  Another idiom which Quine famously excludes from regimented theory is that of modality, statements that such-and-such must be the case, or cannot be the case, and so on. Such idioms have been the subject of much discussion on the part of Quine and (especially) his critics; the discussion here will be very brief. Technically, there are similarities with the case of belief. There is prima facie violation of extensionality which can, however, be avoided by taking necessity to apply to sentences; some philosophers have claimed that there is a de re sense of necessity which does not lead to even prima facie violations of extensionality. Quine allows that modal terms have a legitimate ordinary language use (‘possible’ is sometimes used to mean something like: we can’t rule it out; see 1966, ch. 10). But his attitude towards the philosophical use of the idea of modality, dividing truths into the necessary and the possible, is far less sympathetic than his attitude towards belief; he is particularly unsympathetic towards the idea of de re necessity, which he sees as requiring “Aristotelian essentialism” (Quine, 1953, 155).