Quine [1969] uses a notion of ``eternal sentence'', essentially one that doesn't depend on context. This seems a doubtful idea and perhaps incompatible with some of Quine's other ideas, because there isn't any language in which eternal sentences could be expressed that doesn't involve contexts of some sort. We want to modify Quine's idea into something we can use.
The usefulness of eternal sentences comes from the fact that ordinary speech or writing involves many contexts, some of which, like pronoun reference, are valid only for parts of sentences. Consider, ``Yes, John McCarthy is at Stanford University, but he's not at Stanford today''. The phrase ``at Stanford'' is used in two senses in the same sentence. If the information is to be put (say) in a book to be read years later by people who don't know McCarthy or Stanford, then the information has to be decontextualized to the extent of replacing some of the phrases by less contextual ones.
The way we propose to do the work of ``eternal sentences'' is called relative decontextualization. The idea is that when several contexts occur in a discussion, there is a common context above all of them into which all terms and predicates can be lifted. Sentences in this context are ``relatively eternal'', but more thinking or adaptation to people or programs with different presuppositions may result in this context being transcended.