Plato and Aristotle may be taken as typical of the two principal intellectual tendencies which have characterised all subsequent speculation—the Platonist, he who finds in the constitution of the Mind the eternal principles or at least the types of the eternal principles of Reality; the Aristotelian, he for whom these seem to reside in the object and, in the act of Cognition, are merely impressed upon, transferred to, presented to, or otherwise introduced into or apprehended by the Mind.
The Aristotelian view of Nature as an energetic process failed to impress itself upon his successors. Greek Philosophy soon after Aristotle's death decayed or was deprived of its early vigour, and the doctrine which survived the wreck was essentially derived, however imperfectly, from the Platonic theory.
Throughout the first fifteen hundred years of the Christian era this doctrine undoubtedly dominated the course of speculation—a speculation of which much is now forgotten and almost as much was certainly barren and unfruitful, but of which we would entertain a very mistaken notion if we were to imagine that it was not often pursued with great subtlety and acumen.
One natural result of the fact that such a principle dominated human thought was the prevalence of a belief that the explanation of Nature and natural processes could be derived from the cognitive faculty itself. Our cognition of our immediate surroundings was doubtless continuously corrected by immediate practical tests. But the science of a more extended view of Nature was vitiated by this false principle and in consequence for many centuries our whole Knowledge of Nature remained unprogressive and unfruitful.
Causa æquat effectum, Nature abhors a vacuum, are examples of the maxims derived or supposed to be derived from the necessities of our Reason, and by the aid of which it was vainly hoped to attain a knowledge of Nature and natural laws.
The principle was in itself unsound.
The necessary laws of our rational faculty could discover to us only the essentials of that faculty itself.
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.
