The phrase "could have done otherwise" is almost essential to all discussions concerning free will. Most philosophers, as I understand the literature, believe this phrase characterizes and validates moral responsibility. My question relates to how one can make sense of this phrase in the context of libertarian free will.

Consider a choice C that a free agent A makes at t. In some sense, under libertarian free will, until t, the outcome of C is not decided. Instead, there are possible outcomes after t, meaning that it is both logically possible before t that at t A chooses C1 or C2. Now, suppose A chooses C1 at t. A could have chosen differently, thus A is responsible for his choice.

A, however, does not realize that he is inside of a time machine. The time machine rewinds the clock back until before t. This time at t, A chooses C2—which we know is logically possible.

We now have two equally valid outcomes. We have one timeline in which A chose C1, and one timeline in which A chose C2. Each timeline is equally valid morally-speaking, since in both timelines A is responsible for his choice.

From this, I see two implications. First, there seems to be no problem in saying that the man who controls the time machine can actualize whichever future he wants while still preserving the moral responsibility of A. Even if, on the second attempt, A chooses C1 again, as long as it is logically possible that A chooses C2 at t, the man in control can simply rewind again and again until A chooses C2. This would mean, of course, that for all free choices there are possible futures which are equally valid, and that whichever possible future becomes actual is an arbitrary matter (or dependent on the controller). "Arbitrary" here does not mean the choice itself is arbitrary; like I said, in both possible futures A is still responsible for his choice. But in some sense the actual world must be arbitrary. This, however, would be a monstrous threat to the kind of free will most religions wish to grant. Any omnipotent God has a power identical to that of the time machine (a power according to which that God might select the actual future from a set of possible futures). And since, according to this analysis of free will, both ends of a choice are possible futures, God can in theory actualize a world in which no free agent ever chooses evil, for example.

But, as a second implication, I would have to guess then that a free choice is not contingent in this indeterministic sense. There must be some defeater which says that A would contingently or would freely always choose C1 at t—giving the time machine no control of the actual future. Now, in order for A to remain morally responsible, we must still say that A could have done otherwise at t. But then, according to this analysis, we must also affirm that A would (never in a sense) have done other than A did at t. It seems to me, however, that saying A would never haven chosen C2 is equivalent to saying that A could never have willed to choose C2. But if A is restricted on what he can "will", then he seems to have no free will at all.

Two questions, then. Which is the correct understanding of free will: the one in which when we replay time the outcome of a free choice might be different (in which case a time machine can actualize whichever future it likes), or the one in which an agent would contingently always choose a particular end? And if the latter is correct, how does one make sense of "could have done otherwise" and moral responsibility with this kind of "would". I am having a hard time understanding this contingent kind of "would", which falls in between "might" (indeterminism, possibility) and "would" in the strong sense (determinism, necessity). Can someone help me construe this concept?

  • Free will isn't always taken to imply the sort of nondeterminism you talk about, sometimes it just means that free choices are a causal input that can't be reduced to other forms of causation like material interaction, see my comment here along with the linked pages. In particularly, in the philosophy of Molinism, God's omniscience is taken to imply counterfactual knowledge of what choice any agent would have made in a given set of external circumstances, implying that for each set of circumstances there would be a unique set of choices.
    – Hypnosifl
    May 12, 2020 at 20:26
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    "Could have done otherwise" is specific to libertarians, and to them it is truly indeterministic, there are no defeaters, compatibilists reject it as a condition for moral responsibility. Time machines are moot, "rewinding time" creates another timeline with another agent responsible for the choice there, whichever it might be. God can actualize worlds subverting free will, but won't due to omnibenevolence. "Would freely choose a predetermined outcome" is compatibilists' position, but "freely" only means lack of external coercion, accord with subject's wishes, which may well be predetermined.
    – Conifold
    May 13, 2020 at 2:26
  • @Hypnosifl Right, this is very connected to Molinist counterfactuals. I guess my issue is construing this idea of a what an agent "would freely" choose in a set of circumstances. What is this "would freely" based on? I can understand what it would be based on in a compatibilist picture; it would be based on the nature and desires of the agent in question. But I don't know how one would ground this idea on a libertarian view. You might just call it the "pure will" or something of an agent, but how do you characterize something like that?
    – natojato
    May 13, 2020 at 14:35
  • @Conifold Right, time machines would create different agents with different moral histories. But again, God choosing which future to actualize wouldn't subvert free will at all (if this indeterministic picture is right) since in all possible futures feature equally morally responsible agents, no?
    – natojato
    May 13, 2020 at 14:38
  • The picture with God actualizing timelines that fulfill counterfactuals of freedom is Molinist, and many religious libertarians reject it. According to them, God does not actualize timeline fully, free agents complete it by their choices, and even God does not know those fully because some of their aspects are not there to be known before the choice is made. "Based on nature and desires" only applies to limiting the choice, within those limits it is incoherent to ask what the choice is based on, it is free.
    – Conifold
    May 13, 2020 at 16:46


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