Valid concepts, as we have seen, are based on objective differences of kind among the units they subsume, differences which must be grasped in order to understand reality. It is not sufficient for a concept to be merely "useful," because utility is always relative to a particular purpose, and cognition is only one of the many purposes pursued by human beings. Often we classify items for ends other than cognition. Sometimes those ends are quite innocuous; for example, we may group a number of conceptually disparate items together into a shopping list. A shopping list, however, does not constitute a concept. We should be especially wary of a shopping-list approach to moral and political concepts: the mere fact that we desire (or abhor) a set of things does not suffice to establish that set as a valid concept.
Pseudo-conceptual groupings of items can also be used to sow deliberate confusion, to attain or consolidate political power, or simply for unconscious evasion. Often terms such as "public interest," "societal need," "rights," and "freedom" are associated with such groupings. We will not consider such groupings as proper concepts in this course, although some of these terms will be identified with true concepts.