His definition of wealth, for instance, is not sufficiently accurate; nor does he adhere to it with sufficient uniformity: yet it cannot be doubted that he means by the term generally the material products which are necessary, useful, and agreeable to man, and are not furnished by nature in unlimited abundance; and I own I feel quite convinced that it is in this sense in which it is most generally understood in society, and in which it may be most usefully applied, in explaining the causes of the wealth of nations. In adopting the labour which a commodity will command as the measure of its value, he has not, as it appears to me, given the most conclusive reasons for it, nor has he in all cases made it quite clear whether he means the labour which a commodity will command, or the labour worked up in it. He has more frequently failed in not adhering practically to the measure he had proposed, and in substituting as an equivalent the quantity of corn a commodity will command, which, as a measure of value, has properties essentially distinct from labour. Yet, with all this, it must be acknowledged that he has generally used the terms labour and value in the sense in which they are ordinarily understood in society, and has, with few exceptions, applied labour as the measure of value in the way in which it may be made most extensively useful in the explanation of the science. It has been sometimes objected to Adam Smith, that he has applied the term _productive_ in a new and not very appropriate sense. But if we examine the manner in which this term is applied in ordinary conversation and writing, it must be allowed that, whatever meaning may be thought to attach to it, from its derivation, it is practically used as implying causation in regard to almost any effect whatever. Thus we say that such and such things are productive of the best effects, others of the very worst effects, and others are unproductive of, or do not produce, any perceptible effects; meaning by these expressions, that some things cause the best effects, others the worst effects, others, again, cause no perceptible effects; and these effects may, of course, apply according to the context, and the subject under discussion, to the health of the body, the improvement of the mind, the structure of society, or the wealth of a nation.