Sources & Extracts

Review this excerpt and then go back to the main thread.

The philosophical problem described as "deriving ought from is" is at least as old as the writings of the Scottish philosopher David Hume. In Book III of A Treatise of Human Nature Hume provided one of the most widely quoted paragraphs in the history of western philosophy:

In every system of morality, which I have hitherto met with, I have always remark'd, 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 surpriz'd 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 shou'd be observ'd and explain'd; and at the same time that a reason should be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it. But as authors do not commonly use this precaution, I shall presume to recommend it to the readers; and am persuaded, that this small attention wou'd subvert all the vulgar systems of morality....

From David Hume, A Treatise of Human Nature, Book III, p. 469, Selby-Bigge edition, 1967. Hume first published Book III in 1740.

A more recent discussion can be found in Brandt's Ethical Theory. Brandt describes the situation as follows:

First of all, one cannot formally deduce an ethical statement from a set of premises that does not contain any ethical statements. To understand this, let us look at a sample of deductive reasoning that is valid -- a simple example of syllogistic reasoning, which for our purposes can be taken as representative of deductive reasoning in general.

PREMISE 1:Any act that maximizes happiness for all affected, among those open to an agent, is right.
PREMISE 2: Under circumstances Z (specified), telling a (specified) lie to Mr. A will maximize happiness for all concerned.
CONCLUSION: Therefore, telling a lie (as specified) to Mr. A under circumstances Z is right.

The point to notice about this example of valid reasoning is that the term "right" could not have appeared validly in the conclusion unless it -- or at least some term synonymous with it -- had occurred in the premises....Therefore, unless the premises in an argument contain an ethical statement, the conclusion cannot be an ethical statement. So if we assume that the content of science does not already contain ethical statements, then use of the results of science as a set of premises will never yield an ethical statement as a conclusion. (Brandt, Ethical Theory, p. 38-39.)