The errors which I have mentioned have been committed principally by those who, without being professedly political economists, frequently indeed expressly disclaiming that character, have treated the subjects which Political Economy considers. But many who have avowedly devoted themselves to its pursuit, seem to have misdirected their efforts, for want of a clear conception of the object of their investigations, of the manner in which they ought to be conducted, or of the nature of the difficulties to be surmounted. If the teacher of Political Economy has not decided whether he is engaged on a science or on an art, whether it is his duty to explain phenomena or to deliver precepts, whether his principal business is to observe facts or to deduce inferences, whether his premises are all physical truths or depend partly on arbitrary assumption,--his work, though it may contain partial views of the highest value, cannot possibly form a clear or a consistent whole. Nor is it sufficient that the professor should have made up his mind as to what he has to teach. It is important, though not equally important, that the student should have a general notion as to what he has to learn, as to the nature of the subjects which are to be laid before him, of the conclusions to which he will be asked to assent, and of the arguments by which they will be supported. The view that is to be taken, may perhaps not suit his habits of thought or of inquiry. It may be too abstract or too concrete. If he be accustomed to demonstration, he may be ill satisfied by proofs and illustrations drawn from actual life, and mixed with irrelevant accidents. If his pursuits have been practical, he may be disgusted by reasonings founded on hypotheses representing nothing that actually takes place. Or his objections may be directed rather against the subject itself than against the mode of its treatment. He may think that too much importance, or if not too much importance, too exclusive an attention, is directed towards wealth. He may wish that economists would consider man as a being with higher qualities, higher duties, and higher enjoyments than those which are concerned in the production, distribution, and consumption of commodities and services, and may regret to see him treated merely as a cause or a recipient of rents, profits, and wages. But if he be forewarned, he will not be disappointed, and, knowing beforehand the sort of study in which he is to be engaged, he will more easily perceive the premises and weigh the arguments of its professor. LECTURE II. POLITICAL ECONOMY A MENTAL STUDY.