The maxims by which it was sought to constitute _a priori_ a scheme of natural laws could not justly claim descent from the necessities of Thought. Had the Schoolmen formed a true conception of the nature of Knowledge they would never have imagined that any necessity of Thought obliged them to believe that a 10 lb. weight would fall to the ground more rapidly than a 1 lb. weight. Equally true is it that their scientific principles had not been derived from any study of the action of natural law. They were unacknowledged intellectual orphans. The movement associated with the names of Galileo, Bruno, Bacon, Kepler, and Newton owed its origin and its success to the abandonment of this vicious principle. So far as Nature was concerned, the Mind was regarded as a _tabula rasa_, and the physician set himself to ascertain the laws of nature not by reflection upon his own mental processes or requirements, but by experiment with and observation of natural processes themselves. The result has been the establishment of modern science--the greatest triumph which the human mind has yet achieved. In a criticism of the writer's essay on _The Dynamic Foundation of Knowledge_ in the _Revue neo-scolastique_ of Louvain, the critic wrote as follows: "Remarquons qu'il n'a pas compris la synthèse scolastique du moyen âge, elle qui cependant a concilié d'une façon admirable l'_actuel_ et le _potentiel_ dans l'explication de la nature des choses. Il s'est mepris aussi sur les caractères de la méthode scolastique de connaître la constitution intime du monde experimental; il croît cette méthode exclusivement deductive." We have felt that candour demanded that we should quote the foregoing passage--coming as it does from a source exceptionally well qualified to express an opinion. If we have nevertheless allowed ourselves in the precedent paragraphs of this essay to express again the view which this critic seeks to qualify, but which we still think in the main sound, we are at the same time very glad to be able in this way to invite attention to the undoubted fact that the distinction between the actual and the potential was recognised by the schoolmen as of a very deep significance. We believe further that the real secret of the failure of mediævalism to extend its Knowledge of Nature was not so much a preference for deductive over inductive methods as the failure to realise that Nature was a dynamic operation. It is important, then, to understand accurately what is the method of Science.