The meaning of an unmodalized independent declarative sentence is the assertion of a proposition. The speaker intends to establish this proposition in the universe of discourse so it is not controversial between him and his interlocutor. Consider .

The speaker of affirms what he takes to be a fact. His interlocutor may reply either of .

In answering a, the interlocutor attributes himself a propositional attitude which is factive with respect to its object. He thereby accepts the state of the universe of discourse as it is after the utterance of and confirms it. In answering b instead, he calls the establishment of this proposition in question by treating it as a hypothesis. Upon this answer, the first speaker may get indignant and reply: No, I tell you, she has! The complement clause of the verb know involves a factive presupposition; the complement clause of hope does not.

Since a fact can be a referent, is is taken up by a coreferential anaphoric pronoun. This is it in .a. Since a proposition is just a piece of meaning, it is taken up by a proform that is an abbreviated representation of what propositional content is currently accessible. This is so in #b (Halliday & Hasan 1976, ch. 3.4).

Halliday, Michael A.K. & Hasan, Ruqaiya 1976, Cohesion in English. London: Longman.

Kiparsky, Paul & Kiparsky, Carol 1970, "Fact." Bierwisch, Manfred & Heidolph, Karl E. (eds.), Progress in linguistics. A collection of papers selected and edited by M.B. & K.E.H. The Hague & Paris: Mouton (Janua Linguarum Series Maior, 43); 143-173.