wherever there is pain there must be imperfection. Another plea is the necessity of pain as a punishment for crime, or, more generally, as a result of moral freedom. Such an argument is only open to the believers in free-will. A world of free and responsible agents, they urge, is infinitely more valuable than a world of automata; and it is not too dearly purchased even at the cost of such suffering as we witness. The argument is not very convincing; for liberty of choice {61} in a painless world is quite conceivable. But, be it a good or bad argument, although it might appeal to Voltaire, who believed in free-will, it could not decently be used by Leibniz, who was a determinist of the strictest type. To make this clear we must now turn to his metaphysical system. Bacon, Descartes, and Spinoza, disagreeing widely on other subjects, were agreed in discountenancing the study of final causes: Bacon, apparently, from dislike of the idea that the perfect adaptation of all things to the service of man rendered superfluous any efforts to make them more serviceable still; Descartes from his devotion to the mathematical method which was more applicable to a system of mechanical causation; Spinoza for the same reason, and also from his disbelief in a personal God. Leibniz, on the contrary, felt deeply impressed by a famous passage in Plato's _Phædo,_ where Socrates, opposing the philosophy of teleology to the philosophy of mechanism, desiderates an explanation of nature as designed with a view to the highest good. But Leibniz did not go so far as Plato. Mediating between the two methods, he taught that all is done for the best, but also that all is done through an unbroken series of efficient causes. At the same time, these causes are only material in appearance; in reality they are spiritual beings. There is no such thing as dead matter; the universe consists of living forces all through. The general idea of force probably came from that infinite Power of which, according to Spinoza, the whole universe is at once the product and the expression; or it may have been suggested by Plato's incidental identification of Being with Action. But Leibniz found his type of force in human personality, which, following the lead of Aristotle {62} rather than of Plato, he conceived as an Entelechy, or realised Actuality, and a First Substance. After years of anxious reflection he chose the far happier name of Monad, a term originally coined by Bruno, but not, as would appear, directly borrowed from him by the German metaphysician.