But while the philosopher and the practical man bandy half-truths with one another, we may seek far without finding one who, placed on a higher eminence of thought, comprehends as a whole what they see only in separate parts; who can make the anticipations of the philosopher guide the observation of the practical man, and the specific experience of the practical man warn the philosopher where something is to be added to his theory. The most memorable example in modern times of a man who united the spirit of philosophy with the pursuits of active life, and kept wholly clear from the partialities and prejudices both of the student and of the practical statesman, was Turgot; the wonder not only of his age, but of history, for his astonishing combination of the most opposite, and, judging from common experience, almost incompatible excellences. Though it is impossible to furnish any test by which a speculative thinker, either in Political Economy or in any other branch of social philosophy, may know that he is competent to judge of the application of his principles to the existing condition of his own or any other country, indications may be suggested by the absence of which he may well and surely know that he is not competent. His knowledge must at least enable him to explain and account for what _is_, or he is an insufficient judge of what ought to be. If a political economist, for instance, finds himself puzzled by any recent or present commercial phenomena; if there is any mystery to him in the late or present state of the productive industry of the country, which his knowledge of principle does not enable him to unriddle; he may be sure that something is wanting to render his system of opinions a safe guide in existing circumstances. Either some of the facts which influence the situation of the country and the course of events are not known to him; or, knowing them, he knows not what ought to be their effects. In the latter case his system is imperfect even as an abstract system; it does not enable him to trace correctly all the consequences even of assumed premises. Though he succeed in throwing doubts upon the reality of some of the phenomena which he is required to explain, his task is not yet completed; even then he is called upon to show how the belief, which he deems unfounded, arose; and what is the real nature of the appearances which gave a colour of probability to allegations which examination proves to be untrue.