The word "universal" comes from the Latin term universalis meaning "that which pertains to all," that is, they can be applied throughout the universe. The corresponding Greek term usually employed by Plato was eidos or "Idea." Aristotle used the Greek term to kathodos [the whole], which has about the same meaning as the Latin word given above. The word "universal" is related to the concepts of species, genus, and class. It stands in contrast to the terms "particular" and "individual." Thus the word "universal" is related to the simple classification of words as either general or singular. A singular word refers to a specific object, event, or instance of quality. For example, "Ronald Regan", "Los Angeles", "this football game", "this red here" are singular terms. A general word refers to a class or kind of objects, events, or qualities. For example, "Man," "cities," "athletics," "color" are general terms. A general term applies to each member of the class or kind. The word "man" applies to every individual man, "red" to every occurence of that property, and "running" to every instant or event of someone running. General words are indispensable in everyday human communication, as may be seen by trying to say a few sentences without them. Universals are general words. The problem of universals is concerned with the ontological status or mode of being of the referents of general words. This problem arises in connection with general words because they do not designate observable things, events, or qualities. We do not see the referents of general words, but only specific individual instants of them. For example, take the sentence, "Tom is a man." We can see Tom and we can talk him, etc. But we do not with man. No one has ever seen man walking down the street; we only see a man, a specific individual, like Tom. If the referents of general words are not obversables, then what are they?
During the Middle Ages an intense debate took place about the ontological status of general words or universals. Three different solutions were proposed and defended: Realism, Conceptualism, and Nominalism.
Royce does not presume, like Hegel, to deduced all the categories and conceptions of the Absolute in a dialectic. Royce is Kantian enough to admit that detailed information about matters of fact and the general principles of scientific descriptions requires sensuous experience in addition to the categories of the mind. Only some general principles about the nature of reality as a whole can be established a priori; that is, only propositions which cannot be denied without inconsistently assuming them in the very act of denial. Only in this way can we be absolutely certain about the Absolute itself and some related principles of metaphysics, logic and ethics; but for the rest of knowledge, they must depend on observation and experience.