Capital must work, as it were, in concert with industry; and this concurrence is what I call the productive agency of capital. - Jean-Baptiste Say

A science only advances with certainty, when the plan of inquiry and the object of our researches have been clearly defined; otherwise a small number of truths are loosely laid hold of, without their connexion being perceived, and numerous errors, without being enabled to detect their fallacy.

It is, perhaps, a well founded objection to Mr. Ricardo, that he sometimes reasons upon abstract principles to which he gives too great a generalization.

Wherefore it is impossible to succeed in comparing wealth of different eras or different nations. This, in political economy, like squaring the circle in mathematics, is impracticable, for want of a common mean or measure to go by.