The true ground of the distinction is, in fact, linguistic; it is derived from syntax. There are proper names, adjectives, and relation-words; we may say ‘John is wise, James is foolish, John is taller than James.’ Here ‘John’ and ‘James’ are proper names, ‘wise’ and ‘foolish’ are adjectives, and ‘taller’ is a relation-word. Metaphysicians, ever since Aristotle, have interpreted these syntactical differences metaphysically: John and James are substances, wisdom and folly are universals.

Bertrand Russell, History of Western Philosop…, loc. 732