"The word value has two different meanings and sometimes expresses the usefulness of a specific object and other times the ability to purchase other goods that the possession of this object allows. The first could be called "use value" and the second "exchange value". Things that have the greatest use value often have little or no exchange value. Nothing is more useful than water: but with it we can buy very few things, with very few things we can exchange it. On the other hand, a diamond has minimal use value, but we can easily exchange it for a large quantity of other goods.
In order to explore the principles that regulate the exchangeable value of goods, we will try to show:
First, what is the real measure of this exchangeable value, or what constitutes the real price of all goods.
Second, what are the various parts that make up this real price.
And finally, what are the real circumstances that sometimes increase certain parts or the whole of the above parts of the price and sometimes compress them below their natural or normal level. Or, what are the causes that sometimes prevent the coincidence of the market price, that is, the real price of goods, with what we could call their natural price". (Adam Smith)