 But closer inspection of this method reveals some significant concerns. To start with, when a distinction is taken as basic and unanalyzable, one typically has to offer some intuitive instances of the primitive predicates. But it is not always so easy to do this. For example, when mathematicians take set and membership as primitives and then assert some principles of set theory, they often illustrate their primitives by offering some examples of sets, such as The Undergraduate Class of 2020 or The Ethics Committee, etc. But these, of course, aren’t quite right, since the members of the class and committee may change while the class and committee remain the same, whereas if the members of a set change, one has a different set. A similar concern affects the present proposal. If one offers sets or the characters of the Sherlock Holmes novels as examples to help motivate the primitive concept abstract object, then one has to wonder about impure sets such as the unit set whose sole member is Aristotle (i.e., \(\{\textrm{Aristotle}\}\)) and the object London that appears in the novels.