Two-stage model of free will

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A two-stage model of free will separates the free stage from the will stage.

In the first stage, alternative possibilities for thought and action are generated, in part indeterministically.
In the second stage, an adequately determined will evaluates the options that have been developed.

If, on deliberation, one option for action seems best, it is selected and chosen. If no option seems good enough, and time permitting, the process can return to the further generation of alternative possibilities ("second thoughts") before a final decision.

A two-stage model can explain how an agent could choose to do otherwise in exactly the same circumstances that preceded the first stage of the overall free will process.

The standard argument against free will[edit]

The two-stage argument is designed to defeat the standard argument against free will. In that very simple and logical argument:

  • P1. Either determinism or indeterminism is true
    (The philosopher J. J. C. Smart points out that these exhaust the logical possibilities.)
  • P2. If determinism is true, we are not free.
  • P3. If indeterminism is true, our decisions are random and we lack responsibility (or, anyway, control is lacking).

In the first "free" stage of the two-stage model, the indeterminism is limited to the generation of alternative possibilities, it does not directly cause the willed decision, thus negating P2.

In the second "will" stage, the decision is not predetermined by events in the distant past, before the agent was born, indeed possibly back to the origin of the universe in the extreme determinism view.

Identifying the source of indeterminism in the free stage, and locating it in the brain, has proved to be a challenge for philosophers and scientists. A random quantum mechanical event in the brain amplified to the macroscopic level might only do harm if it was involved directly in the decision.

Comparison to biological evolution[edit]

Ernst Mayr called biological evolution a "two-step process", in which random variations in the gene pool are followed by law-like natural selection.[1]

Free will is also a two-stage creative process – first random and "free", then a lawful "will". First chance, then choice.

The mind's "two-stage" ability to be creative and free is likely evolved indirectly from Mayr's "two-step" process and then directly from the combination of random and lawlike behavior in the lower animals pointed out by Martin Heisenberg.[2] Free will is therefore not an ad hoc development in humans, as many philosophers (especially theologians) have thought.

Getting from behavioral freedom in the lower animals to free will in humans has primarily involved significant changes in the complexity of the second stage – the selection process.

Although randomness may at all levels have the same source in chaotic thermal and quantal noise, we can note that the selection process itself has significantly evolved. So we can suggest different levels of selection (but note that each level organisms all using the earlier levels).

  • Natural selection – for biological evolution, selection is reproductive success for a population.
  • Instinctive selection – by animals with little or no learning capability. Selection criteria are transmitted genetically.
  • Learned selection – for animals whose past experiences guide current choices. Selection criteria are acquired environmentally, including instruction by parents and peers.
  • Predictive selection – using imagination and foresight to evaluate the future consequences of choices.
  • Reflective and normative selection – in which conscious deliberation about cultural values influences the choice of behaviors.

Evolution has added more and more features over time that eventually become the many factors at work in the fully conscious human will.

Two-stage models[edit]

William James, Henri Poincaré, Arthur Holly Compton, Karl Popper, Daniel Dennett, Henry Margenau, Robert Kane, David Sedley and Anthony Long, Alfred Mele and Martin Heisenberg have all proposed two-stage models.

William James[edit]

In 1884, William James was the first thinker to propose a two-stage model.

In his picture of free will, indeterminism is the source for what James called "alternative possibilities" and "ambiguous futures." The chance generation of such alternative possibilities for action does not in any way limit his choice to one of them. Notice that for James chance is not the direct cause of actions. James makes it clear that it is his choice that "grants consent" to one of them.

In 1884 James asked some Harvard Divinity School students to consider his choice for walking home after his talk.

What is meant by saying that my choice of which way to walk home after the lecture is ambiguous and matter of chance?...It means that both Divinity Avenue and Oxford Street are called but only one, and that one either one, shall be chosen.[3]

With this simple example, James was the first thinker to enunciate clearly a two-stage decision process, with chance in a present time of random alternatives, leading to a choice which grants consent to one possibility and transforms an equivocal ambiguous future into an unalterable and simple past. There is a temporal sequence of undetermined alternative possibilities followed by an adequately determined choice where chance is no longer a factor.

James also gave full credit to Charles Darwin for the core idea behind his own "mental evolution", explicitly connecting spontaneous variations in the Darwinian gene pool with random images and thoughts in the human brain.

[In mental evolution], if anywhere, it would seem at first sight as if that school must be right which makes the mind passively plastic, and the environment actively productive of the form and order of its conceptions; which, in a word, thinks that all mental progress must result from a series of adaptive changes, in the sense already defined of that word...It might, accordingly, seem as if there were no room for any agency other than this; as if the distinction we have found so useful between "spontaneous variation", as the producer of changed forms, and the environment, as their preserver and destroyer, did not hold in the case of mental progress; as if, in a word, the parallel with Darwinism might no longer obtain… And I can easily show...that as a matter of fact the new conceptions, emotions, and active tendencies which evolve are originally produced in the shape of random images, fancies, accidental out-births of spontaneous variation in the functional activity of the excessively instable human brain. [4]

Henri Poincaré[edit]

Henri Poincaré was called the "last universalist" because he was a great contributor to so many fields in mathematics, but his work was also broad in physics, philosophy, and psychology. William James read Poincaré and the great thinker knew James work, but there is no sign of any direct influence.

Around 1906 Poincaré speculated on how his mind works when he is solving mathematical problems. He had the critical insight that random combinations and possibilities are generated, some in an unconscious way with chance involved, then they are selected among, perhaps initially also by an unconscious process, but then by a definite conscious process of validation.

It is certain that the combinations which present themselves to the mind in a kind of sudden illumination after a somewhat prolonged period of unconscious work are generally useful and fruitful combinations… all the combinations are formed as a result of the automatic action of the subliminal ego, but those only which are interesting find their way into the field of consciousness… A few only are harmonious, and consequently at once useful and beautiful, and they will be capable of affecting the geometrician's special sensibility I have been speaking of; which, once aroused, will direct our attention upon them, and will thus give them the opportunity of becoming conscious… In the subliminal ego, on the contrary, there reigns what I would call liberty, if one could give this name to the mere absence of discipline and to disorder born of chance. [5]

Arthur Holly Compton[edit]

In 1931, Nobel prize-winning physicist Arthur Holly Compton championed the idea of human freedom based on quantum uncertainty and invented the notion of amplification of microscopic quantum events to bring chance into the macroscopic world. In his somewhat bizarre mechanism, he imagined sticks of dynamite attached to his amplifier, anticipating the Schrödinger's cat paradox.[6]

Years later, Compton clarified the two-stage nature of his idea in an Atlantic Monthly article in 1955.

A set of known physical conditions is not adequate to specify precisely what a forthcoming event will be. These conditions, insofar as they can be known, define instead a range of possible events from among which some particular event will occur. When one exercises freedom, by his act of choice he is himself adding a factor not supplied by the physical conditions and is thus himself determining what will occur. That he does so is known only to the person himself. From the outside one can see in his act only the working of physical law. It is the inner knowledge that he is in fact doing what he intends to do that tells the actor himself that he is free. [7]

Karl Popper[edit]

Compton's work was no doubt closely read by philosopher Karl Popper, especially when Popper was selected to give the first Arthur Holly Compton Memorial Lecture in 1965. At first Popper dismissed quantum mechanics as being no help with free will, but later he describes a two-stage model that parallels Darwinian evolution, with genetic mutations being probabilistic and involving quantum uncertainty.

In 1965 Popper called for a combination of randomness and control to explain freedom, though not yet explicitly in two stages with random chance before the controlled decision.

[F]reedom is not just chance but, rather, the result of a subtle interplay between something almost random or haphazard, and something like a restrictive or selective control. [8]

In his 1977 book with John Eccles, The Self and its Brain, Popper finally formulates the two-stage model in a temporal sequence, and makes the comparison with evolution and natural selection,

New ideas have a striking similarity to genetic mutations. Now, let us look for a moment at genetic mutations. Mutations are, it seems, brought about by quantum theoretical indeterminacy (including radiation effects). Accordingly, they are also probabilistic and not in themselves originally selected or adequate, but on them there subsequently operates natural selection which eliminates inappropriate mutations. Now we could conceive of a similar process with respect to new ideas and to free-will decisions, and similar things.

That is to say, a range of possibilities is brought about by a probabilistic and quantum mechanically characterized set of proposals, as it were - of possibilities brought forward by the brain. On these there then operates a kind of selective procedure which eliminates those proposals and those possibilities which are not acceptable to the mind. [9]

In 1977 Popper gave the first Darwin Lecture, at Darwin College, Cambridge. He called it Natural Selection and the Emergence of Mind. In it he said he had changed his mind (a rare admission by a philosopher) about two things. First he now thought that natural selection was not a "tautology" that made it an unfalsifiable theory. Second, he had come to accept the random variation and selection of ideas as a model of free will.

The selection of a kind of behavior out of a randomly offered repertoire may be an act of free will. I am an indeterminist; and in discussing indeterminism I have often regretfully pointed out that quantum indeterminacy does not seem to help us;[10] for the amplification of something like, say, radioactive disintegration processes would not lead to human action or even animal action, but only to random movements.

I have changed my mind on this issue.[11] A choice process may be a selection process, and the selection may be from some repertoire of random events, without being random in its turn. This seems to me to offer a promising solution to one of our most vexing problems, and one by downward causation.[12]

Henry Margenau[edit]

In 1968, physicist Margenau was invited to give the Wimmer Lecture at St. Vincent College in Pennsylvania. His topic was Scientific Indeterminism and Human Freedom. Margenau embraced indeterminism as the first step toward a solution of the problem of human freedom.

Then in 1982, with co-author Lawrence LeShan, Margenau called his model of free will a "solution" to what had heretofore had been seen as mere "paradox and illusion." He very neatly separates "free" and "will" in a temporal sequence, as William James had done, naming them simply "chance" followed by "choice".

Our thesis is that quantum mechanics leaves our body, our brain, at any moment in a state with numerous (because of its complexity we might say innumerable) possible futures, each with a predetermined probability. Freedom involves two components: chance (existence of a genuine set of alternatives) and choice. Quantum mechanics provides the chance, and we shall argue that only the mind can make the choice by selecting (not energetically enforcing) among the possible future courses.[13]

Daniel Dennett[edit]

While he is a confirmed compatibilist, in "On Giving Libertarians What They Say They Want"—Chapter 15 of his 1978 book Brainstorms—Tufts philosopher Daniel Dennett articulated the case for a two-stage model of free will.

Dennett named his model of decision-making "Valerian" after the poet Paul Valéry, who took part in a 1936 conference in Paris with Jacques Hadamard. The conference focused on Henri Poincaré's two-stage approach to problem solving, in which the unconscious generates random combinations. In his book The Psychology of Invention in the Mathematical Mind, Hadamard quoted Valéry (as did Dennett later), summarizing the conference opinion,

It takes two to invent anything. The one makes up combinations; the other one chooses, recognizes what is important to him in the mass of things which the former has imparted to him.

Although Valery describes two persons, this is clearly William James's temporal sequence of random chance ("free") followed by a determining choice ("will"). For James, chance and choice are part of a single mind. This two-stage mind model is better named "Jamesian" free will.

Dennett makes his version of a two-stage model very clear, defending it with six reasons. However, Dennett remains a compatibilist.

The model of decision making I am proposing has the following feature: when we are faced with an important decision, a consideration-generator whose output is to some degree undetermined produces a series of considerations, some of which may of course be immediately rejected as irrelevant by the agent (consciously or unconsciously). Those considerations that are selected by the agent as having a more than negligible bearing on the decision then figure in a reasoning process, and if the agent is in the main reasonable, those considerations ultimately serve as predictors and explicators of the agent's final decision.

Dennett gives his reasons why this is the kind of free will that libertarians say they want.

1. "First...The intelligent selection, rejection, and weighing of the considerations that do occur to the subject is a matter of intelligence making the difference."

2. "Second, I think it installs indeterminism in the right place for the libertarian, if there is a right place at all."

3. "Third...from the point of view of biological engineering, it is just more efficient and in the end more rational that decision making should occur in this way."

4. "A fourth observation in favor of the model is that it permits moral education to make a difference, without making all of the difference."

5. "Fifth - and I think this is perhaps the most important thing to be said in favor of this model - it provides some account of our important intuition that we are the authors of our moral decisions."

6. "Finally, the model I propose points to the multiplicity of decisions that encircle our moral decisions and suggests that in many cases our ultimate decision as to which way to act is less important phenomenologically as a contributor to our sense of free will than the prior decisions affecting our deliberation process itself: the decision, for instance, not to consider any further, to terminate deliberation; or the decision to ignore certain lines of inquiry.

"These prior and subsidiary decisions contribute, I think, to our sense of ourselves as responsible free agents, roughly in the following way: I am faced with an important decision to make, and after a certain amount of deliberation, I say to myself: "That's enough. I've considered this matter enough and now I'm going to act", in the full knowledge that I could have considered further, in the full knowledge that the eventualities may prove that I decided in error, but with the acceptance of responsibility in any case." [14]

Robert Kane[edit]

In his 1985 book Free Will and Values. Kane carefully considered the work of Compton, Popper and Eccles, and Dennett. He developed his own two-stage model in the book but in the end he did not endorse it because it "did not go far enough."

Kane was actually quite bleak about the possibilities for a satisfactory libertarian model. He felt

that any construction which escaped confusion and emptiness was likely to fall short of some libertarian aspirations - aspirations that I believe cannot ultimately be fulfilled.[15]

His model was a choice between "relativistic alternatives." The choice was in part rational and in part random. It could be explained by the agent giving his reasons. Even if the choice is by chance,

the agent has agreed beforehand to accept the chance selected outcome and to endorse reasons for it in a special way. That is, the selection is going to be 'willed to be so' on a provisional basis by the agent, whichever way it goes. [16]

Kane hopes to combine some rationality with some freedom in this model, so both determinists and libertarians can accept it. He says that although the two-stage model of earlier thinkers is an "essential and important part" of any adequate libertarian conception of free will, it does not go far enough because it does not fully capture the notion of ultimate responsibility (Kane's UR) during rare "self-forming actions (SFAs). It is merely a "significant piece in the overall puzzle of a libertarian freedom."[17]

"The reason is that the chance ("free") part is not in the control of the agent and the "will" part is fully determined by a combination of the chance part and other determining factors, so the final choice is determined by factors, none of which the agent has control over at the time of choice. If all of our choices are determined at the time of choice that would not be libertarian freedom even if some chance events in the past were responsible for forming some of the determining factors that now determine our choice because however the determining factors were formed in the past, all of our choices would be determined when they are made." (personal communication) [18]

Kane wants what he calls "dual rational control", which is the ability to choose otherwise in exactly the same circumstances. He argues that this requires some randomness in the decision itself. But the randomness does not compromise the agent's responsibility, if the agent has justifiable reasons for choosing either way.

Kane has thus reconciled chance with responsibility in what he and colleagues call "torn decisions."

David Sedley and Anthony Long[edit]

David Sedley and Anthony Long speculated in their 1987 masterwork The Hellenistic Philosophers that Epicurus's swerve of the atoms might be limited to providing undetermined alternative possibilities for action, from which the mind's power of volition could choose in a way that reflects character and values, desires and feelings.

Here at last a significant role for the swerve leaps to the eye. For it is to answer just this question, according to Cicero, that the swerve was introduced. The evident power of the self and its volitions to intervene in the physical processes of soul and body would be inexplicable if physical laws alone were sufficient to determine the precise trajectory of every atom. Therefore physical laws are not sufficient to determine the precise trajectory of every atom. There is a minimal degree of physical indeterminism — the swerve. An unimpeded atom may at any given moment continue its present trajectory, but equally may 'swerve' into one of the adjacent parallel trajectories.

As far as physics is concerned there is simply no reason for its following one rather than another of these trajectories. Normally, then, the result will be, in this minimal degree, random. But in the special case of the mind there is also a non-physical cause, volition, which can affect the atoms of which it is a property.

Sedley and Long assume a non-physical (metaphysical) ability of the volition to affect the atoms, which is implausible. But the idea that a physical volition chooses - (consistent with and adequately determined by the agent's character and values and its desires and feelings) from among alternative possibilities provided randomly by the atoms - is quite plausible.

It does so, we may speculate, not by overriding the laws of physics, but by choosing between the alternative possibilities which the laws of physics leave open. In this way a large group of soul atoms might simultaneously be diverted into a new pattern of motion, and thus radically redirect the motion of the body. Such an event, requiring as it does the coincidence of numerous swerves, would be statistically most improbable according to the laws of physics alone. But it is still, on the swerve theory, an intrinsically possible one, which volition might therefore be held to bring about. For a very similar thesis relating free will to modern quantum indeterminism, see A. S. Eddington, The nature of the physical world (1928). (It may be objected that swerves are meant to be entirely uncaused; but, as E 2 shows, that was only an inference by Epicurus' critics, made plausible by concentrating on the swerve's cosmogonic function, cf. 11H, for there it must indeed occur at random and without the intervention of volition.)[19]

Given today's quantum mechanical indeterminacy, Epicurus's intuition of a fundamental randomness in nature was correct. But he did not think the swerves were the direct causes of our actions. He agreed with Aristotle that beyond necessity (άνάyκη) and chance (τυχῆ), there is a third kind of basic cause - agent causes that are "up to us" (ἐφ' ἡμῖν or παρ’ ῆμᾶς). How exactly determinism and chance relate to autonomous agent causality is not made clear, but Aristotle and Epicurus should be classed today as "agent-causal libertarians."

Alfred Mele[edit]

In 1995 Alfred Mele, clearly influenced by Daniel Dennett and Robert Kane, proposed his "Modest Libertarianism", a two-stage process that combines an incompatibilist early phase followed by a compatibilist control phase. He made it clear, following Dennett's "Valerian" model in Brainstorms, 1978, that the indeterminism should come early in the overall process. He even describes the latter - decision - part of the process as compatibilist (effectively determinist). This of course could only be adequate determinism.

it might be worth exploring the possibility of combining a compatibilist conception of the later parts of a process issuing in full blown, deliberative, intentional action with an incompatibilist conception of the earlier parts. For example, it might be possible to gain "ultimate control" while preserving a considerable measure of nonultimate agential control by treating the process from proximal decisive better judgment through overt action in a compatibilist way and finding a theoretically useful place for indeterminacy in processes leading to proximal decisive better judgments[20]

Mele sees that chance need not be the direct cause of action.

That a consideration is indeterministically caused to come to mind does not entail that the agent has no control over how he responds to it [21]

Mele is very concerned about the location of any indeterminism, the problem of where and when indeterminism could occur in a way that helps and does not harm agent control.

The Problem of Luck

Mele has written extensively about the question whether chance events in our causal history mean that many of our actions are a matter of luck. Since chance is very real, many things are the result of good or bad luck. This is a not a problem for free will, but it is one for moral responsibility.

Bob Doyle[edit]

Bob Doyle, a philosopher who initially became an astrophysicist to investigate indeterminism at the deepest level in the universe, is a passionate advocate for the two-stage model and has done much to promote it amongst philosophers in recent years. He has spent many years studying the history of free will and was the first to recognise William James as the earliest philosopher to formally propose the two-stage model.

Doyle has publishes a website called the information philosopher, which outlines the views of over 130 philosophers and over 60 physicists on the subject of free will, its history and the rise of the two-stage model. The site also provides background to Doyle's own theory of information (in a technical sense as a certain kind of negative entropy) as a key principle underlying the chance part of the two-stage model. While the two-stage model supports both determinists and indeterminists, Doyle's detailed work in quantum indeterminacy offers a strong steer to the latter.

Martin Heisenberg[edit]

The most recent thinker to describe a two-stage model is Martin Heisenberg (son of physicist Werner Heisenberg), chair of the University of Würzburg's BioZentrum genetics and neurobiology section.

Since the Uncertainty principle was his father's work, Heisenberg's position that the physical universe is no longer determined and that nature is inherently unpredictable comes as no surprise. What is unusual is that Heisenberg finds evidence of free behavior in animals, including some very simple ones such as Drosophila, on which he is a world expert. Heisenberg argues for some randomness even in unicellular bacteria, followed by more lawful behaviors such as moving toward food.

Evidence of randomly generated action — action that is distinct from reaction because it does not depend upon external stimuli — can be found in unicellular organisms. Take the way the bacterium Escherichia coli moves. It has a flagellum that can rotate around its longitudinal axis in either direction: one way drives the bacterium forward, the other causes it to tumble at random so that it ends up facing in a new direction ready for the next phase of forward motion. This 'random walk' can be modulated by sensory receptors, enabling the bacterium to find food and the right temperature.[22]

In higher organisms, the brain still may include elements that do a random walk among options for action. The capability to generate new and unpredictable behaviors would have great survival value, and would likely be incorporated in higher organisms.

the activation of behavioural modules is based on the interplay between chance and lawfulness in the brain. Insufficiently equipped, insufficiently informed and short of time, animals have to find a module that is adaptive. Their brains, in a kind of random walk, continuously preactivate, discard and reconfigure their options, and evaluate their possible short-term and long-term consequences.

The physiology of how this happens has been little investigated. But there is plenty of evidence that an animal's behaviour cannot be reduced to responses. For example, my lab has demonstrated that fruit flies, in situations they have never encountered, can modify their expectations about the consequences of their actions. They can solve problems that no individual fly in the evolutionary history of the species has solved before. Our experiments show that they actively initiate behaviour.[23]

Heisenberg's combination of some randomness followed by some "lawful" behavior looks very much like William James’ two-stage model for human freedom, but now there is evidence for behavioral freedom in even the lowest animals.


  1. ^ Ernst Mayr, Toward a New Philosophy of Biology, Harvard, 1988, p.150.
  2. ^ Martin Heisenberg, "Is Free Will an Illusion?", Nature, 459, (May 2009): 164-165.
  3. ^ William James, "The Dilemma of Determinism", The Will to Believe (New York, Dover, 1956), p. 145
  4. ^ William James, "Great Men, Great Thoughts, and the Environment", Atlantic Monthly 46 (October 1880): 441-459.
  5. ^ Henri Poincaré, Science and Method, chapter 3, "Mathematical Discovery", 1914, pp.58
  6. ^ A. H. Compton, Science, 74, 1911, August 14, 1931
  7. ^ Arthur Holly Compton, The Cosmos of Arthur Holly Compton, 1967.
  8. ^ Karl Popper, Objective Knowledge, "Of Clouds and Clocks", 1972, p. 232
  9. ^ Karl Popper and John Eccles, The Self and Its Brain, p.540
  10. ^ Cf. Objective Knowledge, chapter 6, pp. 226-29.
  11. ^ See p. 540 of The Self and Its Brain
  12. ^ Delivered at Darwin College, Cambridge, UK, November 8, 1977(A shortened version is available as an audio recording.)
  13. ^ Lawrence LeShan and Henry Margenau, Einstein's Space and Van Gogh's Sky, p.240
  14. ^ Daniel Dennett, "On Giving Libertarians What They Say They Want", Brainstorms, 1978, p.295-7
  15. ^ Robert Kane, Free Will and Values, p.165
  16. ^ Robert Kane, Free Will and Values, p.96
  17. ^ Robert Kane, Free Will and Values, p.104
  18. ^ Bob Doyle, personal communication from Bob Kane
  19. ^ David Sedley and Anthony Long, The Hellenistic Philosophers, vol. 1, section 20, Free Will, p.110-111
  20. ^ Alfred Mele, Autonomous Agents, p.212.
  21. ^ Alfred Mele, Free Will and Luck, p.10
  22. ^ Martin Heisenberg, "Is Free Will an Illusion?", Nature, 459, (May 2009): 164-165
  23. ^ ibid., p.165