Does the idea of expressive power make sense when talking about natural languages? One will only be tempted to use that vocabulary, it seems, if one is already viewing natural languages in terms of first-order (or higher) logic, that is, viewing natural languages as containing terms and predicates with grammatical sentences as wffs. (Maybe, a slightly more nuanced way of putting the view is that the structure of first-order logic faithfully and straightforwardly represents that of natural languages; I don’t want to rule out the idea of using first-order logic to represent natural languages, since ,e.g. HPSG does it for syntax; although the FOL representation of English by FOL in HPSG looks nothing like English and is pretty well unreadable.) A few authors use this vocabulary: Brandom, Dummett, Sellars. In order to use the notion of expressive power, we have to a well-defined idea of wffs for a language and ways of comparing what is expressible in one language and another. What will be at issue here won’t be different languages in the sense of English and Japanese, but different languages in the sense of fragments of English, say, one with ‘and’ and one with ‘and’ and ‘not’. While there is nothing wrong with viewing things like this when one is explicit about the regimentation, it is a little misleading.