Hmm, that seems like a fairly banal observation. Of course you can't tell whether someone has free will looking from the outside. In the general case the behavior of someone with free will will be indistinguishable from random behavior. If free will was just about patterns of behavior then it wouldn't be a very interesting philosophical issue.

Here's the paper he wrote on it, I think it'd be good to take a look at it directly.

https://arxiv.org/abs/1306.0159

Scott is making a pair of claims: If it's possible to build a fast, noninvasive, perfect predictor then what more can science say to show that people don't have free will?

If it's impossible to build such a predictor, for some fundamental reason, then what more can science say to show that free will exists.

Ah, in the paper he says that he's not actually talking about free will. That makes it less confusing. But I still think he's making much too strong a connection between Knightian unpredictability and free will. I don't see any reason at all to think that the former is a necessary condition for the latter, and he doesn't really attempt to argue the point. (He promises that he's going to argue it in section 2.5, but then section 2.5 ends up only talking about problems of personal identity.)

>Of course you can't tell whether someone has free will looking from the outside.

Before quantum mechanics and uncomputability, the "of course" went the other direction.

I don't see how that makes any difference. Could you expand?

I don't think it's obvious that you can't tell whether someone has free will from the outside. Considering the enormous success physics has had with explaining every other phenomenon from the outside, that seems like a very strong statement.

How would you distinguish decisions that were freely made from decisions made at random?

If we can't, then that says something doesn't it?

I just don't see how. It seems like a fairly obvious point that the two systems would be indistinguishable from the outside.

In that case, the pragmatists would say that the distinction isn't meaningful, that free will is a concept with no meaning, and end the debate there.

I don't think it's plausible to maintain that the question of whether or not we have free will is "meaningless". Any criterion of meaningfulness that derives that conclusion is probably faulty.