And so, in the majority of cases at least, this natural and spontaneous mechanism secures a constant balancing of the quantities of goods produced and the quantities effectively demanded. The circumstances under which such a result does not follow are really quite exceptional—although Smith does not deny that sometimes they do exist. Whenever such conditions obtain—that is, when the market price remains for a considerable length of time above the natural price—we find that it is always due to the capitalists’ action in concealing the high rate of profits which they draw, or in retaining possession of some patent or natural monopoly, such as wine of a special quality. It occasionally happens also as the result of an artificial monopoly.[185] But these are mere exceptions, their rare occurrence confirming the fundamental rule concerning the spontaneous adaptation of the quantity offered to the quantity demanded, thanks to this oscillation of the market price about the natural. This theory of adaptation, we know, is one of the most important in the whole of political economy. Since Smith wrote it has been reproduced by almost every economist, and without any very substantial alteration. It remains even to this day the basis of our theory of production. It is interesting to note the manner in which Smith makes use of his theory to illustrate his thesis. We shall refer to two cases which are intrinsically important as well as affording admirable illustrations of that spontaneity upon which Smith laid such stress.