  Philosophers speak about categories in many different ways. There is one initial, and rather substantial, difference between philosophers who allow a very large number of categories and those who allow only a very small number. The first include among categories such different things as human, green, animal, thought, and justice; the second speak only of very general things such as substance, quality, relation, and the like, as categories. Among twentieth-century authors who allow many categories is Gilbert Ryle (b. 1900, d. 1976). Roderick Chisholm (b. 1916, d. 1999) is an example of those who have only very few. Medieval authors follow Aristotle's narrow understanding.