Mystics differ radically, however, in their claims about extrasensory realities. Ancient and Hellenistic philosophers offered three examples of the reality of the extrasensory: the numbers and mathematical formulas of Pythagoras; the forms (or “ideas”) of Plato and the universals (substantial and accidental forms) of Aristotle; and the Stoic concept of the lekton, or “saying.” Thus, a number or a mathematical formula exists or is true objectively, whether or not it is known by any person.