I've seen similar questions asked once or twice on here, but I wasn't able to find a satisfying defense of libertarian free will. The answers seemed to be kind of scattered. So, I wanted to make clear terms, definitions and place the argument in a syllogism.


  • Determined action: an action on the causal chain which is fully determined by the previous state of the causal chain
  • Random action: an action on the causal chain that is not determined to any degree by the previous state of the causal chain
  • Probabilistic action: an action on the causal chain that is partially determined by the previous state of the causal chain
  • Agent: any entity capable of choice. I'm intentionally vague here so that agent would include someone who has libertarian free will or determined choices (like AI choices)


  • All actions are part of the casual chain. (This does not exclude non-determined actions. Imagine that we created a true RNG. It's output would be on the causal chain, but what number comes out would not be determined by the previous state of the causal chain.)
  • There are no casual loops


  • When random, determined and probabilistic are mentioned, I'm speaking ontologically, not epistemically. So, it only matters if something is actually random; it doesn't matter if we cannot tell whether or not it is random.


  • Premise 1: All actions are ultimately either random, determined, or probabilistic actions.
  • Premise 2: Agents that only make ultimately random, determined, or probabilistic actions are not ultimately responsible for their actions.
  • Conclusion: Agents are not ultimately responsible for their actions.

I'm specifically seeking a definition for libertarian freewill in terms of how it exists on the causal chain. I've seen the term "agent-causation", but have been able to find a definition for it (as how it would exist on the causal chain).

  • 4
    An action that is partially determined need not follow any probability distribution, it can just be constrained in some way (by physical laws, intentions, etc.). So Premise 1 is false. For theories of agent causation see SEP. In a nutshell, "an agent is in a strict and literal sense an originator of her free decisions, an uncaused cause of them". For models of free will that involve agent causation see Information Philosopher.
    – Conifold
    Commented Jan 21, 2023 at 9:07
  • 1
    Is randomness equal to when the previous stage does not determine the succeeding stage? I think I've seen a description of pi such that it is considered random, in a sense, which digit comes next in its decimal expansion, yet it is also determined which digit is which, wherever each digit is. I mean, it's not sequential in the repeating manner, which might be the baseline "intuitive" manner. But it's still functionally determinable. So it is said that chance and randomness differ: it's random that 3.14... is pi's decimal expansion, but there's a 100% chance that each digit is what it is. Commented Jan 21, 2023 at 13:53
  • Premise 1) is not the whole story. Actions can be completely determined, completely random, or under the agents control (partially determined or random). Even if one accepts premise 1) in general, it does not forbid agent causation. If the universe can create true randomness, there is no reason agents cannot share this physical ability as parts of the universe, sharing physical principles of the universe. Claiming otherwise is begging the question
    – Nikos M.
    Commented Jan 21, 2023 at 17:12
  • 1
    You may be interested in this post about ultimate responsibility.
    – Nikos M.
    Commented Jan 21, 2023 at 18:28

2 Answers 2


The causal chain is not a necessary property of all philosophic stances. So some libertarians may reject your presupposition. And hence also your premise 1.

If you first define the world in a way that makes libertarian free will impossible, then you will find that your conclusion will be that libertarian free will is impossible.

To give an example of how libertarians could justify their views: the brain could be an antenna for the mind, with the mind residing in another plane of existence, where there is no time, or time is not linear, and so causation just works differently where the mind is. Three brain could steer the body as directed by the mind without necessarily violating physics, if the mind uses the loophole of "quantum motion" to influence the brain processes that cause human action. So what looks like probabilistic/random subatomic events to scientist today could be the mind at work.

This is just an example of how a libertarian could try to consolidate free will with observable laws of physical reality (they don't have to, they can just refuse to accept the chain of causality without providing a viable alternative).

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    Love the example! That is just what I was looking for. However, to address "The causal chain is not a necessary property of all philosophic stances. So some libertarians may reject your presupposition. And hence also your premise 1." Perhaps my use of the term "causal chain" is misleading. I probably should have used "causal space". Meaning that everything event has a cause. The first event(s) would be caused by necessity. Wouldn't something not being in causal space be the same as being the way it is for no reason (ie random)? Or am I missing a step? Commented Jan 21, 2023 at 23:57

I would like to challenge your terms. They are slightly misleading.

  • Determined action: Nothing in reality is completely determined by the previous causal state. Causes never determine their effects with absolute accuracy.
  • Random action: In reality, there are no such events at all that are completely undetermined either. In the philosophical context I use the word random in the meaning of unintentional or purposeless. Randomness does not mean the absence of causality, it means the absence of teleology.
  • Probabilistic action: Every event and action in reality is probabilistic, only partially determined by the cause.
  • Agent: An entity capable of starting new causal chains of events.

Agent-causation means that the cause for an action is not the previous event, but instead a decision made by the agent. Therefore agent-causation is practically the same thing as free will. There may be philosophical nuances, but for a layman they mean the same.

Libertarian free will means free will in the absence of determinism as opposed to compatibilism, which means free will somehow compatible with determinism. Since there is no determinism in reality, we can forget both compatibilism and the prefix "libertarian". There is only one kind of free will and that is agent-causation.

  • The answer can be improved by decoupling ontic from epistemic notions of uncertainty.
    – Nikos M.
    Commented Jan 21, 2023 at 18:23
  • What reasons would there be for rejecting the possibility of fully determined or fully random actions? Commented Jan 22, 2023 at 0:03
  • I'm not sure that I follow your distinction between in your definition of agent. If the agent exists for a reason (s), then the agent is on the causal chain. If they then initiate some action, then that action would be on the same casual chain, right? Then if it's on the same casual chain, the action produced would be either determined, random, or probabilistic. Commented Jan 22, 2023 at 0:06
  • @ZacharyBohn Fully determined and fully random actions as you define them simply don't happen ever. They are not part of reality, they are useless theoretical ideas. Well, you could say that the Big Bang was a fully random event as there was no cause before it, but that is not relevant. Commented Jan 22, 2023 at 5:19
  • @ZacharyBohn Our definitions for agent are not that much different. I see making a choice as essentially the same thing as starting a new causal chain of events. You seem to think that there is only one causal chain. That is not the case. Choices cannot be caused, as choices are not physical events, choices are knowledge about future actions. But choices do cause physical actions, the agent's choices cause the agent's actions without being caused themselves. Commented Jan 22, 2023 at 5:26

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