 For example, pure sets are paradigm examples of abstract entities. But the case of impure sets is far from clear. Consider the unit set whose sole member is Joe Biden (i.e., {Joe Biden}), the Undergraduate Class of 2020 or The Ethics Committee, etc. They are sets, but it is not clear that they are abstract given that Joe Biden, the members of the class and committee are concrete. Similarly, if one offers the characters of Sherlock Holmes stories as examples to help motivate the primitive concept abstract object, then one has to wonder about the object London that appears in the novels.