Having previously agreed there is no issue with deontically necessitating constraints analogous to the modal ones for material incompatibility and material consequence, I’m now starting to wonder if this might be as far as Brandom’s deontology really goes anyway.
When I hear “deontology”, I hear rigid rules for everything going all the way to the practical last instance, and feel compelled to defend the place of an always somewhat open Aristotelian practical judgment (phronesis) in contrast to it. But I would rather not attribute such rigidity to Brandom or Kant, both of whom emphasize kinds of rules that are actually higher-order. A simultaneously logical and ethical necessitation of respect for abstract principles like material incompatibility and material consequence can be fully granted without reducing what we should do in concrete situations to a deterministic formula. I want to say that first-order rules belong in logic and mathematics, not ethics.
It feels a bit ironic that I am the one effectively appealing for a need for freedom here, but it really shouldn’t. It’s freedom of reason, not any appeal to will. (See also Evaluation of Actions; Necessity in Normativity; Binding; Robust Recognition; Mutual Recognition; Euthyphro.)