There seems to be no logical link between matter and determinism (or ideal and indeterminism for that matter). And libertarian free will was first articulated by a materialist, Epicurus, and is defended at length in Lucretius's famous poem. The reasoning was interesting, too. Man is free. Man is made of atoms. Therefore, atoms swerve. Not a bad prediction about physics.

But in modern times materialists, starting with Spinoza, tended to reverse the logic. Atoms do not swerve ("God doesn't play dice"). Man is made of atoms. Therefore, man is not free. In fact, man is not free even if atoms do swerve. This is Dennett's idea of "giving libertarians what they say they want". Most libertarians were and are idealists or dualists. Contemporary libertarian materialists are few, but notably Kane and Searle.

This is understandable to me for the times of classical physics, which strongly suggested determinism. But if classical physics was such a strong argument for determinism why not take modern physics at face value. Why try to explain it away? Rather than reinterpret physics to conform with apparent facts, like Epicurus, or reinterpret facts to conform with physics, like mechanical materialists, contemporary compatibilists choose to reinterpret both, physics and facts, to conform with determinism, perhaps diluted by "chance". This is a thin rope to walk. Kant once braved it to do the opposite, to make room for free will. The tables have turned.

This must mean that determinism in and of itself must hold a strong appeal for materialists (and perhaps others), perhaps an instinctive one, enough to overcome the apparent intuition to the contrary. Where does it come from? What are the arguments for it? Why is libertarian materialism so unpopular?

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    I don't know if Searle is really a materialist - or (here we go again) is non reductive materialism any different from dualism? Commented Dec 14, 2015 at 23:25
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    Also - most "lay" materialists I know (as in every day atheists who have studied little or no philosophy) are actually libertarian freewillers , who see themselves as being free compared to theists who they see as puppets to divine predestination. Commented Dec 14, 2015 at 23:29
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    @Alexander S King I just take them at their word. Davidson and Searle are both non-reductive materialists, but Davidson self-identifies as compatibilist and Searle as libertarian. I've seen Dennett accused of covert libertarianism, and truth be told except for quantum talk I can see little difference between his model of free will and James's. But truth be told I have doubts that James's model itself is libertarian, despite his self-identification. It may be that at this point models are too crude to capture author's intent. Kane complains that his own doesn't, and maybe no model can.
    – Conifold
    Commented Dec 15, 2015 at 1:37
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    At one point in this interview, either Dennett himself suggests (or the interviewer suggests and Dennett concurs - I forget which and can't go back and check now) that Freewill is a emergent property (like macroscopic color). Sounds like a closeted libertarian to me. Commented Dec 15, 2015 at 1:47
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    @Alexander S King Nah, he just means it in the same sense that sand dunes are emergent on sand grains, or Siri is emergent on arrays of 0-1s. If we can not count on Dennett to reduce it all down to firing neurons who can we count on :)
    – Conifold
    Commented Dec 15, 2015 at 2:15

4 Answers 4


I tend to share your puzzlement. A lot of contemporary metaphysicians seem to have an outdated view of physics, not only about determinism but also about locality or mereology. (This was criticized by Ladyman and Ross in "everything must go".)

I think the main reasons are the following:

  • Generally, philosophers are not trained in physics (except philosophers of physics) so they don't feel confident using too many technical aspects from modern physics in their arguments. They would rather rely on the philosophical tradition for their metaphysics, and on an intuitive picture of matter. This is only worsened by the fact that contemporary physics is very complex and mathematical, and that academic fields are more and more specialized.

  • Quantum physics is counter-intuitive and not well understood at a conceptual level. There is no real consensus on the metaphysical interpretation. Maybe they think that using quantum physics will bring up more problems than solutions and they prefer to rely on a well understood physics, while waiting for a consensus to emerge in the philosophy of physics on the right metaphysical picture to adopt. Some would even think that the central aspects of quantum physics are deeply problematic, and will eventually disappear in future theories (which demonstrates a lack of knowledge of these issues, I think).

  • In any case quantum physics is not relevant because it only applies at microscopic levels. Classical physics (hence determinism) is true for all practical purposes at the level of human beings (which is the level of interest when it comes to freewill). So it's not really a problem to reason in a classical framework for philosophical arguments on freewill. More sophisticated version: decoherence implies that quantum effects are irrelevant in human behaviour, and even in microbiology, so we can ignore them (this is not completely true).

  • Randomness is not the same as freewill anyway. To the contrary, agency requires determinism: if actions are random, they are not free. Even more so if randomness is the result of many incoherent microscopic fluctuations: that's only determinism + noise. So again, we can reason in a deterministic framework and just ignore the noise.

  • There are also more metaphysical motivations for determinism, such as the view that everything must occur for a reason, that all phenomena must have a physical explanation, that all events must have a complete cause, and that indeterminism must result from an incompleteness of our knowledge.

Personally I don't think any of these reasons are good (although some are not so easily rejected) and we can discuss that in comments if you want.

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    Agree fully on the dated view, many many writings on quantum philosophy give me a distinct impression that their authors do think of electrons as something like swerving atoms. Tegmark's "brain is to warm, wet and noisy" also left a deep mark, especially on those who are glad to have a respectable excuse to look no further, Zurek's review shows how simplistic that is arxiv.org/abs/quant-ph/9802054. But is inertia really all there is to it? I often get a feeling that people are passionate about "God doesn't play dice" (or "chance is the only alternative"), like Einstein was, not inertial
    – Conifold
    Commented Dec 15, 2015 at 2:03
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    @Conifold yes certainly, I would classify it in the fourth point in my answer. Perhaps it would deserve more analysis. Now having discussed with a few philosophers of mind or metaphysician, I can tell you that for most of them, quantum mechanics is really foreign to how they think about the "physical". They don't have a clear view of the central aspects of QM (the measurement problem, non locality, contextually) or only superficially, and they tend to view it as microscopic weirdness they don't have to bother about. I heard it quite explicitly several times. Commented Dec 15, 2015 at 12:37
  • @Conifold I meant the fifth (last) point. Commented Dec 15, 2015 at 13:18

Materialism and determinism are indeed, I think, closely linked, in the following way:

  1. The main attraction of materialism is the ability of material theories to causally explain vast areas of phenomena.

  2. An adequate causal explanation by a material theory implies an instance of determinism. Because it consists in a phenomenon completely derived from material conditions and antecedents. And this implies, in particular, that no free will is required in the explanation.

Therefore, materialism and determinism go hand in hand, not because they inherently imply each other, but because one of them (determinism) is implied by the motivation and by the justification of the other (materialism).

The deviation of QM from strict determinism is a source of embarrassment to the determinist. Yet, several factors lessen this embarrassment. First, those deviations from determinism are limited and circumscribed. Second, the deviations not seem related to anything resembling free will. Third, computationally speaking, QM is the most "deterministic" material theory to date, in the sense that it provides the most precise predictions.

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    Very interesting points. But why does adequate materialistic explanation have to be causal? Epicurus did not seem to take it that way, he explains both man and cosmogony by in-determinism. And conversely, causal action at a distance had little explanatory power and was seen as ghostly. Quantum deviations seem to be directly related to free will, they remove the determinism/chance false dichotomy, provide ontological furniture that free will requires, essentially validating Epicurean prediction, and serving as a centerpiece in all free will models, even Dennett’s.
    – Conifold
    Commented Dec 16, 2015 at 1:17
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    @coni It could be my ignorance, but I don't see any relevant connection between quantum deviations and free will.. Commented Dec 16, 2015 at 17:55

Determinism is derived almost directly from assuming causation. Free will is derived from experienced phenomenology. The free will experience contradicts the theory of causation, just as with consciousness and reductionism.

When one prioritizes theory over experience, one will arrive at reductionist materialism, and determinism. When one prioritizes experience over theory, one will arrive at the reality of consciousness, and free will.

This is why materialists are determinists, and dualists/idealists are libertarians -- the epistemologies line up.

  • Determinism does not follow from causation, straightforwardly or otherwise. Quantum mechanics is an example of indeterministic (probabilistic) causation. And even when one prioritizes theory over experience one can arrive at many places aside from reductive materialism, say empiricism, idealism, etc.
    – Conifold
    Commented Oct 31, 2017 at 22:36
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    Every determinist I have read says they are determinists because they believe in reasons for events -- I.E a straight derivation from causation. Yes, there are other possible combinations, but they don't come with such naturally shared epistemologies. When Idealism was more common, there was a lot of reason-based idealism (rather than the psychological idealism of today), which lines up naturally with determinism.
    – Dcleve
    Commented Nov 2, 2017 at 3:43
  • Citations needed!
    – viuser
    Commented Nov 2, 2017 at 9:07
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    What do you want citations for wolf-revo-cats?
    – Dcleve
    Commented Nov 3, 2017 at 22:34

"Why is libertarian materialism so unpopular?"

It is because it seems "subjective".

If one looks at the difficulties involved in a serious-minded manner, one sees that almost no one who speaks about the issue has a proper sense of what they are talking about. It's simply an irrational bias which sides this way or that way.

The fact that mathematical objects, such as forces, are said to be either determined or probabilistic, is without meaning for actual life, and can not be held up as a higher judge against personal views. It is not a scientific question. Science, as it stands, simply makes things work, e.g., an fMRI machine, or it doesn't. Its theory is not based on human guidance (so far as it is properly scientific, i.e., objective), but a stock of blind working instructions.

The question is very much like the issue with artificial intelligence. Science is a typewriter, as Alan Turing (against what one might imagine, given the way he is used) said: it is a question too stupid to be taken seriously, concerning whether a machine can be aware of itself. If one really thinks about it, science has nothing to say about such issues.

The question arises from the fact that the authority of the sciences pours out, like an infection, into the sphere of public punditry. This is true even if we mean the discussion between men of a stature no longer seen, such as Einstein and Heisenberg. Their competency was limited to the mathematical models. What they said beyond that was personal opinion.

  • This might explain it for general public (if it cared about philosophy), but how would public punditry affect academic philosophers? I also do not see how determinism or indeterminism have anything to do with subjectivity.
    – Conifold
    Commented Nov 2, 2017 at 0:39
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    "academic philosophers" Because they too are effected by general biases. The biases of their epoch, e.g., the Enlightenment. " I also do not see how determinism or indeterminism have anything to do with subjectivity." Determinism has to mean the objectified object, that is, not the object for common sense, but something held to exist independently of the human being, which requires no human representation. Otherwise one would have to speak of anthropomorphic notions of Fate, or some such un-scientific, ergo, in the widest sense un-objective, view. Commented Nov 4, 2017 at 22:09

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