You ask of us an effort equal to two, in order to furnish ourselves with articles only attainable at home by an effort equal to four.

You can do it because with you Nature does half the work.

But we will have nothing to do with it; we will wait till your climate, becoming more inclement, forces you to ask of us a labor equal to four, and then we can treat with you _upon an equal footing_." A is a favored country; B is maltreated by Nature.

Mutual traffic then is advantageous to both, but principally to B, because the exchange is not between _utility_ and _utility_, but between _value_ and _value_.
Now A furnishes a greater _utility in a similar value_, because the _utility_ of any article includes at once what Nature and what labor have done; whereas the _value_ of it only corresponds to the portion accomplished by labor.

B then makes an entirely advantageous bargain; for by simply paying the producer from A for his labor, it receives in return not only the results of that labor, but in addition there is thrown in whatever may have accrued from the superior bounty of Nature.
We will lay down the general rule.
Traffic is an exchange of _values_; and as value is reduced by competition to the simple representation of labor, traffic is the exchange of equal labors.