A class of basic particulars, in Strawson's terminology, is a class of particulars such that 'as things are, it would not be possible to make all the identifying references which we do make to particulars of other classes, unless we made identifying references to particulars of that class, whereas it would be possible to make all the identifying references we do make to particulars of that class without making identifying reference to particulars of other classes' (pp. 38-9).