To cause this, it is only necessary that less human labor should be required to furnish it.
When the water-carrier comes to supply my house, were I to pay him in proportion to the _absolute utility_ of the water, my whole fortune would not be sufficient.

But I pay him only for the trouble he has taken.

If he requires more, I can get others to furnish it, or finally go and get it myself.

The water itself is not the subject of our bargain; but the labor taken to get the water.

This point of view is so important, and the consequences that I am going to draw from it so clear, as regards the freedom of international exchanges, that I will still elucidate my idea by a few more examples.
The alimentary substance contained in potatoes does not cost us very dear, because a great deal of it is attainable with little work.