When a central bank is "easing", it triggers an increase in money supply by purchasing government securities on the open market thus increasing available funds for private banks to loan through fractional-reserve banking (the issue of new money through loans) and thus grows the money supply.

When the central bank is "tightening", it slows the process of private bank issue by selling securities on the open market and pulling money (that could be loaned) out of the private banking sector. It reduces or increases the supply of short term government debt, and inversely increases or reduces the supply of lending funds and thereby the ability of private banks to issue new money through debt.

The operative notion of easy money is that the central bank creates new bank reserves (in the US known as "federal funds"), which let the banks lend out more money. These loans get spent, and the proceeds get deposited at other banks. Whatever is not required to be held as reserves is then lent out again, and through the "multiplying" effect of the fractional-reserve system, loans and bank deposits go up by many times the initial injection of reserves.

However, in the 1970s the reserve requirements on deposits started to fall with the emergence of money market funds, which require no reserves. Then in the early 1990s, reserve requirements were dropped to zero on savings deposits, CDs, and Eurodollar deposit. At present, reserve requirements apply only to "transactions deposits" – essentially checking accounts.

The vast majority of funding sources used by private banks to create loans are not limited by bank reserves. Most commercial and industrial loans are financed by issuing large denomination CDs. Money market deposits are largely used to lend to corporations who issue commercial paper. Consumer loans are also made using savings deposits, which are not subject to reserve requirements. These loans can be bunched into securities and sold to somebody else, taking them off of the bank's books.

Therefore, neither commercial nor consumer loans are any longer limited by bank reserves. Since 1995 the amount of consumer loans has steadily increased, while bank reserves have generally remained constant: