As I understand the B-theory of time it says that we can talk about things happening in time just by using tenseless sentences — which for me implies that the past, present and future are equally real.

Is the B-theory of time incompatible with libertarian free will? It does seem so for me: if the future is as real as the past, it is as determined as the past. I can't do otherwise (in the libertarian sense of "can") as I do now.

Am I right, or is there a way to make the B-theory compatible with libertarianism?


First, B theory is a semantic theory about the proper way to refer to events in time, not a metaphysical theory about past and future events. The view that past and future events are real is called eternalism. It's true that B theory fits better with eternalism than with other metaphysical theories of time, but strictly speaking they are distinct.

Second, eternalism and determinism are also distinct views. Determinism is the view that the future is determined by the past and by the laws of nature, but it is conceivable that future facts are real although they are not determined by laws (for example: the exact same state A evolves into either B or C at different places or times so determinism is false).

Regarding compatibility with libertarian free will, the crucial aspect is necessity. Libertarian free will is sometimes expressed as follows: an agent could have done otherwise, which, roughly, means that what the agent did was not necessary.

Libertarian free will is incompatible with determinism because if everything happens in virtue of the laws of nature, and if the laws of nature express relations of necessity in the world, then it is not true that an agent could have done otherwise.

However libertarian free will is not strictly incompatible with eternalism. Saying that future events are real does not mean that they will happen in virtue of necessity so there is room for a combination of libertarian free will and eternalism.

Having said that, this is quite a formal reasoning and our intuitions speak differently. Most defenders of libertarian free will would probably say that it requires that the future is open, i.e. that future events are not (yet) settled for us to have any choice. This intuition can be cast in terms of necessity: one could argue that something that is the case is necessarily the case, so that if every fact is settled in eternity, then everything true (including about future facts) is also necessary, and that therefore eternalism is incompatible with libertarian free will.


I think you're conflating a few things that are often conflated to reach your conclusion. I'll do my best to sort out what I think needs to happen:

  1. B-theory = past, present, future are identically facts with knowable truth-values.
  2. Libertarian freedom means that an agent can make "free choices" where free means not subject to any prior determination
  3. Prior knowability = prior determination
  4. Ergo, 1 and 2 are incompatible.

But claim 3 is not trivially true. And that's the challenge here. It seems to follow sometimes but not always. The root question is whether that something will be the case is the cause that something will be the case or merely the observation that something will be the case.

There's a very large debate about the nature of necessity and the meaning of necessity that also gets involved here. If there's only one form of necessity than 3 seems to follow. If there's multiple forms of necessity, then it is conceivable that something is necessary but non-causitive insofar as the necessity is metaphysically contingent on something and granting that there's a distinction between logical sequence and temporal sequence. You need the second because merely because something is temporally necessitated (through the stative nature of the future) does not mean that it's origination is logically necessitated (in the manner in which prior present and future events relate).

  • Also with libertarian free will it's usually meant that decisions are "up to us", if the future is determined, how can that be?
    – R. Neville
    Dec 6 '15 at 0:29
  • Sorry, I'm not really grasping either of your comments per se. I would take it that you are wanting to work through a philsoophical definition of determinism -- not wikipedia. And I'm expressing your second comment by 3 in my argument. There's no immediate and evident contradiction between the future being factual (B-theory) and us being unable to make choices. It only happens when you add the assumption that what is known is determined, which doesn't necessarily follow.
    – virmaior
    Dec 6 '15 at 0:32
  • Would you agree to: "If future events can be known as a fact, they are unavoidable." ?
    – R. Neville
    Dec 6 '15 at 0:38
  • There's an equivocation going on there. What does "unavoidable" mean in that sentence? If "unavoidable" just means 'it will happen', then it doesn't follow. If "unavoidable" means 'completely already set in motion by prior events', then it does follow. In other words, you're accepting 3. Simply put, you need to accept 3 in order for the B-theory to equate to determinism. If you do, then you think B-theory and libertarian free will are incompatible. If not, then it's possible for them to be compatible.
    – virmaior
    Dec 6 '15 at 1:29
  • (ps in general, "am I right questions?" are actually off-topic for this SE... the basic reason being SE is not designed for debates. If you're wondering about whether B-theory automatically implies no libertarian freedom then I would say my answer addresses that. )
    – virmaior
    Dec 6 '15 at 1:32

you are right. the definition of libertarian/incompatibilist-free-will is exactly: could you have done otherwise of your own volition. The definition is like a hypothetical question about the past. When this type of definition is defined as 'incompatible with determinism', it's doesn't matter whether our world really is deterministic, its only to understand what the person using the term means. The 'of your own volition' is added since we don't know for a fact whether our world is deterministic, so as to include indeterminism (some particle moving via-probability ("randomly") in my brain could hypothetically change what i had done in the past, but that random movement isn't my volition). Its added basically just to specify that we're asking: could you have done otherwise under the exact exact same circumstances.

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