Now let us see how the matter stands, when tailor and blacksmith at the same time feel and obey the impulses to a more skilled and vigorous artisan life. Suppose the blacksmith too carries up his efficiency in his own trade to 15, just as the tailor has done, the potency of each in the trick of the other remaining as before at 5; under these circumstances when the two come to trade with each other, each has a relative superiority over the other of 10, and there is an advantage of 20 points to be divided between the two; the trade is now ten times more profitable to each than it was at the outset, when there was only an aggregate of 2 units for the division between two parties; and accordingly the motive to an exchange and the gain of an exchange as between tailor and blacksmith are ten times greater than they were before. Therefore we lay down the principle, as inductively ascertained and as universally applicable to all exchanges, that the greater the relative superiority at different points as between the parties exchanging, the more beneficial and profitable do the exchanges become to all the participators in them. If this principle be just, and we may well flatter ourselves that it will be found to be just, it follows, that every man who has anything to buy or sell, is directly interested in the highest success of his fellow-exchangers, that every trade finds its own advantage in the success of all other trades, and that all discoveries and inventions by which Nature is made to pay tribute to art is, restrictions apart, so much clear gain to the world at large. In the light of sound and broad principles, what David Hume called the "Jealousy of Trade" is simply silly. The mainspring that impels all buyers and sellers to quicken their movements and to improve their methods and thus and otherwise to cheapen their costs of production, is the natural press of _competition_. Somebody else is offering this product, or will offer it, for less than we are now selling it for, and we must contrive some way by shortened times or cheaper processes or a quicker zeal not to be beaten in this market-race, is the silent argument ever making itself felt on the mind and hand of the producer. Such natural action always increases the general diversity of relative advantage as among buyers and sellers.