437. Empiric Naturalism. Telesius. -- BERNARDINUS TELESIUS (1508-1588), the founder of Renaissance naturalism, devoted himself entirely to the study of the natural sciences, coupled with an acrimonious and lifelong campaign against the physics of the Aristotelians. He founded the Accademia Telesiana at Naples for the promotion of the natural sciences. His principal treatise, De Natura Rerum juxta Propria Principia, is the frank, yet logical, effort of a physicist pure and simple, to explain Universal Nature by the interplay of a limited number of physical forces.

Within the passive and inert mass of matter that constitutes the universe, God has created two active principles, heat and cold, the principle of movement and the principle of absolute rest. Those two forces, incorporeal and mutually exclusive, share between them the total quantum of created matter. Hence the great division of the created universe into the heavens which are the centre of heat, and the earth which is the centre of cold. Since each principle is endowed with a tendency to self-preservation, each possesses the faculty of feeling the destructive action of its opposite. This overthrows the Aristotelian theory of the four elements (295) and sets up the phenomenon of sensation as a cosmic fact. The individual things that people the earth arise from the contact of the radiant heat of the heavens with the icy surface of the earth: and the same law presides over the formation of minerals and the genesis of living things.

On those principles of physics, Telesius rears a new sort of vitalism which is interesting in its broad lines. The principle of animal life is a spiritus, a modicum of heat, circulating through the body and presiding over all its organic functions. This theory of animal spirits was evidently a revival of the ancient doctrine of the pneuma, and became itself in turn the starting-point of the physiology both of Bacon and of Descartes. The spiritus is not, as in the scholastic system, an emanation from the formative principle (303, n. 1); it takes the place of the substantial form itself: Telesius directed a violent criticism against the Aristotelian theory of hylemorphism. Sensation and appetite are merely modes of action of the spiritus; cognitive phenomena are reduced to transformations of sensation; moral phenomena are traced to the instinct of self-preservation. The human spiritus is more refined and subtle than that of the brute, but does not differ in nature from the latter.

It is true that Telesius corrects this excessive naturalism, like Cardanus and Paracelsus, by admitting the existence in man of a forma superaddita, immaterial and immortal, which enables man to know God (303); but about this form he is concerned only in a very secondary way: he admits it merely to save appearances, and it introduces into his psychology a dualism similar to that with which St. Thomas taxed the partisans of plurality of forms.