If you want a more concrete example of what Parfit took to be an irreducibly normative truth, it might be that the fact that if I do X, someone will be in agony is a reason against doing X (not necessarily a conclusive reason, of course).
When Parfit said that if there are no such truths, nothing would matter, he meant that nothing would matter in an objective sense. It might matter to me, of course. But it wouldn’t really matter. I agree with that, although I can also see that the fact that something matters to me, or to those I love and care about, does give me a reason not to do it. For more discussion, see the collection of essays I edited, Does Anything Really Matter (Oxford, 2017). The intention, when I conceived this volume, was for Parfit to reply to his critics in the same volume, but his reply grew so long that it had to be published separately, and it forms the bulk of On What Matters, Volume Three.
If you want a more concrete example of what Parfit took to be an irreducibly normative truth, it might be that the fact that if I do X, someone will be in agony is a reason against doing X (not necessarily a conclusive reason, of course).
When Parfit said that if there are no such truths, nothing would matter, he meant that nothing would matter in an objective sense. It might matter to me, of course. But it wouldn’t really matter. I agree with that, although I can also see that the fact that something matters to me, or to those I love and care about, does give me a reason not to do it. For more discussion, see the collection of essays I edited, Does Anything Really Matter (Oxford, 2017). The intention, when I conceived this volume, was for Parfit to reply to his critics in the same volume, but his reply grew so long that it had to be published separately, and it forms the bulk of On What Matters, Volume Three.