_ 323 Bacon_ had already said of the nobility, clergy and literateurs: _sorti reipublicæ nihil addunt_ (Serm., 15, 29); in opposition to which, _Hobbes_ justly remarks, that even human labor may, like other things, be exchanged against goods of all sorts. (Leviathan, 24.) In the work, Discourse of Trade, Coyn and Credit, p. 44 ff., and p. 156, the absolute necessity of “head-work” as well as bodily labor, is conceded; but it is insisted that physicians, clergymen and jurists can never enrich a country, and that a relatively large number of them would even conduce to national poverty. (See _Roscher_, Geschichte der englischen Volkswirthschaftslehre, 138.) _David Hume_ considers merchants as productive, but says that a doctor or lawyer can grow rich only at the expense of some one else. (Discourses, No. 4, On Interest.) _Ferguson_ very cleverly compares such a valuation of national wealth to that of a miser. Hist. of Civil Society, VI, I. 324 Similarly _Lauderdale_, Inquiry, 355; _Lotz_, Handbuch der Staätswirthschaft, I, § 39, and _Rau_, Lehrbuch I, § 195, concede only indirect productiveness to commerce. It may be shown, in a great many instances, that such productiveness exists side by side with direct productiveness, on account of the thousand ways in which all economic threads are interwoven with one another. Thus _Paley_ remarks in his work on the Principles of Morals and Politics, that a tobacco manufacturer even may contribute indirectly to the cultivation of grain; an actor, to industry etc.