Quasi-realism's problem of autonomous effects

Simon Blackburn defends a 'quasi-realist' view intended to preserve much of what realists want to say about moral discourse. According to error theory, moral discourse is committed to indefensible metaphysical assumptions. Quasi-realism seems to preserve ontological frugality, attributing no mistaken commitments to our moral practices. In order to make good this claim, quasi-realism must show that (a) the seemingly realist features of the 'surface grammar' of moral discourse can be made compatible with projectivism; and (b) certain realist-sounding statements which we might use in describing the nature of our moral commitments can be understood in projectivist terms. Much attention has been devoted to whether quasi-realism can deliver (a). I raise an important difficulty with regard to (b)