Cartesianism affirmed the two positive axioms of the supremacy of reason, and the invariability of the laws of nature; and its instrument was a new rigorous analytical method, which was applicable to history as well as to physical knowledge.  The axioms had destructive corollaries.  The immutability of the processes of nature collided with the theory of an active Providence.  The supremacy of reason shook the thrones from which authority and tradition had tyrannised over the brains of men.  Cartesianism was equivalent to a declaration of the Independence of Man.

It was in the atmosphere of the Cartesian spirit that a theory of Progress was to take shape.

1.

Let us look back.  We saw that all the remarks of philosophers prior to the seventeenth century, which have been claimed as enunciations of the idea of Progress, amount merely to recognitions of the obvious fact that in the course of the past history of men there have been advances and improvements in knowledge and arts, or that we may look for some improvements in the future.  There is not one of them that adumbrates a theory that can be called a theory of Progress.  We have seen several reasons why the idea could not emerge in the ancient or in the Middle Ages.  Nor could it have easily appeared in the period of the Renaissance.  Certain preliminary conditions were required, and these were not fulfilled till the seventeenth century.  So long as men believed that the Greeks and Romans had attained, in the best days of their civilisation, to an intellectual plane which posterity could never hope to reach, so long as the authority of their thinkers was set up as unimpeachable, a theory of degeneration held the field, which excluded a theory of Progress.  It was the work of Bacon and Descartes to liberate science and philosophy from the yoke of that authority; and at the same time, as we shall see, the rebellion began to spread to other fields.

Another condition for the organisation of a theory of Progress was a frank recognition of the value of mundane life and the subservience of knowledge to human needs.  The secular spirit of the Renaissance prepared the world for this new valuation, which was formulated by Bacon, and has developed into modern utilitarianism.

There was yet a third preliminary condition.  There can be no certainty that knowledge will continually progress until science has been placed on sure foundations.  And science does not rest for us on sure foundations unless the invariability of the laws of nature is admitted.  If we do not accept this hypothesis, if we consider it possible that the uniformities of the natural world may be changed from time to time, we have no guarantee that science can progress indefinitely.  The philosophy of Descartes established this principle, which is the palladium of science; and thus the third preliminary condition was fulfilled.

2.