 By the above criteria, a definition of “sexual activity” is hard to find. One crucial reason might be that what we commonly think is a sexual act does not depend on one criterion: behavior, intentions, contact with body parts, etc., play a role depending on the context. Another reason might be that there are many concepts closely related to each other that nonetheless commonly mean different things. “To have sex” or “to engage in sex” almost always refer to sexual activity with at least one more person, whereas “engaging in a sexual activity)” and “having a sexual experience” do not have this reference, and they are not common expressions. Thus, defining these concepts is tricky if we want the definitions to agree with common linguistic usage, or if we rely on such usage to formulate these definitions. More worrisome, if we need to define these concepts for help with practical, moral, and legal issues, the rift between them and common language should give us pause.