"How are moral assertions connected with the world of facts?"

Unlike many ancient philosophical problems, this one has, paradoxically, been made both more urgent and less tractable by the gradual triumph of scientific rationality. Indeed, the prevailing modern attitude towards it is a sort of dogmatic despair: ‘you can‘t get an ought from an is, therefore morality must be outside the domain of reason‘. Having fallen for that non-sequitur, one has only two options: either to embrace unreason, or to try living without ever making a moral judgement. In either case, one becomes a menace to oneself and everyone else.

On the tape of the bin Laden dinner party, a participant states his belief that during the September 11 attack, Americans were afraid that a coup d’état was under way. Worldwide, tens of millions of people believe that the Israeli secret service carried out the attack. These are factual misconceptions, yet they bear the imprint of moral wrongness just as clearly as a fossil bears the imprint of life. This illustrates an important strand in the fabric of reality: although factual and moral assertions are logically independent (one cannot deduce either from the other), factual and moral explanations are not. There is an explanatory link between ought and is, and this provides one of the ways in which reason can indeed address moral issues.

Jacob Bronowski pointed out that a commitment to discovering scientific truth entails a commitment to certain values, such as tolerance, integrity, and openness to ideas and to change. But there‘s more to it than that. Not only scientific discovery, but scientific understanding itself can depend on one’s moral stance. Just look at the difficulty that creationists have in understanding what the theory of evolution says. Look at the prevalence of conspiracy theories among the supporters of bad causes, and how such people are systematically blind to rational argument about the facts of the matter. And, conversely, look at Galileo, whose factual truth-seeking forced him to question the Church’s moral authority.

Why does this happen? We should not be surprised – at least, no more surprised than we are that, say, scientific and mathematical explanations are connected. The truth has structural unity as well as logical consistency, and I guess that no true explanation is entirely disconnected from any other. In particular, in order to understand the moral landscape in terms of a given set of values, one needs to understand some facts as being a certain way too, and vice versa. Moreover, I think it is a general principle that morally right values are connected in this way with true factual theories, and morally wrong values with false theories.

What sort of principle is this? Though it refers to morality, at root it is epistemological. It is about the structure of true explanations, and about the circumstances under which knowledge can or cannot grow. This, in turn, makes it ultimately a physical fact – but that is another story.

David Deutsch, a physicist, is a member of the Centre for Quantum Computation at the Clarendon Laboratory, Oxford University, and author of The Fabric of Reality.