In this work of model clarity, Yves Simon discusses the basic insights of the creators of modern thought: Descartes, Newton, Galileo, Comte, Mach, Meyerson, Bergson, Planck, and the issues at stake in the development of modern science and in the rejection of the Aristotelian physics. Simon distinguishes between a philosophy of nature and a science of nature - and grants a real value to both. A discussion of this vexing problem and its application to the modern controversy over determinism and chance raised by modern physics rounds out this philosophical and historical highlighting of man's most important theories of nature.