The joint services of money and credit

While credit cards provide transaction services, as do currency and demand deposits, credit cards have never been included in measures of the money supply. The reason is accounting conventions, which do not permit adding liabilities, such as credit card balances, to assets, such as money. But economic aggregation theory and index number theory are based on microeconomic theory, not accounting, and measure service flows. We derive theory needed to measure the joint services of credit cards and money. In the transmission mechanism of central bank policy, these results raise potentially fundamental questions about the traditional dichotomy between money and some forms of short term credit, such as checkable lines of credit. We do not explore those deeper issues in this paper, which focuses on measurement.