by breaking with the past, and using abstract
speculations on original data, but by tracing the growth of thought,
gathering the harvest of past investigations, and learning by experience
to escape error.

These considerations bear upon the present subject in this manner: they
show not only the special adaptation to the passing tastes of the age, of
an historic mode of approaching a subject, but exhibit also that the mode
of proof and of refutation must be sought, not on abstract grounds, but
historic. The position of an enemy is not to be forced, but turned; his
premises to be refuted, not his conclusions; the antecedent reasons which
led him into his opinion to be exhibited, not merely evidence offered of
the fact that he is in error.

This view, that doubt might be refuted by the historic analysis of its
operation, by laying bare the antecedent grounds which had produced it,
will explain why the author was led to believe that a chapter of mental
and moral physiology might be useful, which would not merely carry out the
anatomy of actual forms of disease, but discover their origin by the study
of the preceding natural history of the patients.

These remarks will perhaps suffice for explaining the object which was
proposed in writing this history; and may justify the hope that this work,
thus adapted to the wants of the time, may offer such a contribution to
the subject of the Christian evidences, as not only to possess an
intellectual value, but to coincide with the purpose contemplated by the
founder of the Lectures.

It remains to state the sources which have been used for the literary
materials of the history. Though they are sufficiently indicated in the
notes, a general description of them may be useful.

They may be distributed under four classes;

1. The histories which have been professedly devoted to the subject.

2. The notices of the history of unbelief in general histories of the
church or of literature.

3. (Which ought indeed to rank first in importance;) the original
authorities for the facts, i.e. the works of the sceptical writers
themselves; or of the contemporary authors who have refuted them.

4. The monographs, which treat of particular writers, ages, or schools, of
sceptical thought.

In approaching the subject, a student would probably commence with the
first two classes; and after having thus acquired for himself a _carte du
pays_, would then explore it in detail by the aid of the t