The theory of substantial or accidental forms did more than to lead to nonsense like the above; it introduced errors which stood in the way of any clear investigation of real causes. For example, since some bodies fell toward the earth while others rose in the air, it was said that gravity was the substantial form of the former and lightness of the latter. Thus heavy and light bodies were distinguished as two classes of bodies having properties essentially different, and they were kept from the inquiry whether these apparently different phenomena did not have an identical cause and could not be explained by the same law. It was thus again that seeing water rise in an empty tube, instead of inquiring under what more general fact this phenomena could be subserved, they imagined a virtue, an occult quality, a hatred on the part of the vacuum, and this not only concealed the ignorance under a word void of sense but it made science impossible because a metaphor was taken for an explanation.
So great had become the abuse of the substantial forms, the occult qualities, the sympathetic virtues, etc., that it was a true deliverance when Gassendi on the one hand and Descartes on the other founded a new physics on the principle that there is nothing in the body which is not contained in the mere conception of bodies, namely extension. According to these new philosophers all the phenomena of bodies are only modifications of extension and should be explained by the properties inherent in extension, namely, form, position, and motion. Upon this principle nothing happens in bodies of which the understanding is not able to form a clear and distinct idea. Modern physics seems to have partially confirmed this theory, when it explains sound and light by movements (vibrations, undulations, oscillations, etc.), either of air or of ether.
It has often been said that the march of modern science has been in the opposite direction from the Cartesian philosophy, in that the latter conceives of matter as a dead and inert substance while the former represents it as animated by forces, activities and energies of every kind. This it seems to me is to confuse two wholly different points of view, that is the physical and the metaphysical points of view. The fact seems to be that from the physical point of view, science has rather followed the line of Descartes, reducing the number of occult qualities and as far as possible explaining all the phenomena
