In short, it is never possible to derive an “ought” from an “is,” or in other words a normative standard of action and behavior from an observable property of the universe. David Hume was the first known philosopher to have this insight. While his observation has been challenged by many people who came after him, it has never been successfully refuted.

Hume’s point stands even though in some situations defined ahead of time by social convention, an “is” does create an “ought,” i.e., the nature of the situation dictates what ought to be done by each party to that situation. The institution of promising or contracting comes to mind. However, there is no duty to participate in the institution of promising/contracting, and whether one ought to keep one’s promises or continue to participate in the institution of promising/contracting after first doing so is a normative question of behavior that can only be answered by reference to moral norms and not by reference to the conventions of the institution of promising/contracting, and here as in all other areas of moral concern there is no objective basis for any moral norms or values that might apply to the situation. In other words, even if there is a contractual obligation to fulfill one’s end of the bargain derived from the nature of the institution of contracting, there is no evidence that one has a moral duty to abide by the contract and actually fulfill one’s end of the bargain. The question of moral duty in this situation is an entirely separate question from what the institution of contracting entails.

To believe it is possible to derive an “ought” from an “is” is to commit the naturalistic fallacy, or the fallacy of stating that because something is natural or the “way things are,” we should act in accordance with that thing or seek that thing as our goal.

A common form of the naturalistic fallacy is the argument that people should act or seek to act a certain way because evolution or biology has made people inclined to act that way. The problem with such a claim is that the mere fact that people have certain inclinations due to their genetic heritage does not provide the slightest reason to believe that people ought to act in accordance with those inclinations or seek the goals those inclinations lead them to have.