Xenocrates (/zəˈnɒkrəˌtiːz/; Greek:Ξενοκράτης; c. 396/5 – 314/3 BC<) of Chalcedon was a Greek philosopher, mathematician, and leader (scholarch) of the Platonic Academy from 339/8 to 314/3 BC. His teachings followed those of Plato, which he attempted to define more closely, often with mathematical elements. He distinguished three forms of being, the sensible, the intelligible, and a third compounded of the two, to which correspond respectively, sense, intellect and opinion. Unity and duality he considered to be gods which rule the universe, and the soul is a self-moving number. God pervades all things, and there are daemonical powers, intermediate between the divine and the mortal, which consist in conditions of the soul. He held that mathematical objects and the Platonic Ideas are identical, unlike Plato who distinguished them. In Ethics, he taught that virtue produces happiness, but that external goods can minister to it and enable it to effect its purpose.