A proposition is content about which one can assert that it obtains, deny that it obtains, or consider it possible. In a modal statement, a proposition makes it possible to distinguish what is being considered from how it is being considered.
The Proposition and Its Expression
A sentence is the linguistic form in which a proposition is expressed. Different sentences can express the same content, while one and the same sentence can express different content in different circumstances. For example, the content of “I am here” depends on who says it and where. Separating a proposition from the form of a sentence does not mean that the proposition can always be determined without context.
A proposition is also not identical to a fact or situation. The content “the door is open” remains a proposition even when the door is closed. A single situation can be described by different propositions, and a single proposition can encompass several events or relations. Therefore, a proposition cannot be assumed in advance to be the smallest unit of a scenario.
Proposition and Modality
The statements “the door is open,” “it is possible that the door is open,” and “it is necessary for the door to be open” allow us to retain the same content under consideration while assigning different modal assessments. Possibility and necessity have meaning only relative to specified conditions: what counts as an admissible course of events, what is known to the subject, or what is required by a rule. The evaluation of a modal statement depends on the choice of these conditions.
The scope of a modality can extend beyond a single event: “It is possible that someone will open the door after the signal and people will leave” refers to compound content. In expressing an obligation, it also matters to whom and what action is prescribed; “the hero is obliged to open the door” is not equivalent to claiming that the door will inevitably open.
A proposition differs from a thesis neither in size nor in truth value. A proposition characterizes content that can be considered and evaluated; a thesis characterizes the position of that content in the movement of thought and argumentation. The same content may be formulated as a thesis and subsequently become the object of modal consideration.
