d, and not merely of degree.(10) The present history is restricted
accordingly to the treatment of the two latter species of free
thought,--the resistance of the human mind to the Christian religion as
communicated through revelation, either in part or in whole, neither the
scepticism which disintegrates it, or the unbelief which rejects it: the
former directing itself especially against Christianity, the latter
against the idea of revelation, or even of the supernatural generally.

An analogous reason to that which excludes the history of Protestantism,
excludes also that of the opposition made to Christianity by heresy, and
by rival religions:(11) inasmuch as they repose on authorities, however
false, and do not profess to resort to an unassisted study of nature and
truth.

This account of the province included under free thought will prepare the
way for the explanation of the mode in which the subject is treated.

It is clear that the history, in order to rise above a chronicle, must
inquire into the causes which have made freedom of inquiry develop into
unbelief. The causes have usually been regarded by theologians to be of
two kinds, viz. either superhuman or human; and, if of the latter kind, to
be either moral or intellectual. Bishop Van Mildert, in his History of
Infidelity, restricted himself entirely to the former.(12) Holding
strongly that the existence of evil in the world was attributable, not
only indirectly and originally, but directly and perpetually, to the
operation of the evil spirit, he regarded every form of heresy and
unbelief to be the attempt of an invisible evil agent to thwart the truth
of God; and viewed the history of infidelity as the study of the results
of the operation of this cause in destroying the kingdom of righteousness.
Such a view invests human life and history with a very solemn character,
and is not without practical value; but it will be obvious that an
analysis of this kind must be strictly theological, and removes the
inquiry from the province of human science. Even when completed, it leaves
unexplored the whole field in which such an evil principle operates, and
the agencies which he employs as his instruments.

The majority of writers on unbelief accordingly have treated the subject
from a less elevated point of view, and have limited their inquiry to the
sphere of the operation of human causes, the _media axiomata_ as it
were,(13) which express the motives and agencies wh