This paper proves a precisification of Hume’s Law—the thesis that one cannot get an ought from an is—as an instance of a more general theorem which establishes several other philosophically interesting, though less controversial, barriers to logical consequence.

Are there good arguments from Is to Ought? Toomas Karmo has claimed that there are trivially valid arguments from Is to Ought, but no sound ones. I call into question some key elements of Karmo’s argument for the “logical autonomy of ethics”, and show that attempts to use it as part of an overall case for moral skepticism would be self-defeating.

In the current issue of this journal, Scott Hill critiques some of my work on the “is”-“ought” controversy, the Hume-inspired debate over whether an ethical conclusion can be soundly, or even validly, derived from only non-ethical premises. I’ve argued that it can be; Hill is unconvinced. I reply to Hill’s critique, focusing on four key questions to which he and I give different answers.

Hume seems to claim that there does not exist a valid argument that has all non-ethical sentences as premises and an ethical sentence as its conclusion. Starting with Prior, a number of counterexamples to this claim have been proposed. Unfortunately, all of these proposals are controversial. Even the most plausible have a premise that seems like it might be an ethical sentence or a conclusion that seems like it might be non-ethical. Since it is difficult to tell whether any of (...) these counterexamples are genuine, we need a taxonomy that sorts out ethical sentences from non-ethical ones. We need to know the difference between an ‘Is’ and an ‘Ought’. In the first part of the paper, I establish the need for a taxonomy. I consider some of the most influential ‘Is’–‘Ought’ derivations. These include proposals by Prior and Searle. I argue that each proposal has a premise whose status as ethical or non-ethical is difficult to determine. In the second part of the paper, I consider taxonomies proposed by Karmo and Maitzen. I argue against both taxonomies. I end with the claim that we need a taxonomy of ethical sentences and that none of the current proposals are adequate. (shrink)

Toomas Karmo claims that his taxonomy of ethical sentences has the result that there does not exist a sound argument with all non-ethical premises and an ethical conclusion. In a recent paper, Mark T. Nelson argues against this claim. Nelson presents a sound argument that he takes to be such that (i) Karmo’s taxonomy classifies that argument’s single premise as non-ethical and (ii) Karmo’s taxonomy classifies that argument’s conclusion as ethical. I attempt to show that Nelson is mistaken about (ii). (...) For any possible world at which the premise of Nelson’s argument is true, Karmo’s taxonomy classifies the conclusion of Nelson’s argument as non-ethical. (shrink)