Anyway, that’s interesting to hear that the meaning of “the dismal science” isn’t what I thought, or what most people thought, but rather something else entirely!

Actually, I wasn’t really committing myself to claims one way or another about whether or not economics is as successful as other sciences – I was just saying that it does in fact have the possibility of success, and presumably has achieved at least some minor degree of it.

But you’re probably right – Fish would think there is nothing real here, in economics or elsewhere. But he was careful in his post to limit his claims to “the arena of public debate”, so that’s where I wanted to point out just how drastic his claims are.

And I see that Mark Liberman of Language Log agrees.

This isn’t the origin of the phrase; it was coined by Thomas Carlyle, who objected to economics’ focus on material conditions:

““the Social Science … which finds the secret of this Universe in supply and demand and reduces the duty of human governors to that of letting men alone … is a dreary, desolate, and indeed quite abject and distressing one; what we might call … the dismal science.”

Apparently Carlyle was arguing for slavery and complaining that the economists’ view disrupted the natural relation between white and black people. Charming. (My respectable scholarly source.)

Anyway, I tend to agree with you that economics hasn’t been as successful at producing knowledge as the sciences it likes to model itself on, so that’s a nitpick.

Still, when you say this:
But if Fish is right, then there couldn’t even be such a thing as economic knowledge. There could be no evidence for or against trickle down economics – we just have to persuade people of its merits or demerits.
I suspect Fish would think that’s true of all fields of inquiry.