  Bacon presents a detailed classification of  signs[24]  by taking up, combining, and modifying elements of several prior sign typologies. The division of the two main classes of natural and given signs is taken from Augustine, the distinction between necessary and probable signs is borrowed from Aristotle (an. pr. II, 27, 70a3-b5), and their subdivision according to their temporal reference is a traditional element in the theories of the sacramental  sign.[25]