power of purchasing other goods which the possession of that object conveys.
The one may be called ' value in use ;' the other, 'value in exchange.' The
things which have the greatest value in use have frequently little or no
value in exchange ; and, on the contrary, those which have the greatest
value in exchange have frequently little or no value in use. Nothing is more
useful than water ; but it will purchase scarce any thing; scarce any thing
can be had in exchange for it. A diamond, on the contrary, has scarce any
value in use; but a very great quantity of other goods may frequently be had
in exchange for it.

In order to investigate the principles which regulate the exchangeable value
of commodities, I shall endeavour to shew,

First, what is the real measure of this exchangeable value; or wherein
consists the real price of all commodities.

Secondly, what are the different parts of which this real price is composed
or made up.

And, lastly, what are the different circumstances which sometimes raise some
or all of these different parts of price above, and sometimes sink them
below, their natural or ordinary rate; or, what are the causes which
sometimes hinder the market price, that is, the actual price of commodities,
from coinciding exactly with what may be called their natural price.

I shall endeavour to explain, as fully and distinctly as I can, those three
subjects in the three following chapters, for which I must very earnestly
entreat both the patience and attention of the reader : his patience, in
order to examine a detail which may, perhaps, in some places, appear
unnecessarily tedious; and his attention, in order to understand what may