You use usury...
To return to a point raised by a couple of commentors, via Shakespeare again:
Merchant of Venice, Act 1, Scene 3.
[Aside] How like a fawning publican he looks!
I hate him for he is a Christian,
But more for that in low simplicity
He lends out money gratis and brings down
The rate of usance here with us in Venice.
Signior Antonio, many a time and oft
In the Rialto you have rated me
About my moneys and my usances:
Still have I borne it with a patient shrug,
For sufferance is the badge of all our tribe.
You call me misbeliever, cut-throat dog,
And spit upon my Jewish gaberdine,
And all for use of that which is mine own.
Well then, it now appears you need my help:
Go to, then; you come to me, and you say
'Shylock, we would have moneys:' you say so;
You, that did void your rheum upon my beard
And foot me as you spurn a stranger cur
Over your threshold: moneys is your suit
What should I say to you? Should I not say
'Hath a dog money? is it possible
A cur can lend three thousand ducats?' Or
Shall I bend low and in a bondman's key,
With bated breath and whispering humbleness, Say this;
'Fair sir, you spit on me on Wednesday last;
You spurn'd me such a day; another time
You call'd me dog; and for these courtesies
I'll lend you thus much moneys'?
Now, note above, the christian lends money gratis to his friends.
Lets look at this closer, in terms of Mauss' ideas on gift relations. If I lend someone money, I am not making a gift of it, so it's return to me does not count as an equivilant gift. i.e. if I gave someone money that person some money, the gift relationship wopuld require them to give me a gift of the same value/sort at a later date, and that would be it.
When I lend money, I expect to get it back anyway, what I am giving is my trouble in not having my own money to hand. The person who borrows owes me recompense for that trouble, to reciprocate the gift or face the shame of charity/inability to reciprocate.
Now, usury allows for this by making it a purely monetary payment. When Antonio in the Merchant of Venice lends money he does so to his friends, that is the polite gloss of talking about his network of dependence and clientalism that made up his place in feudal society, the people he lends money to may pay back only that monetary value, but they owe him gratitude. Again, the sin of the Jew figure is to monetize social/personal relations and thus dissolve feudal loyalty. Hence the plays triumphant denument when racial law is used to stop the base abstraction of Shylock's contract.
Anyway, my point is this, you cannot have money lending without usury, without interest of some sort, whether its called that or not.
As an aside, next month's Socialist Standard has a small article on Islamic interest making much the same point.