Essentialism is the view that, for any specific entity (such as an animal, a group of people, a physical object, a concept), there is a set of attributes which are necessary to its identity and function. In Western thought the concept is found in the work of Plato and Aristotle. Platonic idealism is the earliest known theory of how all known things and concepts have an essential reality behind them (an "Idea" or "Form"), an essence that makes those things and concepts what they are. Aristotle's Categories proposes that all objects are the objects they are by virtue of their substance, that the substance makes the object what it is. The essential qualities of an object, so George Lakoff summarizes Aristotle's highly influential view, are "those properties that make the thing what it is, and without which it would be not that kind of thing". This view is contrasted with non-essentialism, which states that, for any given kind of entity, there are no specific traits which entities of that kind must possess.