What Is a Proposition?

William J. Rapaport

Department of Computer Science and Engineering,
Department of Philosophy,
and Center for Cognitive Science
State University of New York at Buffalo,
Buffalo, NY 14260-2000

1. Propositions are NOT prEpositions!

2. Some people consider propositions to be the meanings of sentences, and, in particular, the common meanings of "synonymous" or mutually translatable sentences.

   So, e.g., both the English sentence

   "It's snowing."

   and the French sentence

   "Il neige."

   presumably "mean the same thing", and the thing that they both mean is a proposition. (Of course, that doesn't tell you very much about what a proposition is.)

3. Some people consider propositions to be the bearers of truth values. I.e., the things that are properly considered to be "true" or "false" are propositions, not sentences.

   Note that this is potentially inconsistent with the previous view of what propositions are: Truth (and falsity) are semantic notions, whereas sentences are syntactic things. On the previous view, propositions are semantic things, too (since they are the meanings of sentences). So, to say that propositions are the bearers of truth values is, potentially, to confuse syntax with semantics.

4. Some people consider propositions to be the objects of knowledge and belief. I.e., whenever you say that you (or someone else) knows or believes something, that which they know or believe is a proposition. So, e.g., if I believe that it is snowing, then the object of my belief, viz., that it is snowing, is a proposition. (This may or may not be consistent with either of the above two views of what propositions are.)

5. Bertrand Russell claimed that propositions consist of the objects and properties that they are "about". So, e.g., the proposition
   Snow is white

   would consist, on this view, of snow and of the property of being white.

   Note, by contrast, that the sentence

   "Snow is white."

   consists of the word (or noun phrase) "snow" and the expression (or verb phrase) "is white".

   So, this Russellian view makes propositions to be something like things in the world on a par with things like snow and properties like being white.

6. For further reading:
   • Fitch, Greg (2002), "Singular Propositions", in Edward N. Zalta (ed.), Stanford Encyclopedia of Philosophy

   • King, Jeffrey C. (2001), "Structured Propositions", in Edward N. Zalta (ed.), Stanford Encyclopedia of Philosophy

   • Shapiro, Stuart C. (1993), "Belief Spaces as Sets of Propositions", Journal of Experimental and Theoretical Artificial Intelligence 5(2&3): 225-235.