Hinge Propositions

Doubt requires a setting. To doubt whether there are physical objects, or whether I have ever had a body, is to attempt doubt at a level where the concept of doubt loses its grip. Genuine doubt is doubt about something specific, against a background of things not doubted. "I have two hands" functions differently from "I have two coins in my pocket": the latter I can be wrong about and verify; the former is not the kind of thing I discover to be true — it is what I am certain of before any discovering begins.

Hinge propositions are not outside the language game but at its foundation. They are, Wittgenstein says, like the axis around which a body rotates: it must be fixed for the movement to occur, but it is not itself in motion. The propositions "The earth has existed for more than a hundred years," "I have never been on the moon," "Physical objects exist" — none of these are conclusions of inference. They are presuppositions of the forms of reasoning that would produce such conclusions.

Wittgenstein is careful to say that we do not know our hinge propositions in the ordinary sense. Knowledge implies the possibility of doubt, the having of evidence, the capacity to be wrong. Hinge propositions are held in place by something prior to knowledge: a practical certainty embedded in action and form of life. "I have two hands" is not a proposition I believe on evidence — it is a proposition whose denial would signal not doubt but mental disorder. This is not scepticism's victory; it is scepticism's dissolution.

The concept of hinge propositions is introduced at §§341–343 of On Certainty, with the pivotal image of the door hinge at §341. The book's discussion is continuous with Wittgenstein's response to G.E. Moore's "Proof of an External World" and "Certainty," which begins in the opening passages.