Fractional reserve banking is sometimes portrayed as a sort of scam; a method by which rich bankers underhandedly sap the wealth of society. This short video here, How Fractional Reserve Banking Increases Inflation and Steals our Wealth , is fairly representative of a view I hear expressed quite often.As you might have guessed, I think that this view is somewhat distorted and misleading. Let me explain why I feel this way.The video starts off with an hypothetical depositor who starts off with $1000 and asks what happens when it is deposited. Right away we are off to a poor start.Does he mean starting off with $1000 of cash? Or does he mean $1000 of money (say, in the form of a paycheck)? It makes a difference. When was the last time you made a cash deposit? If you are like me, you cannot remember when. Of course, money gets "deposited" all the time in your account. At work, for example, you might be paid by check or by direct deposit. But this is not what the guy means by "making a deposit"--these "deposits" are simply debit and credit operations in a linked system of accounts (your paycheck is credited to your account, and is debited from your company's account). What the guy means by a "deposit" is a cash deposit. The main source of cash deposits in all likelihood originates from the cash registers of retail businesses.Alright then, evidently there is cash in circulation. These days, cash primarily takes the form of small denomination paper notes issued by a central bank, like the Fed (in the past, cash frequently took the form of specie--gold and silver coin). There is a demand for cash. Cash is useful for purchasing some types of goods and services when no other means of payment is available. (Cash is also used when transactors wish to keep their exchanges anonymous). And so people occasionally visit ATMs to make cash withdrawals. This cash ultimately finds its way in the cash registers of businesses (however, it is estimated that a lot circulates in the underground economy and, in the case of the U.S., outside of the country).O.K., so where does banking fit in all this? Maybe your ideal view of a bank is simply as a place to keep your cash safe, kind of like your piggy bank. You deposit your cash with the bank, and the bank issues you a receipt, which constitutes a record of your cash deposit and represents a claim for cash (deliverable by the bank). Or the bank may simply record your deposit as a book entry item. Either way, your cash deposit constitutes a liability for the bank. These liabilities are sometimes called "bank-money" because, well, because they can be used as money. Receipts (especially if they are made payable to the bearer) can potentially circulate as money. Similarly, checks can be written ordering the transfer of cash sitting at the bank from one account to another. If the value of liabilities issued by the bank do not exceed the amount of cash it holds as assets, then we call this 100% reserve banking. (The liabilities issued by the bank are backed 100% by cash.)Of course, banks do not just keep your cash safe and perform debit/credit transactions for you. They also make money loans. And here is where the confusion generally begins. It starts with the idea that the bank might have the temerity to lend YOUR cash out to someone else--at interest, to boot!Well, that's not quite what happens. Let try me explain (well, to the best of my understanding, of course).Suppose you want to start a restaurant business. You own the property and building, but nothing else (apart from your human capital). The building needs to be made into a restaurant. You need ovens, utensils, rooms to be made and finished, furniture, staff, advertising, accountants, lawyers, etc. How do you pay for all this stuff? You clearly have wealth (physical and human capital). You just don't have any cash.But what do you need cash for anyway? Why not pay for all this stuff using your wealth? One way to do this, in principle at least, is to issue receipts representing shares in your wealth. These shares are liabilities against your wealth. Each share represents an IOU against the future income stream generated by your capital. (The IOUs could take a variety of forms. They could, for example, be made into coupons redeemable for food from your restaurant--something very similar to Canadian Tire Money ).Um, one problem. If you're like me, not very many people know who you are. A randomly selected member of society is unlikely to recognize us, or have any idea what we really own, or have any idea how well we might live up to the promises (IOUs) we issue. Basically, most of us are(except for within a relatively small network of friends and business relations--and even then, we keep a lot of information private).(it is not easily or widely accepted as a means of payment).O.K., so scratch the idea of creating your own money. This is where a bank now comes in. Let's imagine that the bank reviews your business proposal and concludes that it is likely to be profitable. The bank also thinks that your capital is of high quality and that your ownership title is clear (btw, you are now no longer anonymous to the bank). Now, you might think that the bank is then going to lend you the cash you need to finance your operations. Well, you would be wrong (sort of). That is, you do not need cash--what you want is bank-money. And that's what you typically get from the bank: a money loan in the form of bank liabilities (not cash).Now, the commentator in that video claims that this bank-money is created out of thin air. That is both correct and completely irrelevant; see my earlier post here . The bank-money (whether in the form of paper notes or book-entry objects) are backed by the assets you put up as collateral for your loan. As long as the loans officer makes good decisions about which business ventures to lend money to, the bank-money created by the bank is fully backed (and consequently, not inflationary; i.e., the new money issue is not dilutive).. This is hardly an activity that one might reasonably label as being inherently "evil."But this is not quite the end of the story. I have just made the claim that banks issue fully-backed liabilities that serve as money instruments. If this is true, then what do people mean by fractional reserve banking? Let me explain.In practice, banks issue a very peculiar type of liability, called a demand-deposit liability. In the lingo of financial wonks, these are liabilities that have embedded within them a contractual stipulation known as an American put option . This option gives the debt holder (the depositor) the right to exercise a redemption option on demand at a fixed price. The redemption option in this case consists of the right to redeem bank-money for cash on demand (and usually at par, but frequently subject to a service charge). This is what happens every time you make a withdrawal of cash from your bank or an ATM.I don't know why banks do this. In many jurisdictions, it may constitute a legal restriction (as part of the bank charter). I'm not sure if the restriction is binding, however. That is, it is my understanding that banks used to do this even when they were not legally required to do so. Evidently, the redemption option is valued by those who make use of bank-money.I am aware of only two (not necessarily mutually exclusive) explanations for this contractual stipulation. One is that consumers value insurance against "liquidity shocks" (events were only cash is accepted). The other is that the redemption option serves as sort of a discipline device for bank managers (see Calomaris and Kahn, AER 1991). That is, the put option makes the bank's liability a, so that depositors can potentially pull out very quickly if they sense any hanky-panky. The threat of mass redemptions (and the bankruptcy it would entail) is presumably enough to dissuade self-interested bankers from absconding with depositor wealth.Sounds wonderful except that, of course, only a very small fraction of a bank's assets are typically in the form of cash. Most of the bank's assets are tied up in "long-term illiquid" assets, like your house, or your human capital. Consequently, while the bank's liabilities may be fully backed, only a small part of this backing is in the form of cash. This is the true nature of fractional reserve banking.The potential trouble, of course, comes to play when a bank (or worse, the banking system as a whole) is subject to a wave of mass redemptions. There is simply not enough cash in the banking system to honor all of its short-term debt obligations simultaneously. (This is not fraud or deceit; it is something that everyone is--or should be--plainly aware of.) In this event, banks are compelled to sell off their assets to raise the cash they need. This is not something that all banks can all accomplish simultaneously; at least, not without depressing asset values and creating a deflation (the fall in the price-level reflects an increase in the demand for, hence value of, cash relative to goods and services).There are basically two (possibly more, as readers have suggested below) ways to eliminate retail-level banking panics (waves of mass redemptions). Neither are without cost. One way is to adopt some sort of national deposit insurance system. This is the system that presently exists in the United States (FDIC plus the Fed discount window). People criticize this system because it allegedly promotes moral hazard (banks are induced to take on excessively risky investments). On the other hand, the U.S. has not experienced a retail-level bank run since the Great Depression.The other way to eliminate retail-level banking panics is to pass legislation requiring all banks to hold 100% cash reserves. This would, of course, kill the business that transforms your illiquid assets into a liquid payment instruments. But it would not necessarily kill the prospect of bank-run-like phenomena. This is because bank-run-like phenomena can emerge even without fractional reserve banking. The phenomenon is possible whenever short-term debt is used to financed long-term (illiquid) asset purchases, as is the case in the wholesale-level banking sector (the so-called "shadow banking" sector).The use of short-term debt to finance long-term asset purchases (think of the overnight repo market) is, again, a very peculiar financing structure. Like the demand deposit liability, the structure is likely explained by the need to align incentives. While this structure may enhance efficiency along some dimension, it comes at a cost. The analog to a bank run here is a "roll over freeze." This is an event where creditors (depositors) refuse to rollover their short-term funding. In this event, debtors must now scramble to raise funds or dispose of their assets (at "firesale" prices).If this sounds familiar, it should: it is exactly what happened in our most recent financial crisis. It is also what policymakers currently fear might happen to European banks (who have borrowed USD short-term, to finance longer-term asset purchases; see here ).