 This scheme descends from that in Plato, Republic V ad fin., where the objects of knowledge were differentiated from those of belief, and from Republic VI ad fin., where that division is portrayed on a divided line. In the latter passage, Plato seems actually to have four divisions of types of cognition and their objects, but this is notoriously difficult (see Burnyeat 1987), and Xenocrates appears to have rethought it. His tripartite division of objects looks like that in Aristotle, Metaphysics XII 1.