Adam Smith. An inquiry into the nature and causes of the wealth of Nations (№ 347131)

It should be noted that the word value has two different meanings: sometimes it refers to the usefulness of any object, and sometimes the opportunity to purchase other items that comes from the subject. The first can be called use-value, the second is exchange value. Items with very high use value often have very little exchange value or even do not have one; the objects has a very high exchange value often have a very small use or do not have. There is nothing more useful than water, but it is almost nothing to buy to receive in exchange for it. On the contrary, the diamond almost has no use value, but often in exchange it is possible to obtain a very large number of other goods.