It might be allowed, perhaps, that labour would be a still more satisfactory measure of value, in all countries and at all times, if the physical force exerted in a day’s labour were always the same; and probably this is sometimes not far from being the case in a few countries as compared with each other, and more frequently in the same country at different periods. The English agricultural labourers in the time of Edward III., though probably less skilful, worked, I should conceive, for nearly the same number of hours, and exerted nearly the same physical force, as our labourers at present. Under such circumstances, and in the same country, agricultural labour seems to be a measure of value from century to century calculated to satisfy the scruples of the most fastidious. But even when it is acknowledged, that the labourer at different times and in different countries does _not_ always lay down the same portion of his ease, his liberty, and happiness, the quality of labour, as a measure of value, is not essentially impaired; and it appears to me always true, that when commodities in different countries and at different times have been found to command the same quantity of the agricultural labour of each country and time, they may with propriety be said to have been held in the same estimation, and considered as of the same value. We may now proceed to the definition of some of the most important terms in common use among political economists, particularly those which have been most controverted. Whenever it has been thought necessary either to deviate from the general rule of employing terms according to their ordinary meaning, or to determine between two meanings both of which have some authorities in their favour, I have always been guided in my choice by what appeared to me the superior practical utility of the meaning selected in explaining the causes of the wealth of nations.[95]