Page:A Brief History of Modern Philosophy.djvu/52

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reference to finite things (e.g. matter and the soul); he says however that the concept cannot be used univocally (univoce) of infinite and finite being, because finite beings are always dependent and the term substance is therefore applied to them inexactly. According to the broader, inexact linguistic usage, “Substance” means the same as thing or being, the subject or matter or substrate of given attributes.

2. The idea of God not only guarantees the reality of things, but it is likewise the source of the fundamental principles of natural science. (Principia Philosophiæ, 1644.)

Our sense impressions serve the purpose of guiding us in practical activities. In order to do this they need not be like the things themselves, if only they correspond to them. When we come to think of the real nature of things apart from our sensations, there are only three attributes which are incontrovertible: extension, divisibility and mobility. We cannot even in imagination think these attributes away. And these three attributes furnish the basis of the simplest and clearest understanding of everything that takes place in the material universe, whilst qualities merely furnish illusory explanations. All the attributes of nature may therefore be referred to extension, divisibility and motion. Qualities however are simply to be ascribed to the perceiving subject.—Descartes thus deliberately systematizes the mechanical conception of nature. He seems to have been led to this conclusion by his studies in natural science during the years 1620-1629, independent of Galileo, although perhaps influenced by Kepler.

He derives the first principles of the mechanical conception of nature from the concept of God. As perfect being God must be immutable. The idea of anything