…, it is argued by some that financial institutions would be free to instantly transform their loans from the central bank into credit to the non-financial sector. This fits into the old theoretical view about the credit multiplier according to which the sequence of money creation goes from the primary liquidity created by central banks to total money supply created by banks via their credit decisions. In reality the sequence works more in the opposite direction with banks taking first their credit decisions and then looking for the necessary funding and reserves of central bank money.*1
In modern banking sectors, credit decisions precede the availability of reserves in the central bank. As Charles Goodhart pointedly argued, it would be more appropriate talking about a “Credit divisor” than about a “Credit multiplier”
In fact, the level of reserves hardly figures in banks’ lending decisions. The amount of credit outstanding is determined by banks’ willingness to supply loans, based on perceived risk-return trade-offs, and by the demand for those loans. The aggregate availability of bank reserves does not constrain the expansion directly. The reason is simple: as explained in Section I, under scheme 1 – by far the most common – in order to avoid extreme volatility in the interest rate, central banks supply reserves as demanded by the system. From this perspective, a reserve requirement, depending on its remuneration, affects the cost of intermediation and that of loans, but does not constrain credit expansion quantitatively. The main exogenous constraint on the expansion of credit is minimum capital requirements.
準備預金のアベイラビリティが制約にならないのは、"in order to avoid extreme volatility in the interest rate, central banks supply reserves as demanded by the system" すなわち、金利の激変を抑えるために需要に応じて準備預金を供給するためです。準備預金を調達できる金利の上限が分かっていれば、銀行は貸出に先立って市場の準備預金の量（の見通し）を気にする必要はありません。*2
In October 1979, under Chairman Paul Volcker, the FOMC changed its approach to monetary policy and began to target the quantity of money—specifically nonborrowed reserves. […] FOMC members expected that the new approach to monetary policy would result in greater volatility in the fed funds rate. This was indeed the result. […], the average fed funds rate fluctuated greatly between 1979 and 1982.
By the same token, under scheme 2, an expansion of reserves in excess of any requirement does not give banks more resources to expand lending. It only changes the composition of liquid assets of the banking system. Given the very high substitutability between bank reserves and other government assets held for liquidity purposes, the impact can be marginal at best.