, as shall induce us to look for them in the right
quarter. But such is the nature of the human understanding, that the
very fact of attending with intensity to one part of a thing, has a
tendency to withdraw the attention from the other parts. We are
consequently in great danger of adverting to a portion only of the
causes which are actually at work. And if we are in this predicament,
the more accurate our deductions and the more certain our conclusions in
the abstract, (that is, making abstraction of all circumstances except
those which form part of the hypothesis,) the less we are likely to
suspect that we are in error: for no one can have looked closely into
the sources of fallacious thinking without being deeply conscious that
the coherence, and neat concatenation of our philosophical systems, is
more apt than we are commonly aware to pass with us as evidence of their
truth.

We cannot, therefore, too carefully endeavour to verify our theory, by
comparing, in the particular cases to which we have access, the results
which it would have led us to predict, with the most trustworthy
accounts we can obtain of those which have been actually realized. The
discrepancy between our anticipations and the actual fact is often the
only circumstance which would have drawn our attention to some important
disturbing cause which we had overlooked. Nay, it often discloses to us
errors in thought, still more serious than the omission of what can with
any propriety be termed a disturbing cause. It often reveals to us that
the basis itself of our whole argument is insufficient; that the data,
from which we had reasoned, comprise only a part, and not always the
most important part, of the circumstances by which the result is really
determined. Such oversights are committed by very good reasoners, and
even by a still rarer class, that of good observers. It is a kind of
error to which those are peculiarly liable whose views are the largest
and most philosophical: for exactly in that ratio are their minds more
accustomed to dwell upon those laws, qualities, and tendencies, which
are common to large classes of cases, and which belong to all place and
all time; while it often happens that circumstances almost peculiar to
the particular case or era have a far greater share in governing that
one case.

Although, therefore, a philosopher be convinced that no general truths
can be attained in the affairs of nations by the _a posteriori_ road,