||The category of stuff is notoriously vague, due in part to the unclear and ill-defined contrast between 'stuff' and 'things' . In particular, while there appears to be a loose and informal consensus within philosophy that 'stuff' is to be treated as an extremely general concrete noun - to be applied to substances like sugar, flour, dough and plutonium (but not to the extension of such nouns as 'furniture') - and to be juxtaposed to 'things', as in some of Quine's writings, there is little consensus as to the extension of 'things'. For some, 'things' should here be understood to cover, roughly, Aristotle's substances - substances in that very different sense of being discrete, concrete, organised individuals consisting of both form and matter, stuff and structure. For others, 'things' is understood more generally as 'objects' in the traditional purely logical sense - roughly, whatever counts as the value of a variable - and the question then arises of whether the initial dichotomy can be preserved, or not. It is here that the nature of the metaphysical dichotomy, if such it be, meets the semantical dichotomy of so-called mass and count nouns. Some concrete nouns that are semantically mass are, in virtue of their particular semantic character, nouns for things described collectively. Thus 'furniture' denotes not stuff but things, while other mass nouns such as 'soup' are naturally words for stuff. However, if 'things' is construed purely logically, as with Quine or Witttgenstein, then it is often argued that mass nouns too are words for things - 'quantities', 'parcels', 'portions', etc. of stuff. Stuff on such accounts is often theorised in terms of a mereology, and here again, the fields of metaphysics and semantics virtually coincide. More recently, and consequent on studies of non-singular reference and predication, the question of whether our standard 'singularist' logic is suited to the analysis of mass nouns in general, and words for stuff in particular, has been pressed. Here, the logico-semantic writings of George Boolos and Tom McKay on plurals have acquired a certain relevance, and figure in the more recent logico-metaphysical writings of Laycock on the topics of things or objects, stuff, and mass nouns. The overlap between this topic and related issues in the philosophy of language is represented in the entry on mass nouns and count nouns.