Every social fact had a place within the “natural order” of the Physiocrats. Such a wide generalisation would have entitled them to be regarded as the founders of sociology rather than of economics. But there was included one purely economic phenomenon which attracted their attention at an early stage, and so completely captivated their imaginations as to lead them on a false quest. This was the predominant position which land occupied as an agent of production—the most erroneous and at the same time the most characteristic doctrine in the whole Physiocratic system. Every productive undertaking of necessity involves certain outgoings—a certain loss. In other words, some amount of wealth is destroyed in the production of new wealth—an amount that ought to be subtracted from the amount of new wealth produced. This difference, measuring as it does the excess of the one over the other, constitutes the net increase of wealth, known since the time of the Physiocrats as the “net product.” The Physiocrats believed that this “net product” was confined to one class of production only, namely, agriculture. Here alone, so it seemed to them, the wealth produced was greater than the wealth consumed. Barring accidents, the labourer reaped more than he consumed, even if we included in his consumption his maintenance throughout a whole year, and not merely during the seasons of harvest and tilth. It was because agricultural production had this unique and marvellous power of yielding a “net product” that economy was possible and civilisation a fact.[27] It was not true of any other class of production, either of commerce or of transport, where it was very evident that man’s labour produced nothing, but merely replaced or transferred the products already produced. Neither was it true of manufacture, where the artisan simply combined or otherwise modified the raw material.[28] It is true that such transfer or accretion of matter may increase the value of the product, but only in proportion to the amount of wealth which had to be consumed in order to produce it; because the price of manual labour is always equal to the cost of the necessaries consumed by the worker. All that we have in this case, however, is a collection of superimposed values with some raw material thrown into the bargain. But, as Mercier de la Rivière put it, “addition is not multiplication.”[29] Consequently, industry was voted sterile. This implied no contempt for industry and commerce. “Far from being useless, these are the arts that supply the luxuries as well as the necessaries of life, and upon these mankind is dependent both for its preservation and for its well-being.”[30] They are unproductive in the sense that they produce no “extra” wealth.