At least since the time of Aristotle there has been a tremendous fascination in philosophy with the nature of concepts and universals. What kind of "entity" is a concept such as "horse"? Such abstractions do not designate any particular individual in the world, and yet we can scarcely imagine being able to comprehend the world without their use. Does the concept "horse" therefore have an independent existence outside of the mind? If it does, then what is the locus of this independent existence? The question of locus was an important issue on which the classical schools of Plato and Aristotle famously differed. However, they remained in agreement that universals "did" indeed have a mind-independent existence. There was, therefore, always a "fact to the matter" about which concepts and universals exist in the world.