Where you are. You can follow a payment through five parties, watch a clearing house shrink a day’s obligations to a handful of net ones, and you own the two words lesson 5 coined: settlement, the moment a ledger edit becomes final, and reserves, a bank’s own balance at the central bank. This lesson stops following payments and draws the map they all move across. Every form of money you have met so far gets a fixed place on it, and every later module points back at it.
Where, exactly, is your money?
Open your banking app and look at the balance. Now chase it.
The number on the glass is pixels, rendered from a JSON response. The response came from your bank’s API. The API read a row in a database your bank operates. Stop the chase there for a moment, because the row deserves a stare: it is not a pointer to your money, held somewhere else. There is no vault behind it with your name on a shelf. The row is the money. You met this idea as a notched stick in lesson 2; here it is again, wearing a primary key.
Chase once more. Your bank holds money of its own - it settles with other banks every day, and it needs something to settle in. Where does the bank’s money live? Same answer, one hop up: a row in a database the central bank operates. That balance is the bank’s reserves, the word you took from lesson 5.
Chase a third time. Where does the central bank’s money live? Nowhere further. A reserve balance is not a claim on some deeper ledger; there is no third database standing behind the second. The recursion stops. Two hops from your phone screen, you have hit the floor of the entire system.
The idea in one paragraph
Every form of money is an entry on somebody’s ledger, and the ledgers form exactly two tiers. Tier 1 is the central bank’s ledger: reserves and banknotes live there, and it is where banks settle. Tier 2 is the commercial banks’ ledgers: deposits live there, and it is where everyone else pays. Anything else that behaves like money - a balance in a payment app today, grander things later in the course - is a private claim on one of those two tiers, bolted onto the side of the map rather than given a tier of its own. To place any form of money, ask one question: whose ledger does it live on? The rest of this course is spent moving entries around this map, which is why this is the lesson to keep.
Sort by the liability, not the location
The sorting question needs one accounting word. A liability is an amount the issuer owes: an entry in the issuer’s own books that says “we owe this”. Your deposit is an asset to you and, simultaneously, a liability of your bank - the goldsmith’s IOU from lesson 3, now a database row instead of paper. Every form of money is somebody’s liability. Sort by the somebody and the whole system falls into two tiers.
Tier 1: the central bank’s ledger. Two things live here: reserves, each bank’s own balance, and banknotes, the same promise issued in physical form. The account holders are a short list - banks and a few other institutions - and the writes are few. This is where settlement happens: when two banks square a day’s obligations, reserves move on this ledger, and the move is final.
Tier 2: the commercial banks’ ledgers. Deposits live here: yours, your employer’s, the coffee shop’s. Pay someone who banks where you bank and one ledger edits twice; tier 1 never hears about it. Pay across banks and tier 2 edits at both ends while the banks settle the difference on tier 1 - the clearing house pattern from lesson 4, netting a day of payments down to a few reserve moves.
Notice what makes tier 1 the floor. Every claim on the map points at something its issuer must produce on demand. A deposit points at central-bank money: ask for cash and your bank owes you banknotes; pay across banks and it owes reserves. Central-bank money points at nothing beyond itself: present a banknote at the central bank and the most it will owe you is a fresher banknote. Reserves settle everything; nothing settles reserves. Software has a name for this - the base case - and it is why the chase from your phone had to terminate.
The three kinds of money, by name
The course reaches for this three-way distinction constantly from here on, always by these names, so take them now.
Central-bank money is what lives on tier 1: reserves and banknotes, the liabilities of the central bank. A banknote is the bearer form of the promise - bearer meaning whoever holds it owns it, no account required.
Commercial-bank money is what lives on tier 2: deposits, the liabilities of commercial banks. It is most of what anyone means by “my money”, and it is where nearly all payments start and finish.
Private claims on either is everything issued by somebody who is neither. The first resident of this box is e-money: a prepaid balance in a payment app, issued by a company that is not a bank, and therefore that company’s liability rather than a bank’s. Later lessons add more residents. It is not a third tier, because everything in the box promises to pay out in money from one of the two tiers.
Here is the whole lesson as one drawing. When a later lesson says “tier 1” or “tier 2” without ceremony, this is the map it means.
Wider than the screen; scroll it sideways.
Check yourself
1. A banknote in your pocket never touches a computer, let alone a database. Why is it tier 1?
Because the map sorts by liability, not location. The note is the central bank’s promise in bearer form: whoever holds it, the central bank owes it. Moving it from a vault to your jeans changes who holds the claim; it cannot change who owes it, and who owes it is what decides the tier.
2. Why does the chase from your phone screen stop after exactly two hops?
Each claim points at what its issuer must produce: a deposit points at central-bank money, so the first hop lands on your bank’s reserves. But central-bank money points at nothing beyond itself - present a banknote to the central bank and you are owed, at most, another banknote. Tier 1 is the base case: it settles every claim above it and is settled by nothing.
3. A deposit and an e-money balance both appear as a number in an app. What separates them on the map?
Whose liability each one is. The deposit is a commercial bank’s liability, native to tier 2. The e-money balance is a private issuer’s liability: a claim on the issuer, whose backing is itself a deposit at a bank. That extra link is why the map draws private issuers as a side box - a claim on a claim - rather than a third tier.
Do this
Ten minutes, standard library only. Open code/whose_ledger.py: four instances of money and an empty TIER_OF dictionary. Classify each instance as tier 1 or tier 2 by asking the lesson’s question - whose liability is it? Note the file’s convention: tier 2 means any commercial ledger, a bank’s or a private issuer’s, so the side box files under 2 here.
python3 code/whose_ledger.pyRun unmodified, the starter stops at classify every instance. Classified correctly, it prints both tiers and ends with the line
an e-money balance in a payment appunder the TIER 2 heading. If the second assert fires instead, at least one placement was sorted by location or by feel; re-ask the liability question for that instance. The completed version is in solutions/whose_ledger.py.
What you can now do. You can place anything that calls itself money on the two-tier map with one question: whose ledger does it live on; equivalently, whose liability is it. You can name the three kinds the course will keep using - central-bank money, commercial-bank money, and private claims on either - and you can say why every chase through the system bottoms out at the central bank’s ledger, two hops from your phone screen. The next lesson returns to the five-party payment from lesson 1 and asks the question the rest of the course keeps testing: what changes if the message itself is the money?