Explicit Reasoning
This post is edited substantially in the hope of clarifying how credit flows increase, decrease, or do not increase or decrease the levels taken to be the statistical measures of the elastic money supply in the depository institutions.
The Financial Accounts Guide All Tables
https://www.federalreserve.gov/apps/fof/FOFTables.aspx
Scrolling down one observes financial statistics tables organized as Sectors: Transactions (links in the left side column) and Sectors: Levels (links in the right side column).
Transactions in these financial tables are classified as economic flows. These are financial flows caused by credit/debt deals.
Levels in these financial tables are economic stocks. The creditors own financial assets and the debtors owe liabilities or debts to the creditors. The flows of credit/debt deals increase or decrease the stocks of financial assets and liabilities because the financial tables are designed to be stock-flow consistent in accord with legal interpretations of credit/debt instruments and accounting customs for recording financial assets with matching liabilities.
Levels of Monetary Authority (Fed)
https://www.federalreserve.gov/apps/FOF/Guide/L109.pdf
Note three liabilities of the Fed are counted in the base money supply or monetary base also known as MB or M0:
Depository institution reserves
Vault cash of depository institutions
Currency outside banks
FRB H.4.1 Release shows Factors Supplying Reserve Balances including Reserve Bank credit and other assets listed on the Fed balance sheet:
https://www.federalreserve.gov/releases/h41/current/
FRB H.4.1 Release also shows Total factors, other than reserve balances, absorbing reserve funds including currency in circulation and all Fed liabilities other than reserve balances.
So Fed manages the level of reserve balances by using Reserve Bank credit to supply reserve balances when necessary if other factors absorb reserve balances. Some items on the balance sheet are autonomous, or not under the control of Fed, and other items are control factors such as levels of Reserve Bank credit. The flow of Reserve Bank credit is used as a control factor to supply levels of reserve balances against factors absorbing reserve balances as necessary to support the monetary policy goals of the Monetary Authority.
Levels of Private Depository Institutions
https://www.federalreserve.gov/apps/FOF/Guide/L110.pdf
Currently the first three lines are Total financial assets, Vault cash, and Reserves at Federal Reserve. Assume non-financial assets are negligible compared to the magnitude of financial assets. Then define Bank Credit:
Bank Credit = Total financial assets - Vault cash - Reserve balances
Depository institution liabilities are simplified by definition of Bank sector Liabilities* which are not classified as Checkable deposits:
Liabilities* = Total liabilities - Checkable deposits
The difference between bank assets and liabilities in the levels tables can be designated as equity claims or net worth to visualize a complete balance sheet:
Equity = Total Assets - Total Liabilities
Reasoning by analogy to the Monetary Authority balance sheet, which gives the factors supplying reserve balances and the factors absorbing reserve balances, the Depository institutions balance sheet would have factors supplying Checkable deposits and factors absorbing checkable deposits. We can write these factors in an identity as follows:
Checkable deposits = Reserve Balances + Vault Cash + Bank Credit - Liabilities* - Equity
where a transaction in the aggregate bank sector can increase or decrease Checkable deposit levels due to double-entry accounting customs. The sum of Checkable deposits and Currency outside banks is called the M1 money supply. The sum of Checkable deposits and items in Liabilities* is the M2, M3, etc. money supply. Liabilities* include items that are not counted in aggregate measures of the money supply so money supply is created, destroyed, or conserved depending on the nature of the transaction as a flow that supplies or absorbs or does not alter whatever definition of the "money supply" is applied for analysis.
Bank Credit Expansion or Contraction
${\Delta}$ Checkable deposits = ${\Delta}$ Bank Credit; or
${\Delta}$ Liabilities* = ${\Delta}$ Bank Credit; or
${\Delta}$ Equity = ${\Delta}$ Bank Credit;
In most cases the depository institution or bank sector originates credit by putting funds into the checkable deposit accounts of bank borrowers or bank customers who have sold financial assets to the bank. When bank sector sells a financial asset to units outside the sector, or when a bank customer outside the bank sector repays a loan the bank sector, the bank sector would reduce its sum of liabilities and equity and reduce assets listed in bank credit.