Now though, in the more advanced stages of society, the producer is not always at the same time the demander and consumer; yet the effectual demand for commodities must, on an average, be proportioned to the productive services set in motion to obtain them;[89] and when the different kinds of producers are reduced to a common denominator, such as common agricultural day-labour, and profits are deducted as the remuneration of the capitalist, and rent as the remuneration of the landowner, the proportion which the remaining produce bears to the number of such producers must represent, exactly in the same manner as in the early periods of society, the degree of scarcity in which the commodity exists compared with the producers; and therefore the value of the commodity is measured by the quantity of it which will command a day’s common labour. In fact, if it be once allowed that when labour is exclusively concerned, the number of days’ labour necessary to produce a commodity at any place and time represents the natural value of the commodity at that place and time[90], then, as it is quite certain that the value in exchange of any other commodity compared with the first, will be accurately in proportion to the respective quantities of the same kind of labour which they will command, it follows necessarily, that the value of the second commodity must always be in proportion to the quantity of labour it will command, however its value may have been affected by profits, rents, taxes, monopolies, or the accidental state of its supply compared with the demand. Seventhly: It has been stated that the values of commodities must be proportioned to the causes of value operating upon them. The author of the Critical Dissertation has a chapter on the causes of value, and, at the conclusion of it, adverting to the variety of considerations operating upon the human mind, which he thinks have been overlooked by political economists, he observes, “these considerations are the causes of value; and the attempt to proportion the quantities in which commodities are exchanged for each other to the degree in which one of these considerations exists, must be vain and ineffectual. All, in reality, that can be accomplished on this subject, is to ascertain the various causes of value; and, when this is done, we may always infer, from an increase or diminution of any of them, an increase or diminution of the effect.”[91]