I’ve written all this before, but let me try to summarize the argument more succinctly.
The Consequence Argument reduces succinctly to:
The laws of nature, in conjunction with antecedent events, necessitate all future events, including all human acts.
The crux of the dispute, as I see it, lies in two words from above: “laws” and “necessitate.”
The Humean compatibilist, of which I, roughly, am one, denies that the “laws” of nature are laws at all. The so-called laws are descriptions of what happens in the world. They are not, and cannot be, prescriptions. Those who think otherwise have the burden or proof to show that laws are actually prescriptive.
If laws are merely descriptive rather than prescriptive, then the first prop of the Consequence Argument is knocked out from under it. If laws are descriptions, as I hold, then at least some “laws” of nature are up to us.
Now move on to the word “necessitate.” As I have repeatedly pointed out, the use of the word “necessitate” in this context commits the modal fallacy.
As I have also pointed out, there are other forms of determinism besides causal determinism. All these forms of determinism, when they argue against free will, commit the modal fallacy.
Logical determinism is the thesis that if there are true propositions about future contingents events, then these propositions are not actually contingent (could be otherwise). So, if today it’s true that tomorrow I will do x, then tomorrow I must do x. No free will.
The fallacy here, as I’ve pointed out, lies in the misallocation of the modal necessity operator. In the above, it must be applied jointly to both the antecedent and its consequent, and not just to the consequent. Hence the corrected argument is:
Necessarily (if today it is true that tomorrow I will do x, then tomorrow I will (not must) do x. Free will restored.
Epistemic determinism is the thesis that if an omniscient observer knows in advance that I will do x, then I must do x. No free will.
Again, this is an example of the modal fallacy, and the repaired argument goes:
Necessarily (if an omniscient observer knows in advance that I will do x, then I will (not must) do x. Free will restored.
Causal determinism is the thesis that given antecedents a, b, and c, then later I must do x.
Modally repaired:
Necessarily (if antecedents a, b, and c, then later I will (not must) do x. Free will restored.
As an example, suppose this morning I had a big breakfast because last night I skipped dinner. It does not follow that I had to have a big breakfast, I just did because antecedently I had refrained from eating.
The standard compatibilist agrees with the hard determinist that given antecedents a, b, and c, x follows. They part company on this point: the hard determinist maintains that x
must follow, whereas the standard compatibilist holds nothing more than that x
will follow.
The Humean compatiblist, as also previously noted, thinks that, because “laws” are descriptive and not prescriptive, x does not follow from a, b, and c. Rerunning the tape of history with antecedents exactly the same will yield different results (though this is not an experiment we can run, of course.) For a full treatment of this issue see chapters 10 and 11 of the book The Concept of Physical Law by Norman Swartz. The whole book can be downloaded for free
here.
For a different take on the subject, I recommend David K. Lewis’s classic paper,
“Are We Free to Break the Laws?” It is a rebuttal of van Inwagen’s Consequence Argument but taking a different line.