Those of you who came to libertarianism like I did, through economics, probably have a special fondness for the idea of transactions. Transactions are the great equalizer and maker of friends. Any two people who trade are acting as partners and both benefit or they wouldn't participate. The objectivists especially emphasize the difference between transaction and theft as a conceptual tool for illustrating the difference between market and government. It may come as a surprise therefore, when I say that transactions are not the atom of economics, gifts are.
Transactions are just gifts bound together in pairs like the atoms of nitrogen in the air.
Just as nitrogen is inert when the atoms are paired, transactions are tremendously useful compared to other gift giving customs. We give away our money to strangers because we have the expectation that these strangers will then give us merchandise. Without this pairing we would have to individually know and trust everyone we dealt with. Only in small groups like families and tribes can this be the case. Gifts also provide a way to extend the idea of a free market to primitive cultures.