I cannot pretend to advance, as a confirmation of this doctrine, that the establishment of slavery in our colonies in America was made with a view to promote agriculture, and to curb manufactures in the new world, because I do not know much of the sentiments of politicians at that time: but if it be true, that slavery has the effect of advancing agriculture, and other laborious operations which are of a simple nature, and at the same time of discouraging invention and ingenuity; and if the mother-country has occasion for the produce of the first, in order to provide or to employ those who are taken up at home in the prosecution of the latter; then I must conclude, that slavery _has been_ very _luckily_, if not _politically_, established to compass such an end: and therefore, if any colony, where slavery is not common, shall ever begin to rival the industry of the mother-country, a very good way of frustrating the attempt will be, to encourage the introduction of slaves into such colonies without any restrictions, and allow it to work its natural effect. Having given the definition of trade and industry, as relative to my inquiry, I come now to examine their immediate connections, the better to cement the subject of this book, with the principles deduced in the former. In treating of the reciprocal wants of a society, and in shewing how their being supplied by labour and ingenuity naturally tends to increase population on one hand, and agriculture on the other, the better to simplify our ideas, we supposed the transition to be direct from the manufacturer to the consumer, and both to be members of the same society. Matters now become more complex, by the introduction of trade among different nations, which is a method of collecting and distributing the produce of industry, by the interposition of a third principle. Trade receives from a thousand hands, and distributes to as many. To ask, whether trade owes its beginning to industry, or industry to trade, is like asking, whether the motion of the heart is owing to the blood, or the motion of the blood to the heart. Both the one and the other, I suppose, are formed by such insensible degrees, that it is impossible to determine where the motion begins. But so soon as the body comes to be perfectly formed, I have little doubt of the heart’s being the principle of circulation. Let me apply this to the present question. A man must first exist, before he can feel want; he must want, that is, desire, before he will demand; and he must demand, before he can receive. This is a natural chain, and from it we have concluded in Book I. that population is the cause, and agriculture the effect.