The appealing principle that you can't get an ‘ought’ from an ‘is’, sometimes called Hume's Guillotine , faces a well-known challenge: it must give a clear account of the distinction between normative and descriptive sentences while dodging counter-examples. I argue in this paper that recent efforts to answer this challenge fail because the distinction between normative and descriptive sentences cannot be described well enough to be of any help. As a result, no version of the principle is both true and (...) adequate. Yet a different principle—that no normative terms are synonymous with any descriptive terms—can satisfy much of the motivation we had for defending Hume's Guillotine in the first place. I show briefly how this second principle can explain why is-ought arguments are invalid, block some attempted deductive justifications of beliefs with normative terms, and create an explanatory advantage for moral non-cognitivism. Just so, giving up Hume's Guillotine is the prudent thi.. (shrink)

I defend the following version of the ought-implies-can principle: (OIC) by virtue of conceptual necessity, an agent at a given time has an (objective, pro tanto) obligation to do only what the agent at that time has the ability and opportunity to do. In short, obligations correspond to ability plus opportunity. My argument has three premises: (1) obligations correspond to reasons for action; (2) reasons for action correspond to potential actions; (3) potential actions correspond to ability plus opportunity. In the (...) bulk of the paper I address six objections to OIC: three objections based on putative counterexamples, and three objections based on arguments to the effect that OIC conflicts with the is/ought thesis, the possibility of hard determinism, and the denial of the Principle of Alternate Possibilities. (shrink)

My first paper on the Is/Ought issue. The young Arthur Prior endorsed the Autonomy of Ethics, in the form of Hume’s No-Ought-From-Is (NOFI) but the later Prior developed a seemingly devastating counter-argument. I defend Prior's earlier logical thesis (albeit in a modified form) against his later self. However it is important to distinguish between three versions of the Autonomy of Ethics: Ontological, Semantic and Ontological. Ontological Autonomy is the thesis that moral judgments, to be true, must answer to a realm (...) of sui generis non-natural PROPERTIES. Semantic autonomy insists on a realm of sui generis non-natural PREDICATES which do not mean the same as any natural counterparts. Logical Autonomy maintains that moral conclusions cannot be derived from non-moral premises.-moral premises with the aid of logic alone. Logical Autonomy does not entail Semantic Autonomy and Semantic Autonomy does not entail Ontological Autonomy. But, given some plausible assumptions Ontological Autonomy entails Semantic Autonomy and given the conservativeness of logic – the idea that in a valid argument you don’t get out what you haven’t put in – Semantic Autonomy entails Logical Autonomy. So if Logical Autonomy is false – as Prior appears to prove – then Semantic and Ontological Autonomy would appear to be false too! I develop a version of Logical Autonomy (or NOFI) and vindicate it against Prior’s counterexamples, which are also counterexamples to the conservativeness of logic as traditionally conceived. The key concept here is an idea derived in part from Quine - that of INFERENCE-RELATIVE VACUITY. I prove that you cannot derive conclusions in which the moral terms appear non-vacuously from premises from which they are absent. But this is because you cannot derive conclusions in which ANY (non-logical) terms appear non-vacuously from premises from which they are absent Thus NOFI or Logical Autonomy comes out as an instance of the conservativeness of logic. This means that the reverse entailment that I have suggested turns out to be a mistake. The falsehood of Logical Autonomy would not entail either the falsehood Semantic Autonomy or the falsehood of Ontological Autonomy, since Semantic Autonomy only entails Logical Autonomy with the aid of the conservativeness of logic of which Logical Autonomy is simply an instance. Thus NOFI or Logical Autonomy is vindicated, but it turns out to be a less world-shattering thesis than some have supposed. It provides no support for either non-cognitivism or non-naturalism. (shrink)

In a dense and fascinating article of some ten years ago, Toomas Karmo adds his voice to the chorus of philosophers who deny the possibility of soundly deriving ‘ought’ from ‘is.’ According to Karmo, no derivation containing an ethical conclusion and only non-ethical premises can possibly be sound, where ‘sound’ describes a deductively valid derivation all of whose premises are true. He also suggests that the only valid derivations of ‘ought’ from ‘is’ will be trivial ones. His argument has, to (...) my knowledge, gone unrebutted; on the contrary, it has won recent endorsements, some philosophers evidently believing that he has finally put to rest the issue of the logical autonomy of ethics. Against that trend, I intend to rebut his argument, both by falsifying the taxonomy on which his argument relies and by offering a nontrivial and potentially sound ‘is’-‘ought’ derivation of my own. (shrink)

In a dense and fascinating article of some ten years ago, Toomas Karmo adds his voice to the chorus of philosophers who deny the possibility of soundly deriving ‘ought’ from ‘is.’ According to Karmo, no derivation containing an ethical conclusion and only non-ethical premises can possibly be sound, where ‘sound’ describes a deductively valid derivation all of whose premises are true. He also suggests that the only valid derivations of ‘ought’ from ‘is’ will be trivial ones. His argument has, to (...) my knowledge, gone unrebutted; on the contrary, it has won recent endorsements, some philosophers evidently believing that he has finally put to rest the issue of the logical autonomy of ethics. Against that trend, I intend to rebut his argument, both by falsifying the taxonomy on which his argument relies and by offering a nontrivial and potentially sound ‘is’-‘ought’ derivation of my own. (shrink)

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)

Various formally valid counterexamples have been adduced against the Humean dictum that one cannot derive an “ought” from an “is.” There are formal rebuttals—some very sophisticated now (e.g., Charles R. Pigden’s and Gerhard Schurz’s)—to such counterexamples. But what follows is an intuitive and informal argument against them. I maintain that it is better than these sophisticated formal defenses of the Humean dictum and that it also helps us see why it implausible to think that we can be as decisive about (...) the truth or falsity of the dictum as both the formal counterexamples or formal barriers to them purport to be. (shrink)