PREFACE. with that minuteness and closeness of attention which are due to its importance. Writers on political economy have generally contented themselves with a short definition of the term value, and a distinction of the property de- noted by it into several kinds, and have then proceeded to employ the word with various degrees of laxity. Not one of them has brought into distinct view and discussion the nature of the idea represented by this term, or the inferences which a full perception of its meaning immediately suggests; and the neg- lect of this preliminary labour has created dif. ferences of opinion and perplexities of thought, which otherwise could never have existed. There has been still more laxity, both of thought and expression, regarding the mea- surement of value. The vague manner in which the word measure, necessarily of fre quent occurrence in the pages of the political