greater number of persons, particularly during the last twenty or thirty years. All the main propositions of the science have been examined, and the events which have since occurred, tending either to illustrate or confute them, have been repeatedly discussed. The result of this examination and discussion seems to be, that on some very important points there are still great differences of opinion. Among these, perhaps, may be reckoned—The definitions of wealth and of productive labour—The nature and measures of value—The nature and extent of the principles of demand and supply—The origin and progress of rent—The causes which determine the wages of labour and the profits of stock—The causes which practically retard and limit the progress of wealth—The level of the precious metals in different countries—The principles of taxation, &c. On all these points, and many others among the numerous subjects which belong to political economy, differences have prevailed among persons whose opinions are entitled to attention. Some of these questions are to a certain degree theoretical; and the solution of them, though obviously necessary to the improvement of the science, might not essentially affect its practical rules; but others are of such a nature, that the determination of them one way or the other will necessarily influence the conduct both of individuals and of governments; and their correct determination therefore must be a matter of the highest practical importance.
In a science such as that of political economy, it is not to be expected that an universal assent should be obtained to all its important propositions; but, in order to give them their proper weight and justify their being acted upon, it is extremely desirable, indeed almost necessary, that a considerable majority of those who, from their attention to the subject, are considered by the public as likely to be the most competent judges, should agree in the truth of them.
Among those writers who have treated the subject
