Part 23 of Red Herrings covers still more responses to arguments that distract from the argument rather than address it directly. This week, the is-ought problem.
The “is-ought problem” is also known as Hume’s Law or Hume’s Guillotine, first articulated by Scottish philosopher David Hume in his 1739 work A Treatise of Human Nature.
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 ways of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when all of a sudden I am surprised 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 seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it.As in the case of many logical fallacies, it’s not necessarily the case that “is” precludes “ought,” but rather that “is” doesn’t constitute a sufficient proof by itself. To reach a conclusion of “ought” requires additional argument.
The problem is easier in goal-setting than in morality. For example, if you want to win a race, then you ought to run quickly. However, whether you ought to want to win in the first place is a different question.