 The medieval synthesis Thomas Aquinas (1224–74) forged between Christian theology and Aristotle’s science and metaphysics set the terms for the early modern causation debate. Aristotle (384–322 BCE) drew an absolute categorical distinction between scientific knowledge (scientia) and belief (opinio). Scientific knowledge was knowledge of causes and scientific explanation consisted in demonstration—proving the necessary connection between a cause and its effect from intuitively obvious premises independently of experience.