proposition an abstract object said to be that to which a person is related by a belief, desire, or other psychological attitude, typically expressed in language containing a psychological verb (‘think’, ‘deny’, ‘doubt’, etc.) followed by a thatclause. The psychological states in question are called propositional attitudes. When I believe that snow is white I stand in the relation of believing to the proposition that snow is white. When I hope that the protons will not decay, hope relates me to the proposition that the protons will not decay. A proposition can be a common object for various attitudes of various agents: that the protons will not decay can be the object of my belief, my hope, and your fear.
A sentence expressing an attitude is also taken to express the associated proposition. Because ‘The protons will not decay’ identifies my hope, it identifies the proposition to which my hope relates me. Thus the proposition can be the shared meaning of this sentence and all its synonyms, in English or elsewhere (e.g., ‘die Protonen werden nicht zerfallen’).
This, in sum, is the traditional doctrine of propositions. Although it seems indispensable in some form – for theorizing about thought and language, difficulties abound.
Some critics regard propositions as excess baggage in any account of meaning. But unless this is an expression of nominalism, it is confused. Any systematic theory of meaning, plus an apparatus of sets (or properties) will let us construct proposition-like objects. The proposition a sentence S expresses might, e.g., be identified with a certain set of features that determines S’s meaning. Other sentences with these same features would then express the same proposition. A natural way to associate propositions with sentences is to let the features in question be semantically significant features of the words from which sentences are built. Propositions then acquire the logical structures of sentences: they are atomic, conditional, existential, etc. But combining the view of propositions as meanings with the traditional idea of propositions as bearers of truthvalues brings trouble. It is assumed that two sentences that express the same proposition have the same truth-value (indeed, that sentences have their truth-values in virtue of the propositions they express). Yet if propositions are also meanings, this principle fails for sentences with indexical elements: although ‘I am pale’ has a single meaning, two utterances of it can differ in truth-value. In response, one may suggest that the proposition a sentence S expresses depends both on the linguistic meaning of S and on the referents of S’s indexical elements. But this reveals that proposition is a quite technical concept – and one that is not motivated simply by a need to talk about meanings. Related questions arise for propositions as the objects of (propositional) attitudes. My belief that I am pale may be true, yours that you are pale false. So our beliefs should take distinct propositional objects. Yet we would each use the same sentence, ‘I am pale’, to express our belief. Intuitively, your belief and mine also play similar cognitive roles. We may each choose the sun exposure, clothing, etc., that we take to be appropriate to a fair complexion. So our attitudes seem in an important sense to be the same – an identity that the assignment of distinct propositional objects hides. Apparently, the characterization of beliefs (e.g.) as being propositional attitudes is at best one component of a more refined, largely unknown account. Quite apart from complications about indexicality, propositions inherit standard difficulties about meaning. Consider the beliefs that Hesperus is a planet and that Phosphorus is a planet. It seems that someone might have one but not the other, thus that they are attitudes toward distinct propositions. This difference apparently reflects the difference in meaning between the sentences ‘Hesperus is a planet’ and ‘Phosphorus is a planet’. The principle would be that non-synonymous sentences express distinct propositions. But it is unclear what makes for a difference in meaning. Since the sentences agree in logico-grammatical structure and in the referents of their terms, their specific meanings must depend on some more subtle feature that has resisted definition. Hence our concept of proposition is also only partly defined. (Even the idea that the sentences here express the same proposition is not easily refuted.)
What such difficulties show is not that the concept of proposition is invalid but that it belongs to a still rudimentary descriptive scheme. It is too thoroughly enmeshed with the concepts of meaning and belief to be of use in solving their attendant problems. (This observation is what tends, through a confusion, to give rise to skepticism about propositions.) One may, e.g., reasonably posit structured abstract entities – propositions – that represent the features on which the truth-values of sentences depend. Then there is a good sense in which a sentence is true in virtue of the proposition it expresses. But how does the use of words in a certain context associate them with a particular proposition? Lacking an answer, we still cannot explain why a given sentence is true. Similarly, one cannot explain belief as the acceptance of a proposition, since only a substantive theory of thought would reveal how the mind ‘accepts’ a proposition and what it does to accept one proposition rather than another. So a satisfactory doctrine of propositions remains elusive.
See also ABSTRACT ENTITY, INDEXICAL , INTENTIONALITY , MEANING , PROPERT. S.J.W.