Debt, inflation and the exchange rate
As noted above, debt is normally denominated in a particular monetary currency, and so changes in the valuation of that currency can change the effective size of the debt. This can happen due to inflation or deflation, so it can happen even though the borrower and the lender are using the same currency. Thus it is important to agree on standards of deferred payment in advance, so that a degree of fluctuation will also be agreed as acceptable. It is for instance common to agree to "US dollar denominated" debt.
The form of debt involved in banking accounts for a large proportion of the money in most industrialised nations (see money and credit money for a discussion of this). There is therefore a complex relationship between inflation, deflation, the money supply, and debt. The store of value represented by the entire economy of the industrialized nation itself, and the state's ability to levy tax on it, acts to the foreign holder of debt as a guarantee of repayment, since industrial goods are in high demand in many places worldwide.