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by requiring more labor for their production; manufactures, from the changes in machinery, which are always progressive and never retrograde, are constantly tending to grow cheaper by requiring less; consequently, there is nothing which, upon Mr. Ricardo’s theory, can long continue stationary in value. If, therefore, he had proposed any measure of value, he must have forgotten his own principle of value.

Phil
. But allow me to ask; if that principle is not proposed as a measure of value, in what character is it proposed?

X
. Surely, Philebus, as the ground of value; whereas a measure of value is no more than a criterion or test of value. The last is simply a principium cognoscendi, whereas the other is a principium essendi.

Phil
. But wherein lies the difference?

X
. Is it possible that you can ask such a question? A thermometer measures the temperature of the air; that is, it furnishes a criterion for ascertaining its varying degrees of heat; but you cannot even imagine that a thermometer furnishes any ground of this heat. I wish to know whether a day’s labor at the time of the English Revolution bore the same value as a hundred years after at the time of the French Revolution; and, if not the same value, whether a higher or a lower. For this purpose, if I believe that there is any commodity which is immutable in value, I shall naturally compare a day’s labor with that commodity at each period. Some, for instance, have imagined that corn is of invariable value; and, supposing one to adopt so false a notion, we should merely have to inquire what quantity of corn a day’s labor would exchange for at each period, and we should then have determined the relations of value between labor at the two periods. In this case, I should have used corn as the measure of the value of labor; but I could not rationally mean to say that corn was the ground of the value of labor; and, if I said that I made use of corn to determine the value of labor, I should employ the word “determine” in the same sense as when I say that the thermometer determines the heat–namely, that it ascertains it, or determines it to my knowledge (as a principium cognoscendi). But, when Mr. Ricardo says that the quantity of labor employed on A determines the value of A, he must of course be understood to mean that it causes A to be of this value, that it is the ground of its value, the principium essendi of its value; just as when, being asked what determines a stone to fall downwards rather than upwards, I answer that it is the earth’s attraction, or the principle of gravitation, meaning that this principle causes it to fall downwards; and if, in this case, I say that gravitation “determines” its course downwards, I no longer use that word in the sense of ascertain; I do not mean that gravitation ascertains it to have descended; but that gravitation has causatively impressed that direction on its course; in other words, I make gravitation the principium essendi of its descent.

Phed
. I understand your distinction; and in which sense do you say that Mr. Malthus has used the term Measure of Value–in the sense of a ground, or of a criterion?

X
. In both senses; he talks of it as “accounting for” the value of A, in which case it means a ground of value; and as “estimating” the value of A, in which case it means a criterion of value. I mention these expressions as instances; but, the truth is, that, throughout his essay entitled “The Measure of Value Stated and Illustrated” and throughout his “Political Economy” (but especially in the second chapter, entitled “The Nature and Measures of Value”), he uniformly confounds the two ideas of a ground and a criterion of value under a much greater variety of expressions than I have time to enumerate.