Three fixity principles

In debates about free will and foreknowledge as well as about compatibility and incompatibilism, fixity-of-history theses come up. Here is such a thesis:

1. If a decision is causally or logically necessitated by the history behind the decision, then one could not have decided otherwise.

But now we have a crucial question as to what is meant by “the history behind the decision”. There are at least two takes on this. On the temporal version, the history behind the decision is the sum total of what happened temporally prior to the decision. On the causal version, the history is the sum total of what happend causally prior to the decision.

This is not just a nitpicking question. Linda Zagzebski for instance nicely shows that if we go for the causal-history version of (1), then the main argument for the incompatibility of free will and foreknowledge does not get off the ground assuming God’s forebelief is not causally prior to the action. On the other hand, if we go the temporal-history version, then we have a prima facie argument for such incompatibility (though I think it’s blockable).

I am pretty confident that we should go for the causal-history version, and this has to do with the fact that the temporal-history version is not strong enough to capture our fixity intuitions. Suppose that we live in a world with simultaneous causation—say, a Newtonian world with rigid objects such that if you push object A and A pushes B, then B begins to move at exactly the same time as you start pushing (rather than with a delay caused by then need for a compression wave traveling through nonrigid materials at less than the speed of light). Then we could imagine cases where someone’s decision is causally necessitated by something outside the agent that is simultaneous with the decision. Such causal necessitation would just much make it true that one could not have decided otherwise as would causal necessitation by something in the past.

Furthermore, if backwards causation is possible, then a neurosurgeon in the future who used a backwards-causing machine to determine your decision would clearly prevent you from deciding otherwise, even though the neurosurgeon’s action was not in the temporal history. We may not believe backwards causation is possible, but it is clear that if it were possible, then deterministic backwards causation would be just as threatening for free decisions as deterministic forwards causation. This shows that causal determination is indeed a threat.

Of course, my above argument only shows that if we need to choose between the causal and temporal history versions of (1), we should definitely go for the causal one. But perhaps we don’t need to choose. We could accept both versions. But if we think we accept both versions, I think what we really should accept is an even stronger principle, where “history” is causal-cum-temporal (cct). On that stronger principle, event A counts as in the cct history of event E provided that it is either temporally or causally prior to E. The resulting fixity principle is pretty strong principle, but also a bit gerrymandered. And I think accepting this principle not that plausible, because the much simpler causal version captures our intuitions about all the ordinary cases (not involving God, or backwards or simultaneous causation), since in all ordinary cases causal and temporal history coincide, and we should not go for a more complex principle without pretty good reason.

Frankfurt and functionalism

We learn from Frankfurt counterexamples to the Principle of Alternate Possibility that we should not use counterfactuals and nomic modality to characterize intrinsic features of things. What Frankfurt cases show is that it is frequently possible to modify counterfactual and nomic modal properties of a thing, event or process without actually causally affecting the thing, event or process in itself.

This is a useful lesson. Here is one interesting application: standard functionalist theories of mind cannot be right. I will give the roughest sketch of the argument. Start with two observations:

1. Functional characterizations of a system depend crucially on the system's counterfactual properties. (An and-gate is a system of which it is true that it would produce a 0 given two 0's or one 0 and one 1, and would produce a 1 given two 1's, even if in the course of the system's functioning it is actually only fed one of these options.)
2. That a system exemplifies a functioning mind is an intrinsic property of the system.

Now, what we learn from Frankfurt cases is that we can radically alter the counterfactual properties of a system in just about any way we wish without actually causally interacting with the system, and hence without altering its intrinsic properties. It follows from this observation and (1) and (2) that whether a system exemplifies a functioning mind cannot be a matter of the system's functional characterization. (We can, for instance, make sure that a given logic gate could never have produced a different output from what it actually produced, because someone watching the system would have intervened and forced it to produce the output it actually produced, had this watcher seen the inputs being different. But if this were done, then this would not be an and-gate, as it would not have the counterfactual properties of the relevant kind of logic gate.)

I should say that there is a way out of this argument, and it is to embrace an Aristotelian functionalism that instead of characterizing functions counterfactually, characterizes them teleologically. But that is not what "functionalism" means in the context of the theory of mind. (One might also try to do the Aristotelian move and define the functionalism evolutionarily. But not hard to see that this fails [e.g., see this, or this, or just extend the argument here].)

Or maybe we could try to get out of the argument by supposing that we can cut a system away from its environmental context and characterize the functioning of the system by looking at how the system would function apart from its environment, thereby isolating the system from the kind of purely counterfactual interference that a Frankfurt-style watcher would impose on it. But that simply doesn't work. How does the human body work absent its environmental context? It simply dies, pretty quickly, when not supplied with air, food and water.

Of course one might try to define a notion of an appropriate environment and then calculate the counterfactuals relative to that. But if we are allowed to be completely free in choosing what environment counts as appropriate, then just about everything is up for grabs. And if there is an objectively appropriate environment for the system, then again we get some version of Aristotelian teleology, which is not what functionalism wants.