argument flounders on the fact that the element of quantum randomness enters quantum mechanics only via process 3, which delivers nature’s choice. Man’s choice enters via process 1, which is the logical predecessor to nature’s process 3 "random" choice. In orthodox quantum mechanics, no elements of quantum randomness enter into man’s choice. Nor is man’s choice fixed by the deterministic aspect of quantum mechanics: that aspect enters only via process 2. Von Neumann’s process 1 human choice is, in this very specific sense, "free": it is von Neumann’s representation of Bohr’s "free choice of experimental arrangement for which the quantum mechanical formalism offers the appropriate latitude" (Bohr 1958. p.51). Human choices enter orthodox quantum mechanics in a way not determined by a combination of the deterministic and random elements represented in the theory.

Bohr, N. (1934). Atomic Physics and the Description of Nature. Cambridge University Press, Cambridge, UK.

Bohr, N. (1958). Atomic Physics and Human Knowledge. Wiley, New York, US.

Heisenberg, W. (1958a). The representation of ature in contemporary physics. Daedalus, 87 (summer), 95-108.

Heisenberg, W. (1958b). Physics and Philosophy. Harper, New York, US.

James. W. (1892). Psychology: The Briefer Course. In: William James: Writings 1879-1899. Library of America (1992), New York, US.

Schwinger, J. (1951). Theory of Quantized Fields 1. Physical Review, 82, 914-927.

Stapp, H.P. (2007). Mindful Universe: Quantum Mechanics and the Participating Observer. Springer, Berlin.

Tomonaga, S. (1946). On a relativistically invariant formulation of the quantum theory of wave fields. Progress of Theoretical Physics, 1, 27-42.

Von Neumann, J. (1955/1932). Mathematical Foundations of Quantum Mechanics. Princeton University Press, Princeton New Jersey, US. (Translation of the German original: Mathematische Grundlagen der Quantenmechanik, Springer, Berlin, 1932.)