It’s not unheard of to encounter claims to the effect that there’s something irreducibly normative about things epistimic and/or mental, that failure of derivability of “ought”’s from “is”’s somehow is significant for philosophy of mind.
I’ve always found this to be a bit of a head-scratcher, though, and have had recent occasion to contemplate it again in commenting on Ignacio Prado’s Transcendental Argument Against Physicalism. The following is adapted from my comment on that post:
There are two main problems that arise for the claim that “statements about what we have reason to believe have the logical form of ought-statements, and ought-statements cannot be derived from is-statements”:
1. That you can’t derive “ought”’s from “is”’s isn’t exactly clear or noncontroversial. 2. That evidence for belief is relevantly normative isn’t exactly clear or noncontroversial.
Re 1. It’s not just any statement with an ‘ought’ in it that resists derivation from a statement without an ‘ought’. Consider,for example, hypothetical imperatives like “If you want to catch a fish, you ought to put a worm on your hook.” That may very well just be expressing a counterfactual conditional. For the allegedly nonreducibly normative, you need (a) genuinely categorical imperatives that (b) are truth evaluable. “You ought to put a fish on your hook” is a categorical imperative only on the face of it, for in certain contexts it will be clear that it is really just expressing the aforementioned hypothetical imperative. “You ought to pay your debt to me” might arguably be a genuine categorical imperative, but it remains open to be argued that it is not truth evaluable. It may instead simply function as a command (”pay me your debt”) or a long-winded hooray (”yay for those who pay their debts to me”).
Re: 2. So, what are the genuine truth evaluable categorical epistemic imperatives? Is an example “You ought to believe what the evidence supports”? If so, what makes you so sure it satisfies the criteria set forth in the remarks above?