At a later stage of this work it will be our duty to call attention to the enthusiasm aroused by this old theory of an _impôt unique_ as advocated in the works of an eminent American economist,[110] who renders homage to the Physiocrats for inspiring him with ideals altogether opposed to those of the landed proprietors. And a similar movement under the very same name—the single-tax system—is still vigorous in the United States. IV: _RÉSUMÉ_ OF THE PHYSIOCRATIC DOCTRINE. CRITICS AND DISSENTERS A brief _résumé_ of the contributions made to economic science by the Physiocrats will help us to realise their great importance. From the theoretical point of view we have: 1. The idea that every social phenomenon is subject to law, and that the object of scientific study is to discover such laws. 2. The idea that personal interest if left to itself will discover what is most advantageous for it, and that what is best for the individual is also best for everybody. But this liberal doctrine had many advocates before the Physiocrats. 3. The conception of free competition, resulting in the establishment of the _bon prix_, which is the most advantageous price for both parties, and implies the extinction of all usurious profit. 4. An imperfect but yet searching analysis of production, and of the various divisions of capital. An excellent classification of incomes and of the laws of their distribution. 5. A collection of arguments which have long since become classic in favour of landed property. From a practical point of view we have: 1. The freedom of labour. 2. Free trade within a country, and an impassionate appeal for the freedom of foreign trade. 3. Limitation of the functions of the State. 4. A first-class demonstration of the superiority of direct taxation over indirect. It is unjust to reproach the Physiocrats, as is sometimes done, with giving us nothing but social metaphysics. A little over-systemisation may prove useful in the early stages of a science. Its very faults have some usefulness. We must admit, however, that although their conception of the “natural order” supplied the foundation, or at least the scaffolding, for political economy, it became so intertwined with a kind of optimism that it nullified the work of the Liberal school, especially in France.[111]