Hume’s Guillotine

Also known as the Is-Ought Problem or Hume’s Law.

The Core Problem

Hume’s Guillotine is the observation that many writers make a leap from descriptive statements (what is) to prescriptive statements (what ought to be) without any logical justification for the shift.

• Descriptive: “Humans are naturally selfish.” (is)
• Prescriptive: “Therefore, humans ought to act selfishly.” (ought)

Origin

Introduced by David Hume in his work A Treatise of Human Nature (Book III, Part I, Section I, 1739).

The Gap

Hume argued that there is a fundamental difference between these two types of statements:

1. Facts: Statements about how the world exists (is).
2. Values: Statements about how the world should be (ought).

He famously noted that “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.”

Implications

• Moral Philosophy: Suggests that ethics cannot be based solely on factual observations or scientific data.
• Logical Inference: An ethical argument is considered logically invalid if it lacks an “ought” premise but reaches an “ought” conclusion.
• Bridge Premises: To move from “is” to “ought,” one must implicitly or explicitly introduce a moral principle or premise (e.g., “we should do what is natural”).

---