“In every system of morality, which I have hitherto met with, I have remarked, that the author proceeds for some time in the ordinary way of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when of a sudden I am surprized to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not …
… This change is imperceptible; but is, however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, ’tis necessary that it should be observed and explained; and at the same time that a reason should be given, for what seemed altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it.”
In this celebrated passage from his Treatise of Human Nature, the Scottish philosopher David Hume gives, in his usual laconic manner, the classic formulation of what has since remained one of the central questions in moral philosophy. How can we possibly move from a descriptive statement about how things stand in the world (an “is” statement) to a prescriptive statement telling us what ought to be done (an “ought” statement)? Or put briefly, how can we derive an “ought” from an “is”? Hume evidently thinks that we cannot and many thinkers have agreed with him, believing that “Hume’s guillotine” (or more prosaically, “Hume’s law”) has decisively severed the world of fact from the world of value.
“Perhaps the simplest and most important point about ethics is purely logical. I mean the impossibility to derive non-tautological ethical rules … from statements of facts.”
Karl Popper, 1948
The naturalistic fallacy Hume’s law is often confused with a related but distinct view put forward by the English philosopher G.E. Moore in his Principia Ethica (1903). Moore accused earlier philosophers of committing what he called the “naturalistic fallacy,” which involves identifying ethical concepts with natural concepts; thus “good,” for instance, is taken to mean the same thing as (say) “pleasurable.” But, Moore alleged, it is still an open question to ask whether what is pleasurable is also good—the question is not vacuous—so the identification must be mistaken.
Moore’s own view (which has been much less influential than the supposed fallacy that he identified) was that ethical terms such as “good” are “nonnatural” properties—simple and unanalyzable properties, accessible only by means of a special moral sense known as “intuition.”
To confuse matters further, the expression “naturalistic fallacy” is sometimes used for the completely different mistake—much beloved of advertisers—of claiming that the fact that something is natural (or unnatural) provides sufficient grounds for supposing that it is also good (or bad). Victims of natural pathogens undergoing treatment with synthetic drugs would readily testify to the flawed nature of this argument.
Value in a value-free world The problem that Hume has highlighted is due in part to two strong but conflicting convictions that many of us share. On the one hand, we believe that we live in a physical world that can in principle be fully explained by laws discoverable by science; a world of objective fact from which value is excluded. On the other hand, we feel that in making moral judgments, for instance that genocide is wrong, we are stating something true about the world; something that we can know and which would be true anyway, irrespective of how we might feel about it. But these views appear to be incompatible if we accept Hume’s law; and if we cannot ground our moral evaluations in the value-free world described by science, we are apparently forced back upon our own feelings and preferences and must look within ourselves to find the origins of our moral sentiments. Hume himself was not unaware of the significance of his observation, believing that if proper heed were given to it “all the vulgar systems of morality” would be subverted. The logically unbridgeable gap between fact and value that Hume seems to open up casts doubt over the very status of ethical claims and thus lies at the heart of moral philosophy.
Ethics, or moral philosophy, is often divided into three broad areas. At the most general level, metaethics investigates the source or basis of morality, including such questions as whether it is essentially objective or subjective in nature. Normative ethics focuses on the ethical standards (or norms) on which moral conduct is based; thus utilitarianism, for instance, is a normative system based on the standard of “utility.” Finally, at the lowest level, applied ethics brings philosophical theory to bear on practical issues, such as abortion, euthanasia, just war and the treatment of animals. Philosophers have taken an array of positions on all these questions; and with these come many -isms. The following gives a thumbnail sketch of some of the most commonly encountered of these ethical positions.
the condensed idea
The is-ought gap
| Timeline | |
|---|---|
| c.440BC | One man’s meat … |
| AD1739 | Hume’s guillotine The boo/hoorah theory |
| 1781 | The categorical imperative |
| 1785 | Ends and means |