not
merely on our own estimate of the thing, but on everybody else's
estimate; therefore on the number and force of the will of the
concurrent buyers, and on the existing quantity of the thing in
proportion to that number and force.

Hence the price of anything depends on four variables.

(1.) Its cost.

(2.) Its attainable quantity at that cost.

(3.) The number and power of the persons who want it.

(4.) The estimate they have formed of its desirableness.

Its value only affects its price so far as it is contemplated in this
estimate; perhaps, therefore, not at all.

63. Now, in order to show the manner in which price is expressed in
terms of a currency, we must assume these four quantities to be known,
and the "estimate of desirableness," commonly called the Demand, to be
certain. We will take the number of persons at the lowest. Let A and B
be two labourers who "demand," that is to say, have resolved to labour
for, two articles, _a_ and _b_. Their demand for these articles (if the
reader likes better, he may say their need) is to be conceived as
absolute, their existence depending on the getting these two things.
Suppose, for instance, that they are bread and fuel, in a cold country,
and let a represent the least quantity of bread, and _b_ the least
quantity of fuel, which will support a man's life for a day. Let _a_ be
producible by an hour's labour, but _b_ only by two hours' labour.

Then the _cost of a_ is one hour, and of _b_ two (cost, by our
definition, being expressible in terms of time). If, therefore, each man
worked both for his corn and fuel, each would have to work three hours a
day. But they divide the labour for its greater ease.[30] Then if A
works three hours, he produces 3 _a_, which is one a more than both the
men want. And if B works three hours, he produces only 1-1/2 _b_, or
half of _b_ less than both want. But if A work three hours and B six, A
has 3 _a_, and B has 3 _b_, a maintenance in the right proportion for
both for a day and half; so that each might take half a day's rest. But
as B has worked double time, the whole of this day's rest belongs in
equity to him. Therefore the just exchange should be, A giving two _a_
for one _b_, has one _a_ and one _b_;--maintenance for a day. B giving
one _b_ for two _a_, has two _a_ and two _b_; maintenance for two days.

But B cannot rest on the second day, or A would be left without the
article which B produces. Nor is there any means of ma