There are certain absurd opinions which we are sure we have been taught, although, when put to it, we find it hard to name the teacher. Among them is something of this sort. 'Leibniz was a scholarly and sympathetic thinker. He had more sense of history than his contemporaries, and he was instinctively eclectic. He believed he could learn something from each of his great predecessors. We see him reaching back to cull a notion from Plato or from Aristotle; he even found something of use in the scholastics. In particular, he picked out the Aristotelian "entelechy" to stop a gap in the philosophy of his own age.' What this form of statement ignores is that Leibniz _was_ a scholastic: a scholastic endeavouring, like Descartes before him, to revolutionize scholasticism. The word 'entelechy' was, indeed, a piece of antiquity which Leibniz revived, but the thing for which it stood was the most familiar of current scholastic conceptions. 'Entelechy' means active principle of wholeness or completion in an individual thing. Scholasticism was content to talk about it under the name of 'substantial form' or 'formal cause'. But the scholastic interpretation of the idea was hopelessly discredited by the new science, and the scholastic terms shared the discredit of scholastic doctrine. Leibniz wanted a term with a more general sound. 'There is an _X_', he wanted to say, 'which scholasticism has defined as substantial form, but I am going to give a new definition of it.' Entelechy was a useful name for _X_, the more so as it had the authority of Aristotle, the master of scholasticism. Under the name of entelechy Leibniz was upholding the soul of [14] scholastic doctrine, while retrenching the limbs and outward flourishes. The doctrine of substantial form which he learnt in his youth had had _something_ in it; he could not settle down in the principles of Descartes or of Gassendi, because both ignored this vital _something_. Since the requirements of a new science would not allow a return to sheer scholasticism, it was necessary to find a fresh philosophy, in which entelechy and mechanism might be accommodated side by side. If one had asked any 'modern' of the seventeenth century to name the 'ancient' doctrine he most abominated, he would most likely have replied, 'Substantial form'. Let us recall what was rejected under this name, and why.