ich have been
manifested on the theatre of the world, and visible in actual history. It
will be clear that within this sphere the causes are specially of two
kinds; viz. those which have their source in the will, and arise from the
antagonism of feeling, which wishes revelation untrue, and those which
manifest themselves in the intellect, and are exhibited under the form of
difficulties which beset the mind, or doubts which mislead it, in respect
to the evidence on which revelation reposes. The former, it may be feared,
are generally the ground of unbelief; the latter the basis of doubt.
Christian writers, in the wish to refer unbelief to the source of
efficient causation in the human will, with a view of enforcing on the
doubter the moral lesson of responsibility, have generally restricted
themselves to the former of these two classes; and by doing so have
omitted to explore the interesting field of inquiry presented in the
natural history of the variety of forms assumed by scepticism, and their
relation to the general causes which have operated in particular ages:--a
subject most important, if the intellectual antecedents thus discovered be
regarded as causes of doubt; and not less interesting, if, instead of
being causes, they are merely considered to be instruments and conditions
made use of by the emotional powers.

A history of free thought seems to point especially to the study of the
latter class. A biographical history of free thinkers would imply the
former; the investigation of the moral history of the individuals, the
play of their will and feelings and character; but the history of free
thought points to that which has been the product of their characters, the
doctrines which they have taught. Science however no less than piety would
decline entirely to separate the two;(14) piety, because, though admitting
the possibility that a judgment may be formed in the abstract on free
thought, it would feel itself constantly drawn into the inquiry of the
moral responsibility of the freethinker in judging of the concrete
cases;--science, because, even in an intellectual point of view, the
analysis of a work of art is defective if it be studied apart from the
personality of the mental and moral character of the artist who produces
it. If even the inquiry be restricted to the analysis of intellectual
causes, a biographic treatment of the subject, which would allow for the
existence of the emotional, would be requisite.(