So let's assume that free will requires the ability to have done the opposite.

Suppose we abstract from the world (and from our mind) and can reproduce an event in the same conditions as given including exact time and space (and exact mental states).

Also suppose it is an event in which the possibility of doing the opposite is a preference choice, such as choosing between two flavors of ice cream that you like.

So the question is the following: When reproducing this event, is there a world in which, for example, we could have chosen another flavor of ice cream?

If so, what causes this change?


2 Answers 2


When reproducing this event, is there a world in which, for example, we could have chosen another flavor of ice cream?

It's an article of metaphysical presumption, but for most philosophers, intuitions lead to the answer of yes, there is another world. Such a world today is referred to as a 'possible world', and today the language is used widely to denote the domain of discourse in which counterfactuals and hypotheticals exist sometimes with existence being taken not as an abstract object (SEP) but as in physically real such as the modal realism espoused by Lewis and others.

It should be noted that one doesn't have to admit possible worlds as anything other than abstract objects, meaning that there are philosophies that would reject the notion that anything other than what did happen could happen in a metaphysical sense, and that the use of language to speculate has no bearing on determining physical reality thusly rejecting mental causation. But certainly, it is an intuitive approach to believe that our choices do determine physical reality.

what causes this change?

This is simply an extremely open question with no canonical answer. If you accept mental causation, then we do. If you reject mental causation, then our brains do. If you take some muddled and middle approach, our minds and brains do. What is important to know that this is very much an open question in philosophy of mind, because of contemporary philosophies, there are radically different perspectives from those of the eliminative materialists to those of cognitive scientists to those of phenomenologists and existentialists. One's philosophical framework and metaphysical presuppositions strongly determine one's answer to this question, and you'll find less and less agreement the more detailed the response you find. Ultimately, you're going to have to answer this question yourself.

  • Could we represent both possible worlds as models? in which in one model a certain flavor of ice cream was chosen and in another model a different flavor was chosen. What I want to know more specifically is: if we start from a model prior to those two models that I have just mentioned, is it possible that (to put it in some way) let time run and obtain two different models from the same previous model? Just letting time pass. Mar 27, 2023 at 16:05
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    Can we model possible worlds? Absolutely. Possible worlds as abstract objects are used in AI when modeling problem spaces. Poole and Mackworth's textbook repeatedly invoke possible world semantics when building various AI systems which to me is just an endorsement that natural language semantics serves the same function in human thought that it does in the artificial forms.
    – J D
    Mar 27, 2023 at 19:02

There is a significant number of people who reject compatibilism (the idea that determinism and free will is compatible). If compatibilism is false, given a deterministic universe, this would imply that free will doesn't exist. But we don't even need to suppose a deterministic universe to reject the concept of free will.

I would argue that the idea of free will is a thoroughly dead concept, that simply doesn't make sense given our modern understanding of reality, causality and the brain. At this point, it's merely a nice idea, that seems important, without any remaining rational grounding.

Let's suppose we can reproduce a state of the universe down to the last atom, boson and whatever else. If someone is given a choice and they act differently the second time around, this would imply one of the following:

  • They have some existence outside of the universe. This does little more than introduce something we didn't reproduce (that we also don't have compelling evidence for), rather than actually solving the problem. To address this, we can simply extend the hypothetical to suppose that we also exactly reproduced any existence external to the universe.

  • Their actions have some random element. This may meet the requirements of the problem, but acting randomly does not match what we think of as "free will". We certainly wouldn't call a random number generator "free".

I do not see any other option.

Something is either deterministic or random. If it's deterministic, it would be the same every time we reproduce it. If it's random, it's not "free".

Barring randomness, if we reproduced them exactly, with every desire and thought process that they had at that point in time, and we put them in the exact same situation, they should weigh up the available choices in the same way based on their identical desires, and end up making the same choice.

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    You are making strong statements about free will without defining what you mean by it. You seem to follow the definition mentioned in the question, but as that one is an invalid and illogical definition, your answer is equally invalid and illogical. There can never be any "second time around". It is quite pointless to speculate on the impossible. That says nothing about what is possible or real. Mar 29, 2023 at 10:08
  • @PerttiRuismäki I'm following the definition of "free will" used in the question and that's commonly used in philosophy (which I do agree is illogical: that literally what my answer is saying). Philosophy involves a whole lot of speculation of hypotheticals that may or may not be possible, so it seems misguided to take issue with this fact on an answer on a philosophy Q&A. And it is not "quite pointless" to hypothesise regarding free will, as this may tell us that actions are determined by circumstances, which could lead us to redefine our entire justice system, at least.
    – NotThatGuy
    Mar 29, 2023 at 10:19
  • If the definition is invalid and illogical it should be rejected altogether as it is empirically untestable and any philosophical thought experiments will give only invalid and illogical results. A proper definition of free will says clearly whether it is a real phenomenon or an imaginary idea. Our actions are not determined by circumstances (except for spinal reflexes, they are). Whatever it is that you choose to call "free will", there will be no need to redefine justice system. Mar 29, 2023 at 11:33
  • @PerttiRuismäki It's curious that (as per your profile) 2 of the 3 of your "main areas of interest in philosophy" is determinism and free will, and yet you object so strongly to anyone using the definition of free will that's accepted in philosophy, and you seem to not be aware of any possible consequence that a lack of free will will have for how we think of justice. I might recommend some formal education in philosophy, where you should be exposed to some of these ideas and where I'd hope you'd be less confrontational and more open towards exploring such ideas.
    – NotThatGuy
    Mar 29, 2023 at 11:50
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    @PerttiRuismäki "It is quite pointless to speculate on the impossible." You should have told Einstein that before he did it with his Gedankspiel about sitting on a lightbeam to help him invent the theories of general and special relativity. It's a brute fact that people routinely speculate on the possible and impossible to determine what is possible and bring the design to production, and that no one operates free of modal speculation in practice. The last clause, in fact, is a psychological truth.
    – J D
    Mar 29, 2023 at 16:42

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