Hume's Is-Ought Problem: The Fact-Value Distinction in Moral Philosophy

David Hume’s famous observation that one cannot derive an “ought” from an “is” — what is now known as the “is-ought problem” or the “fact-value distinction” — is one of the most influential and controversial claims in the history of moral philosophy. The claim has been the subject of intense debate ever since its articulation, and it remains a central reference point for contemporary discussions of the nature of morality, the possibility of ethical knowledge, and the relationship between fact and value.

The Original Statement

Hume’s statement of the is-ought problem comes in his Treatise of Human Nature (1739–1740), in the course of his discussion of moral philosophy. He writes: “In every system of morality, which I have hitherto met with, I have always 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 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 shou’d be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it.”

The basic claim is that the inference from descriptive premises (“is”) to normative conclusions (“ought”) is not self-evident. The descriptive premises tell us about the way the world is; the normative conclusions tell us about the way the world ought to be. There is a logical gap between these two kinds of claims, and the gap cannot be bridged by any amount of descriptive reasoning.

The Implications

The is-ought problem has had a profound influence on the subsequent development of moral philosophy. The most important implications are the following.

First, the problem challenges the possibility of deriving moral conclusions from non-moral premises. If the inference from “is” to “ought” is not self-evident, then moral conclusions cannot be derived from purely factual premises. Moral conclusions require moral premises, and the proper foundation of morality is a question that cannot be answered by factual reasoning alone.

Second, the problem challenges the possibility of a purely rational foundation for morality. If moral conclusions cannot be derived from factual premises, then morality is not a matter of rational insight into the nature of the universe. The proper foundation of morality must lie elsewhere — in sentiment, in tradition, in divine command, or in some other non-rational source.

Third, the problem has implications for the relationship between moral philosophy and the natural sciences. If the is-ought problem is correct, then the natural sciences, which are concerned with the description of natural phenomena, cannot by themselves provide a foundation for morality. The natural sciences can tell us about the way the world is, but they cannot tell us about the way the world ought to be.

The Responses

Hume’s claim has been the subject of intense debate ever since its articulation, and a number of responses have been developed.

The first response is that Hume’s claim is not actually a problem. The defenders of this view argue that the inference from “is” to “ought” is not as problematic as Hume suggests. The description of a particular state of affairs, properly understood, may already contain implicit evaluative assumptions. The inference from “is” to “ought” may be justified by an appeal to the proper description of the situation, including the interests, the needs, and the values of the persons involved.

The second response is that Hume’s claim is a problem, but it is a problem that can be solved. The defenders of this view argue that there are moral premises that can be used to derive moral conclusions from factual premises. The proper foundation of morality is found in the moral sentiments, in the social contract, in the principles of practical reason, or in some other normative framework that provides the premises for the inference from “is” to “ought.”

The third response is that Hume’s claim is a real problem, and it cannot be solved. The defenders of this view argue that the is-ought problem shows that morality is not a matter of rational insight but of sentiment, tradition, or some other non-rational source. The proper response to the is-ought problem, on this view, is to acknowledge the limits of moral reasoning and to accept the role of sentiment, tradition, or some other non-rational source in the foundation of morality.

The Legacy

Hume’s is-ought problem has had a profound influence on the development of modern moral philosophy. The problem is one of the central references for the modern debate about the nature of morality, the possibility of ethical knowledge, and the relationship between fact and value. The contemporary debate about the is-ought problem is shaped by a number of new developments, including the rise of moral psychology, the development of the cognitive sciences, and the various challenges to the traditional framework of moral philosophy from contemporary thinkers in the analytic and Continental traditions.

Further Reading

• The Stanford Encyclopedia of Philosophy (plato.stanford.edu), relevant entry
• The Cambridge Companion to [Thinker] (Cambridge University Press)
• Isaiah Berlin, Four Essays on Liberty (1969)