 Thus Avicenna arrives at the idea of an absolute cause which is the cause of all things: the series, its units and the relations that bind them to one another. One might posit the existence of something that causes some units and not others, but this would certainly not be the absolute cause, which is a cause that cannot be caused in any way. It is an extreme (ṭaraf) and therefore neither an intermediate element nor an effect. So, every chain (silsila) needs a cause external to it: an extreme—the Necessary Existent Principle—which is not caused and therefore gives a foundation to the causal chain without being part of it. Indeed, in the Ilāhiyyāt of Kitāb al-Šifā Avicenna explicitly states that the flow of being is “distinct” (mubāyin) from the Principle (Ilāhiyyāt, IX, 4, 403, 13).