of readers, or liable to be misunderstood.”[469] If any word must have a different meaning from that adopted by either of these authorities, the new sense must not only be free from the faults of the old, but must have a clear and recognizable positive usefulness. The new definitions should be consistent with the old; and the same terms should be used in the same sense, except where inveterate custom insists on an exception. When all is done, it is still impossible in a social science like political economy to find a definition entirely beyond cavil.[470] “Wealth” must include all the “material objects that are necessary, useful, or agreeable to mankind;”[471] “productive labour” must be the labour which realizes itself either in such material objects or the increased value of them; or else we wander from common language, and our discussions travel off into indefiniteness. Economical reasoning must be a deduction from observed facts of nature and of human nature verified by general experience. Malthus professes to have used this cautious method throughout, and the theory of population was only the particular instance where circumstances enabled him to make his verification most complete. “I should never have had that steady and unshaken confidence in the theory of population which I have invariably felt, if it had not appeared to me to be confirmed, in the most remarkable manner, by the state of society as it actually exists in every country with which we are acquainted.”[472] On the other hand, Ricardo, legislating for Saturn, gives us little or no verification by experience. It is true that he admits qualifications and exceptions to his own statements; and he would have winced a little at his own biographer’s assertion that “Mr. Ricardo paid comparatively little attention to the practical application of general principles; his is not a practical work.”[473] But he makes no use of the admissions; his illustrations as a rule are not historical, but imaginary cases and the verification is wanting. In a letter to Malthus (written on the 24th November, 1820) he says: “Our differences may in some respects, I think, be ascribed to your considering my book as more practical than I intended it to be. My object was to elucidate principles, and to do this I imagined strong cases, that I might show the operation of these principles.”[474] In Malthus and Adam Smith, imaginary cases are rare exceptions, actual examples from life or history are the rule. Malthus goes so far in this direction that (to use his own phraseology) he is tempted to subordinate science to “utility.” Even Adam Smith, though he had abundance of good-will to his kind, did not write to do good but to expound truth. To Malthus the discovery of truth was less important than the improvement of society. When an economical truth could not be made the means of improvement, he seems to have lost interest in it. His pointed warning