Propositional meaning is also referred to as the sentence meaning. Knowing the meaning of a sentence is knowing what the sentence is all about, and what, who, where, when and how are involved. The following sentences differ in their structure, but they share the same prepositional content:

　　I regard her as being less than bright.
　　She is regarded as being less than bright by me.
　　She strikes me as being less than bright.

In other words, the above three sentences can be used to paraphrase each other's propositional meaning, and therefore paraphrasing becomes a very useful device to help us to check our understanding of the propositional content of a sentence.