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