He has done enough when he has proved that such is the fact; and he proves this by showing, on the principles of human nature, that, if it were otherwise, no land except that which is most fertile, and best situated, would be cultivated. All the technical terms, therefore, of Political Economy, represent either purely mental ideas, such as _demand_, _utility_, _value_, and _abstinence_, or objects which, though some of them may be material, are considered by the political economist so far only as they are the results or the causes of certain affections of the human mind, such as _wealth_, _capital_, _rent_, _wages_, and _profits_. In the next Lecture I shall consider the first of the two remaining questions,--namely, whether Political Economy may be better treated as a science or as an art. LECTURE III. REASONS FOR TREATING POLITICAL ECONOMY AS A SCIENCE. In the following Lecture I shall consider whether Political Economy may be better treated as a science or as an art. If Political Economy is to be treated as a science, it may be defined as “the science which states the laws regulating the production and distribution of wealth, so far as they depend on the action of the human mind.” If it be treated as an art, it may be defined as “the art which points out the institutions and habits most conducive to the production and accumulation of wealth.” Or if the teacher venture to take a wider view, as “the art which points out the institutions and habits most conducive to that production, accumulation, and distribution of wealth, which is most favourable to the happiness of mankind.”