Philosophy In Seconds

56. Hume’s Guillotine, or the Is-Ought Problem


In the middle of the 18th Century, the Scottish philosopher David Hume came up with a radical idea, which would change moral reasoning forever. In his landmark work “A Treatise of Nature”, Hume treated many subjects with his ruthless skepticism and drastically altered our intuitions of identity, knowledge and morality. Hume noticed that in all of the moral systems he had observed there was one vital and defeating flaw and this is referred to today as the Is-Ought Problem.

Generally, there are two types of statements that you can make about the world; they are either descriptive, (i.e: how the world is) or prescriptive (i.e: how the world should be). What Hume observed was our remarkably common tendency to derive how we ought to behave from how the world is. For instance:

Premise: Marijuana has always been illegal.
Conclusion: Therefore, we ought to ensure that marijuana is illegal.

The premise is true, but does it follow that the conclusion is true? Not necessarily. If we look closely at the argument above, we have a descriptive premise which yields a prescriptive conclusion, with nothing tying them together. Therefore, Hume’s guillotine logically severs the connection between descriptive and prescriptive statements since there is no logically coherent way to bridge this gap. Even if we try to bridge this gap with any form of rhetoric we still cannot overlook that are we trying to generate a moral imperative from a description of a particular state of affairs.

This does seriously question our morality significantly, since we tend to reason about how things currently are to decide what we should or should not do. Some contemporary responses suggest that we can use induction to bypass the is-ought problem. For instance, conducting numerous experiments and using the frequency of a result to reason about what we should do. Yet, it seems we must then arbitrarily decide how much evidence we require to validly reason from the how world is. In any case, Hume himself did not suggest with the Is-Ought Problem that facts are not at all connected to obligations, but that through his observations a ‘logically dirty’ step was being made where an ethical principle might clean up someone’s argument. Either way this dichotomy between fact and value is one philosophers still have to wrestle with in gaining moral knowledge and it should always be taken into consideration. Or should it?