Charles R. Pigden

I argue 1) That in his celebrated Is/Ought passage, Hume employs ‘deduction’ in the strict sense, according to which if a conclusion B is justly or evidently deduced from a set of premises A, A cannot be true and B false, or B false and the premises A true. 2) That Hume was following the common custom of his times which sometimes employed ‘deduction’ in a strict sense to denote inferences in which, in the words of Dr Watts’ Logick, ‘the premises, according to the reason of things, do really contain the conclusion that is deduced from them’; that although Hume sometimes uses ‘demonstrative argument’ as a synonym for ‘deduction’, like most of his contemporaries, he generally reserves the word ‘demonstration’ for deductive inferences in which the premises are both necessary and self-evident. 3) That Mr Hume did indeed mean to suggest that deductions from IS to OUGHT were ‘altogether inconceivable’ since if ought represents a new relation or affirmation, it cannot, in the strict sense, be justly deduced from premises which do not really contain it. 4) That in a large and liberal (or perhaps loose and promiscuous) sense Hume does deduce oughts and ought nots from observations concerning human affairs, but that the deductions in question are not inferences, but explanations, since in another sense of ‘deduce’, common in the Eighteenth Century, to deduce B from A is to trace B back to A or to explain B in terms of A; 5) That a small attention to the context of Hume’s remarks and to the logical notions on which they are based would subvert those vulgar systems of philosophy which exaggerate the distinction between fact and value; for just because it is ‘altogether inconceivable’ that the new relation or affirmation OUGHT should be a deduction from others that are entirely different from it, it does not follow that the facts represented by IS and IS NOT are at bottom any different from the values represented by OUGHT and OUGHT NOT.

It ‘seems altogether inconceivable', says Hume, that this ‘new relation' ought ‘can be a deduction' from others ‘which are entirely different from it' The idea that you can't derive an Ought from an Is, moral conclusions from non-moral premises, has proved enormously influential. But what did Hume mean by this famous dictum? Was he correct? How does it fit in with the rest of his philosophy? And what does this suggest about the nature of moral judgements? This collection, the first on this topic for forty years, assembles a distinguished cast of international scholars to discuss these questions. The book combines, historical scholarship, meta-ethics and cutting-edge research in philosophical logic. It includes three distinct attempts to reformulate and prove No-Ought-From-Is in the face of Prior's famous counterexamples. Contributors: A.N. Prior, Gerhard Schurz, Charles Pigden, J.M.Shorter, Annette.C.Baier, Wade Robison, Adrian Heathcote, Alan Musgrave, Norva Y.S. Lo, Gillian Russell, Hakan Salwén, Greg Restall, Peter Vranas, Edwin Mares, Stephen Maitzen

According to the truthmaker theory that we favour, all contingent truths are made true by existing facts or states of affairs. But if that is so, then it appears that we must accept the existence of the negative facts that are required to make negative truths (such as 'There is no hippopotamus in the room.') true. We deny the existence of negative facts, show how negative truths are made true by positive facts, point out where the (reluctant) advocates of negative facts (Russell, Armstrong, et al.) went wrong, and demonstrate the superiority of our solution to the alternatives.

In his metaphysical summa of 1986, The Plurality of Worlds, David Lewis famously defends a doctrine he calls ‘modal realism’, the idea that to account for the fact that some things are possible and some things are necessary we must postulate an infinity possible worlds, concrete entities like our own universe, but cut off from us in space and time. Possible worlds are required to account for the facts of modality without assuming that modality is primitive – that there are irreducibly modal facts. We argue that on one reading, Lewis’s theory licenses us to assume maverick possible worlds which spread through logical space gobbling up all the rest. Because they exclude alternatives, these worlds result in contradictions, since different spread worlds are incompatible with one another. Plainly Lewis’s theory must be amended to exclude these excluders. But, we maintain, this cannot be done without bringing in modal primitives. And once we admit modal primitives, bang goes the rationale for Lewis’s modal realism.

Conpiracy theories are widely deemed to be superstitious. Yet history appears to be littered with conspiracies successful and otherwise. (For this reason, "cock-up" theories cannot in general replace conspiracy theories, since in many cases the cock-ups are simply failed conspiracies.) Why then is it silly to suppose that historical events are sometimes due to conspiracy? The only argument available to this author is drawn from the work of the late Sir Karl Popper, who criticizes what he calls "the conspiracy theory of society" in The Open Society and elsewhere. His critique of the conspiracy theory is indeed sound, but it is a theory no sane person maintains. Moreover, its falsehood is compatible with the prevalence of conspiracies. Nor do his arguments create any presumption against conspiracy theories of this or that. Thus the belief that it is superstitious to posit conspiracies is itself a superstition. The article concludes with some speculations as to why this superstition is so widely believed.