We say of a sentence or a sentence utterance that it is context-sensitive when its truth or falsehood depends on certain elements that only the context of utterance can reveal. Sentence utterances that contain indexical expressions such as "here', "now', "yesterday', "she' or "this' are such that what they mean — and what they refer to — can shift from context to context. What "It is windy today' refers to, that is, the weather on the day it is uttered, at the place it is uttered, will sometimes make it false, sometimes make it true — since it can be uttered on different more or less windy days or in different more or less windy places. By contrast, an utterance of "2 + 2 = 4' is typically considered not to be context-sensitive since it is true no matter what the context in which it is uttered. On Bolzano's account, context-sensitive sentences are semantically underdetermined: they do not express the proposition that forms their content "completely". Only sentences that are "eternally" or "immutably" true (or false), that is, only sentences that are not context-sensitive express their content completely in the sense that is relevant to Bolzano. The purpose of analysis in his theory is to reveal the "Sinn" of expressions (cf. 1837, §285, 67).