hen, and then only, he places himself in the wrong. The _a priori_
method which is laid to his charge, as if his employment of it proved
his whole science to be worthless, is, as we shall presently show, the
only method by which truth can possibly be attained in any department of
the social science. All that is requisite is, that he be on his guard
not to ascribe to conclusions which are grounded upon an hypothesis a
different kind of certainty from that which really belongs to them. They
would be true without qualification, only in a case which is purely
imaginary. In proportion as the actual facts recede from the hypothesis,
he must allow a corresponding deviation from the strict letter of his
conclusion; otherwise it will be true only of things such as he has
arbitrarily supposed, not of such things as really exist. That which is
true in the abstract, is always true in the concrete with proper
_allowances_. When a certain cause really exists, and if left to itself
would infallibly produce a certain effect, that same effect, _modified_
by all the other concurrent causes, will correctly correspond to the
result really produced.

The conclusions of geometry are not strictly true of such lines, angles,
and figures, as human hands can construct. But no one, therefore,
contends that the conclusions of geometry are of no utility, or that it
would be better to shut up Euclid's Elements, and content ourselves with
"practice" and "experience."

No mathematician ever thought that his definition of a line corresponded
to an actual line. As little did any political economist ever imagine
that real men had no object of desire but wealth, or none which would
not give way to the slightest motive of a pecuniary kind. But they were
justified in assuming this, for the purposes of their argument; because
they had to do only with those parts of human conduct which have
pecuniary advantage for their direct and principal object; and because,
as no two individual cases are exactly alike, no _general_ maxims could
ever be laid down unless _some_ of the circumstances of the particular
case were left out of consideration.

But we go farther than to affirm that the method _a priori_ is a
legitimate mode of philosophical investigation in the moral sciences: we
contend that it is the only mode. We affirm that the method _a
posteriori_, or that of specific experience, is altogether inefficacious
in those sciences, as a means of arriving at any c