A value theory indicates the characteristics common to values of all kinds, classifies them, and clarifies the meaning of value-propositions. The kinds or "realms" of value are always said to include moral and aesthetic values, but other kinds are usually mentioned also. For instance, Paul Taylor (1925–) lists six others: intellectual, religious, economic, political, legal, and customary realms of value. All value theorists claim that even though there are striking or important differences among kinds of value, their similarities are more fundamental. As Ralph Barton Perry (1876–1957) puts it, value theory pulls concerns "dispersed among the several philosophical and social sciences" into a single "comprehensive inquiry" in which these various pursuits are "unified and distinguished," so as "to bring to light the underlying principles common to these sciences, and then to employ this principle for the purpose of arbitrating...