Money

"Have you ever asked what is the root of money? Money is a tool of exchange, which can't exist unless there are goods produced and men able to produce them. Money is the material shape of the principle that men who wish to deal with one another must deal by trade and give value for value."
"Money rests on the axiom that every man is the owner of his mind and his effort. Money allows no power to prescribe the value of your effort except by the voluntary choice of the man who is willing to trade you his effort in return. Money permits you to obtain for your goods and your labor that which they are worth to the men who buy them, but no more."
"And when men live by trade – with reason, not force, as their final arbiter – it is the best product that wins, the best performance, then man of best judgment and highest ability – and the degree of a man's productiveness is the degree of his reward. This is the code of existence whose tool and symbol is money."

-Ayn Rand (Francisco's 'Money' Speech from "Atlas Shrugged")