=116.= Similar concessions to his opponents mark his treatment in detail of ethics. Thus he takes from Aristotle the view that ‘virtue is a mean between two vices’; and this doctrine, so alien from true Stoic principle, forms the basis of the treatment which we find adopted in the _de Officiis_. The theory of the four ‘cardinal virtues,’ Wisdom, Justice, Courage, and Soberness, was probably common property at this time; but whereas in Cynism Courage and in the earlier Stoicism Wisdom are the dominant virtues, in the theory of Panaetius Soberness, identified with decorum, far exceeds the rest in practical importance. Thus the triumph won by Panaetius for the name of Stoicism was purchased by the sacrifice not only of its physics, but very largely of its ethics also; and the success of the new system might not unfairly be described as a victory of literature over logic, of reasonableness over reason, and of compromise over consistency. However this may be, Panaetius undoubtedly succeeded in presenting Greek philosophy to his Roman friends in a form in which it recommended itself alike to their reasoning powers and to their moral sense. [Sidenote: Posidonius.] =117.= The virtual, though not the nominal, successor of Panaetius was POSIDONIUS of Rhodes[31] (circ. 135-51 B.C.[32]), who after studying under Panaetius at Athens travelled widely, finally settling at Rhodes, and there took an active part in political life. Like his master, he was a devoted student of Plato, and he wrote a commentary on the _Timaeus_. In this commentary he developes a new theory of the universe, which he asserts to be that which Plato had learnt from the Pythagoreans, and to be at root the same as that taught by the Stoics. The starting-point is the μονάς or unit; from this are evolved the numbers and the elements by a principle of flux, as in the system of Heraclitus[33]. The unity and the first of the numbers, the two, differ as force and matter; so that the dualism of Aristotle is here definitely subordinated to a supreme monism. This study of Posidonius is therefore incidentally of high importance as a side-light on Stoic metaphysics and cosmology. In addition he wrote on almost all the principal divisions of philosophy, thus acquiring a brilliant reputation, particularly in the eyes of the philosophic nobles of Rome. Cicero made his acquaintance at Rhodes in 78 B.C., and refers to him more often in his works than to any other of his instructors[34]. Pompey, in the midst of his eastern campaigns, put himself to much trouble to visit him[35]. Amongst his Roman visitors and admirers were also Velleius, Cotta, and Lucilius[36]. A century later, Seneca looked back to him as one of those who had made the largest contribution to philosophy[37]. [Sidenote: His teaching.]