Full Idea
A proposition may be defined as: what we believe when we believe truly or falsely.
Gist of Idea
A proposition is what we believe when we believe truly or falsely
Source
Bertrand Russell (On Propositions: What they are, and Meaning [1919], p.285)
Book Reference
Russell,Bertrand: 'Logic and Knowledge', ed/tr. Marsh,Robert Charles [Routledge 1956], p.285
A Reaction
If we define belief as 'commitment to truth', Russell's last six words become redundant. "Propositions are the contents of beliefs", it being beliefs which are candidates for truth, not propositions. (Russell agrees, on p.308!)
Related Idea
Idea 20311 An idea involves affirmation or negation [Spinoza]