reasons from _assumed_ premises--from premises which might be totally without foundation in fact, and which are not pretended to be universally in accordance with it. The conclusions of Political Economy, consequently, like those of geometry, are only true, as the common phrase is, _in the abstract_; that is, they are only true under certain suppositions, in which none but general causes--causes common to the _whole class_ of cases under consideration--are taken into the account. This ought not to be denied by the political economist. If he deny it, then, and then only, he places himself in the wrong. The _à 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.