In fulfilment of the design thus announced, he tells us, in his "own life," "In 1751, I removed from the country to the town, the true scene for a man of letters." We find, from the dating of his letters, that Hume's residence in Edinburgh was for a year or two in "Riddell's Land," and that it was afterwards in "Jack's Land." Since the plan of numbering the houses in each street extended to the Scottish capital, these names have no longer been in general use; but I find that the former applied to an edifice in the Lawnmarket, near the head of the West Bow, and that the latter was a tenement in the Canongate, right opposite to a house in which Smollet occasionally resided with his sister. The term "Land" applied to one of those edifices--some of them ten or twelve stories high,--in which the citizens of Edinburgh, pressed upwards as it were by the increase of the population within a narrow circuit of walls, made stair-cases supply the place of streets, and erected perpendicular thoroughfares. A single floor of one of these edifices was, a century ago, sufficient to accommodate the family of a Scottish nobleman; and we may be certain, that a very small "Flat" would suit the economical establishment of Hume. In 1751, appeared the "Inquiry concerning the Principles of Morals,"[344:1] the full development, so far as it was made by Hume, of the utilitarian system. The leading principle kept in view throughout this work, is, that its tendency to be useful to mankind at large, is the proper criterion of the propriety of any action, or the justness of any ethical opinion. In this spirit he examines many of the social virtues, and shows that it is their usefulness to mankind that gives them a claim to sympathy, and a title to be included in the list of virtues. The defects of this exposition of the utilitarian system, are marked by the manner in which it was critically attacked. In 1753 a controversial examination of it was made, with temper and ability, by James Balfour of Pilrig,[344:2] who in 1754 succeeded to the chair, in the university of Edinburgh, which Hume had been desirous of filling.[345:1] Mr. Balfour's great argument is the universality of the admission by mankind, in some shape or other, of the leading cardinal virtues, and the unhesitating adoption and practice of them by men on whom the utilitarian theory never dawned, and who are unconscious that their isolated acts are the fulfilment of any general or uniform law. Mr. Balfour argued that we must thus look to something else than utility, as the criterion of moral right and wrong. But a supporter of the utilitarian system, as it has been more fully developed in later days, would probably only take from Mr. Balfour's argument a hint to enlarge the scope of Hume's investigations. To the inquiry, how far utility is the proper end of human conduct, he would add the inquiry, how far the theory has been practically adopted by mankind at large.