The "Categories" is an ancient sub-text from Greek philosopher Aristotle's text 'Organon' that enumerates all the possible kinds of things that can be the subject or the predicate of a proposition. The work is brief enough to be divided, not into books as is usual with Aristotle's works, but into fifteen chapters. 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. They are "perhaps the single most heavily discussed of all Aristotelian notions".