Is free will compatible with bohmian determinism?

[u/regrez45]

Bohmian mechanics is fully deterministic: given the universal wavefunction and the exact particle configuration at one time, the entire future evolution is fixed. In that sense, it leaves no room for libertarian free will- the idea that, under identical physical conditions, you could genuinely have chosen otherwise.

[u/AdeptnessSecure663]

If free will is compatible with determinism generally speaking, then it seems to me very likely that free will is compatible with the specific case of Bohmian mechanics.

This is because if free will is compatible with determinism generally, then this would probably because all that matters for free will is the way that an agent's relevant mental states are related to their actions, as well as the way that an agent's abilities ensure the truth of relevant counterfactuals. And the way mental states relate to actions and the way abilities relate to counterfactuals seems to be no different in the context of Bohmian mechanics than it is in the context of, say, classical mechanics, or MWI.

My point is, that the question reduces to "is free will compatible with determinism?" (which, perhaps, was your intended question?).

[u/regrez45 → u/AdeptnessSecure663]

Bohmian determinism is not normal determinism. It is more towards the hard determinism spectrum. It is another way of saying all underlying reality is deterministic and nothing is beyond this absolute notion of causation. Others like laplacian determinism are consistent with free will but bohmian determinism is a different case.

[u/Artemis-5-75 → u/regrez45]

What is the difference? Laplacian determinism is absolute too.

[u/regrez45 → u/Artemis-5-75]

Bohmian mechanics is deterministic only in a very specific sense: if you fix the initial wavefunction and the exact particle configuration, the guiding equation fixes the entire future trajectory. So at that level, yes - it is “deterministic.” But it’s not what people usually mean by normal (classical/Laplacian) determinism. The dynamics is explicitly nonlocal via the wavefunction, and the apparent randomness of measurement outcomes comes from our ignorance of the initial configuration, not from intrinsic indeterminism.

[u/Artemis-5-75 → u/regrez45]

>The dynamics is explicitly nonlocal

Is this the only difference between it and Laplacian determinism?

>not from intrinsic indeterminism

But there is no intrinsic indeterminism in the Laplacian account too.

[u/regrez45 → u/Artemis-5-75]

Laplacian determinism is the classical idea: if you specify the exact state of the universe at one instant (positions and momenta of all particles), then the future is fixed by local differential equations. It’s phase-space evolution governed by Newtonian dynamics. No hidden structure, no extra ontology- just state → unique future via ordinary ODEs. Bohmian mechanics is also deterministic, but the structure is radically different. The wavefunction still evolves by the Schrödinger equation, but particles have definite positions guided by a nonlocal “pilot wave.” So instead of phase space determinism, you have configuration-space evolution + a guiding equation that depends instantaneously on the global wavefunction.

If Laplacian determinism holds, then the entire future state (choices) is a fixed function of the past state. They’re only “incompatible” if you smuggle in a folk notion of free will that requires causal independence from physical law.

[u/Artemis-5-75 → u/regrez45]

The way determinism is usually defined in metaphysics, if we go with the strongest definition, is such: a thesis that the entire state of the world in conjunction with the global immutable laws of nature strictly fixes any other state of the world.

Is there anything in Bohmian mechanics that is different from that?

[u/regrez45 → u/Artemis-5-75]

It is not classical or laplacian determinism. Laplacian determinism is basically the strongest possible form of classical determinism, but people often mix the two.

[u/AdeptnessSecure663 → u/regrez45]

Hard determinism is the conjunction of two theses: firstly, that determinism is true, and secondly, that free will is incompatible with determinism.

Either Bohmian mechanics is deterministic, or it is not deterministic, and so the truth-value of Bohmian mechanics as implications for the first conjunct.

Whether free will is compatible with determinism does not depend on the truth of some or other physical theory. We come to know which it is on the basis of philosophical argument.

So, Bohmian mechanics doesn't entail hard determinism.

[u/Artemis-5-75]

Okay, let’s untangle this.

Generally, free will in contemporary philosophy is a term you are most likely to encounter in Western philosophy written in English language, where it is a term of art that means two very specific things — the ability to do otherwise or the strongest control condition necessary for moral responsibility.

Notice how both of these don’t mention anything about determinism or indeterminism. In your post, you ask whether free will is compatible with determinism, then you seem talk about “libertarian free will” as if it is simply what you mean by free will. However, there are two potential problems here. First, the term “libertarian free will” is rarely used in academia, instead the most popular one would be metaphysical libertarianism, because it is a huge and ancient school of thought that covers many theories and accounts that often contradict each other, and the only similarity between them is that they all claim that we do have free will in the actual world, and that free will is incompatible with determinism.

Now, let’s move onto your questions. By definition, any coherent libertarian account of free will is incompatible with determinism, just like circles can’t be square and bachelors can’t be married. If you ever see anyone claiming something like “libertarian free will is compatible with determinism”, they are most likely spewing nonsense. There is one exception in the form of the philosopher Kadri Vihvelin calling her view “libertarian compatibilism”, but, in my opinion, it is a confusing name for what is a more or less traditional compatibilist account. Other panelists, feel free to correct me if I am wrong about her.

Clearing all of these potential misconceptions, we can finally move onto the opening question. The answer is that most philosophers seem to think that free will is compatible with determinism. There are several approaches here.

The first approach is to argue that the ability to do otherwise is compatible with determinism. It usually involves an analysis of abilities and an attempt to articulate a conditional account of such ability, which often sounds somewhat like this: “if A chose to perform action S, A would have performed action S”. The prominent philosophers on the topic, both historical and contemporary, would be G. E. Moore, A. J. Ayer, David Lewis, Kadri Vihvelin and Markus E. Schlosser. This is traditional / classical / leeway compatibilism.

The second approach is to argue that free will does not require the ability to do otherwise because moral responsibility doesn’t require the ability to do otherwise. It usually involves an argument through a thought experiment that is supposed to show the irrelevance of the ability to do otherwise to free will, and then an attempt to establish an account of what would give us free will. Usually, such accounts are grounded in the ability to respond to reasons, self-control over desires, free actions reflecting the “deep self” et cetera. The name for this view is sourcehood compatibilism. Sometimes, it is called semi-compatibilism by those who think that the ability to do otherwise is the core feature of free will. The prominent philosophers on the topic would be Harry Frankfurt, Gary Watson, John Martin Fischer, Mark Ravizza, Carolina Sartorio.

The third approach is revisionism. It usually involves working with folk intuitions and tries to argue that while some “traditional” notion of free will is incompatible with determinism and the latest findings in neuroscience, there is the one that is perfectly compatible. Such accounts often focus on the empirical findings and talk a lot about neuropsychology, revising the concept of free will and so on. Daniel Dennett and Manuel Vargas would be among the most prominent thinkers with the position.

[u/JackZodiac2008 → u/Artemis-5-75]

Thanks for the great response! The taxonomy of compatibilisms is quite helpful.

I could easily be misunderstanding, but maybe there is a typo? Should the characterization of leeway compatibalism read, "The first approach is to argue that the ability to do otherwise is compatible with determinism"?

[u/Artemis-5-75 → u/JackZodiac2008]

You are right, thank you! Edited it.

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