Brad DeLong is making a real monkey of himself

And I mean that as a compliment.

Specifically, he makes his way in the world using "a set of heuristic guesses made by a jumped-up monkey with a set of brain circuits designed to detect whether the fruit is ripe or it is safe to jump to the next branch".

And of course, that's true of all of us.

I do not know Nagel, so I will not jump into that particular fight with Gene Callahan. But speaking of monkey brains specifically, Gene trots out the tired old "if it's just a heuristic guess or convenient fiction then you can't prove the claim - you're just guessing about the fact that you're guessing!".

Right. That's the point.

And you're just guessing too. The thing is, Brad and I know we're guessing.

The metric is not whether we have plumbed the depths of objective reality. That sounds like a good metric on paper, but it's not a metric that we have access to. Instead of criticizing Brad on the basis of a metric that neither Gene nor Brad have available to them, perhaps we should come up with a different metric. Something like "does this heuristic seem to help me navigate the world".

That doesn't pose the same sort of problems as the metric of consistency with objective truth. We may argue about it, but I don't see what's wrong with that. Gene and I may never agree about the claims that best help us navigate the world, but I Gene and I can both have more confidence in the sentence "this claim helps me navigate the world" than the sentence "this claim is consistent with objective truth".

That seems pretty good to me.

And it turns out that even though we have to accept a degree of pluralism and disagreement when we abandon "objective truth", we still seem to generate a fair amount of agreement. It's not hopelessly disordered. There seems to be enough consistency in peoples' subjective experience that we can generate a set of claims that a lot of people agree with.

What more could you ask for? That's pretty good for a monkey, right?

UPDATE: Nagel's way of thinking, of course, is itself a heuristic that does a decent job helping people navigate their world. It staves off existential anxieties, explains the order we see, reinforces social institutions, along with all sorts of other benefits. That's why it endures. That's even why it's worth talking that way sometimes. But that doesn't mean it is "true" in the "objective truth" sense of the word "true".