Full Idea
A minimal theory of propositions can make do with just two primitive properties: a property of consistency applied to sets of propositions, and a property of truth applied to propositions.
Gist of Idea
A theory of propositions at least needs primitive properties of consistency and of truth
Source
Robert C. Stalnaker (Mere Possibilities [2012], 2)
Book Reference
Stalnaker,Robert C.: 'Mere Possibilities' [Princeton 2012], p.24
A Reaction
I would have thought a minimal theory would need some account of what a proposition is supposed to be (since there seems to be very little agreement about that). Stalnaker goes on to sketch a theory.