Abstract

Analytical tools that give precision to the concept of "independence of syntax" are developed in the form of a series of substitutivity principles. These principles are applied in a study of the rôle of language in belief revision theory. It is shown that sets of sentences can be used in models of belief revision to convey more information than what is conveyed by the combined propositional contents of the respective sets. It is argued that it would be unwise to programmatically restrain the use of sets of sentences to that of representing propositional contents. Instead, the expressive power of language should be used as fully as possible. Therefore, syntax-independence should not be seen as a criterion of adequacy for language-based models of information-processing, but rather as a property that emerges from some but not all the idealization processes through which such models are constructed.