In the present and the following two Lectures, I shall consider whether Political Economy is a physical or a mental study; whether it may be more conveniently treated as a science or as an art; and whether its premises are to be taken solely from observation and consciousness, or rest, in part, on arbitrary assumptions. And I shall begin by stating, at some length, the distinction between science and art,--not with the hope of saying anything new, but because I believe that that distinction, though it has been clearly drawn, may not be familiar to all my hearers. Shortly, it may be said that, as a history is a statement of past facts, so a science is a statement of existing facts, and an art a statement of the means by which future facts may be caused or influenced, or, in other words, future events brought about. The first two aim only at supplying materials for the memory and the judgment; they do not presuppose any purpose beyond the acquisition of knowledge. The third is intended to influence the will. It presupposes that some object is to be attained, and points out the easiest, the safest, or the most effectual conduct for that purpose. It is for this reason that the collection of related facts which constitute a science is generally a less complex thing than the collection of related precepts which constitute an art. A single science may be complete in itself;--a man may confine himself to chemistry, or to zoology, or to botany. He may pursue any one of those sciences to the boundaries of existing knowledge, and know nothing of the others. But an art must draw its materials from many sciences. No man can teach or practise well the art of agriculture unless he have some knowledge of chemistry, botany, zoology, mechanics, and indeed of many other sciences.