 According to the way of conflation, the abstract/concrete distinction is to be identified with one or another metaphysical distinction already familiar under another name: as it might be, the distinction between sets and individuals, or the distinction between universals and particulars. There is no doubt that some authors have used the terms in this way. (Thus Quine 1948 uses ‘abstract entity’ and ‘universal’ interchangeably.) This sort of conflation is however rare in recent philosophy.