[cx01]

If there is only $100 in the economy, I can still owe you $105. To pay it back, I could start working for you and be paid $1 per hour. Now everytime you pay me $1, I would pay you back this dollar until my debt is zero.

In the real-world, with more than two persons, it would look more like this: I pay you back some amount of the debt, you spend this money and it propagates through the economy, until some part of it reaches me (in the form of a wage), so that I can use it to pay back more of the debt.

[stonemetal]

So you are saying the money pool expands at the rate in which the Federal Reserve spends money, and contracts at the rate it loans money?

[cx01]

No, I wanted to point out that the total amount of debt can be larger than the total amount of (physical) money.