Aristotle's Categories is a singularly important work of philosophy. It not only presents the backbone of Aristotle's own philosophical theorizing, but has exerted an unparalleled influence on the systems of many of the greatest philosophers in the western tradition. The Categories is a text from Aristotle's Organon that enumerates all the possible kinds of things that can be the subject or the predicate of a proposition. They are "perhaps the single most heavily discussed of all Aristotelian notions". The Categories places every object of human apprehension under one of ten categories. Aristotle intended them to enumerate everything that can be expressed without composition or structure, thus anything that can be either the subject or the predicate of a proposition.