In my previous post, I looked at Cudworth’s argument that good and evil (and other moral features) cannot arise from decision alone, for something good cannot simply be made good by decision, without being also given the underlying nature of a good thing. Of course, his opponents have some possible responses open to them. Not all obligations, they might well argue, arise from the natures of the things we’re obliged to do. For instance, if I promise to do X, there may be nothing in X considered alone that makes it obligatory. But it nevertheless is obligatory, just because I promised to do it.
Cudworth does respond to that argument. He concedes something to the objection, but thinks that enough remains of his argument to show that Hobbes et al are mistaken.
For though it will be objected here, that when God, or civil powers command a thing to be done, that was not before obligatory or unlawful … the thing willed or commanded doth forthwith become obligatory … And therefore if all good and evil, just and unjust be not the creatures of mere will (as many assert) yet at least positive things must needs owe all their morality, their good and evil, to mere will without nature (TEIM 18).