The ancestor of categorical and category has been important in logic and philosophy since the days of Aristotle. Both English words derive from Greek katēgoria, which Aristotle used to name the 10 fundamental classes (also called "predications" or "assertions") of terms, things, or ideas into which he felt human knowledge could be organized. Ironically, although those categories and things categorical are supposed to be absolute and fundamental, philosophers have long argued about the number and type of categories that exist and their role in understanding the world. High-level philosophical disputes aside, the word categorical continues to sometimes describe an absolute assertion, one that involves no conditions or hypotheses—for example, the statement "all humans are mortal."