entia non grata

In philosophy, "entia non grata" refers to entities that a philosopher would prefer not to admit into their worldview, often due to their perceived strangeness or complexity. Debates about universals, which are abstract concepts or properties, often involve discussions of "entia non grata".1

Philosophers like W.V.O. Quine and Nelson Goodman had differing views on which entities were more problematic. Quine, for instance, reluctantly accepted classes because they are necessary for mathematics used in physics, but he rejected universals. Goodman, however, found classes more distasteful than certain universals, illustrating how judgments about what is "strange" can vary significantly among philosophers.1

The core of these debates often revolves around whether certain abstract entities, like classes or universals, are necessary to explain reality or if they can be treated as fictions. There is little agreement on where these entities should be placed on a philosopher's list of "entia non grata".1