believe. His theory of knowledge was that of Locke and Condillac, and
on this foundation he built up his system of scientific naturalism
and dogmatic atheism.

His initial assumption is, as has been suggested, that experience
(application reiteree des sens) and reason are trustworthy guides
to knowledge. By them we become conscious of an external objective
world, of which sentient beings themselves are a part, from which
they receive impressions through their sense organs. These myriad
impressions when compared and reflected upon form reasoned knowledge
or truth, provided they are substantiated by repeated experiences
carefully made. That is, an idea is said to be true when it conforms
perfectly with the actual external object. This is possible unless
one's senses are defective, or one's judgment vitiated by emotion
and passion.

Holbach's contention is that if one applies experience and reason
to the external universe, or nature, "ce vaste assemblage de tout
ce qui existe"; it reveals a _single objective reality_, i. e.,
_matter_, which is in itself essentially active or in a state of motion.

From matter in motion are derived all the phenomena that strike our
senses. All is matter or a function of it. Matter, then, is not
an effect, but a cause. It is not caused; it is from eternity and
of necessity. The cardinal point in Holbach's philosophy is an
inexorable materialistic necessity. Nothing, then, is exempt from
the laws of physics and chemistry. Inorganic substance and organic
life fall into the same category. Man himself with all his differentiated
faculties is but a function of matter and motion in extraordinary
complex and involved relations. Man's imputation to himself of free