Reference · じょすうし — counters

Counters, and which ones change

Nine counters, six chapters, ninety readings. Tap any of them to hear it. The thing worth carrying away is not the table — it is the one question you can ask before the table.

Readings checked against Wikipedia's counter tables and against this course's own lessons · verified by check_counters.py, which predicts every regular cell rather than trusting it

1.Ask this first

Look at the counter's own first sound. That decides whether it changes at all — before you know which number you are attaching.

The counter starts…	Then	Which ones
on a vowel	Nothing can happen. There is no consonant to double against and none to harden.	〜えん
voiced — が, じ, に	Nothing happens either. It is already voiced; there is nothing left to do to it.	〜がつ　〜じ　〜にち　〜にん　〜ばんせん
voiceless — か, さ, ふ	These are the ones that change. All three of them do, and no others in this course.	〜かい　〜さい　〜ふん

Trick 1 · The rule predicts counters you have not met yet

This is worth more than the table below, because it works forward. 〜ほん (long thin things), 〜さつ (books) and 〜こ (small objects) all start voiceless — so expect them to fight. 〜だい (machines) and 〜ど (times) start voiced, so expect them to behave.

You will still have to learn which numbers do it. But you will never be surprised by whether.

It has now been tested twice. This sheet predicted 〜にん would behave before the readings were written down, and when chapter 15 wrote them down it did: eight of its ten cells are the plain number joined on, and the two odd ones are old words rather than sounds. Then chapter 16 brought 〜ばんせん, the platform number — voiced again, and this time ten cells, zero marks: the first counter on the sheet the rule clears completely.

2.The two changes, and the numbers that cause them

Only two things ever happen, and they can happen together.

Change	Mark	What it does	Caused by
Gemination	っ	The number's last mora collapses to a small っ: いち → いっ, ろく → ろっ, はち → はっ, じゅう → じゅっ	1, 6, 8, 10 — the four numbers that end in a consonant-heavy mora
Hardening	ぷ	A は-row sound becomes a ぱ-row one: ふ → ぷ	After a っ and after ん — so 1, 3, 4, 6, 8, 10
Voicing	が	A か-row sound becomes a が-row one: かい → がい	3 only, and only for 〜階 in this course

The exception that earns its keep

ろく geminates before か and ぱ sounds — ろっかい, ろっぷん — but not before さ. Six years old is ろくさい, never ろっさい.

It is the only place in the table where one of the four gemination numbers declines to geminate, so it is the one cell worth memorising on its own.

Trick 2 · The same rule read from the number's side

Section 1 asks what the counter starts with. Ask instead what the number ends with, and the whole table above collapses into three groups:

にごななきゅう end in a vowel — and never change anything, in any column of this sheet. That is four tenths of every counter table, gone.
いちろくはちじゅう end in ち・く・う — they collapse to っ.
さんよんなんせん end in ん — they reach forward and change a は-row counter.

The first line is the useful one, and it is exceptionless across all nine counters here — check_counters.py asserts it, so a tenth counter that broke it could not be added quietly. Chapter 15 builds the numbers this way round.

A different thing entirely: よ・し, しち・なな, く・きゅう

Marked ✱ in the table. These are not sound changes — よじ is not よんじ worn down, it is a different word for four. Filing them with the sound changes sends you looking for a phonetic reason there isn't one.

The split is per counter and has to be learned per counter: 〜じ and 〜がつ take よ／し, しち and く; 〜さい, 〜かい and 〜ふん take よん, なな and きゅう.

3.All nine, 1 to 10

The two tables are the two groups from section 1, and the shading tells you the split was worth making: the first table has none and the second is covered in it.

The flag after a reading says which change: っ gemination, ぷ hardening, が voicing, ✱ a different number word or a native numeral. Tap any reading to hear it — this whole sheet is about sound, and the page can say all ninety.

The table needs JavaScript. Every reading in it is also in the lesson its column names, listed under section 4.

The bottom row is the question form. It is the cheapest evidence the sheet contains: なんがい is voiced and なんぷん is hardened, which is how you can tell that さんがい and さんぷん are real without anyone telling you. Chapter 13 derived its rendaku exactly this way.

4.One line on each

The notes need JavaScript. Each counter's own lesson carries the same information in full.

5.The days are a different problem

〜にち is on the table above for comparison, but it is not a sound-change counter at all. Days 1 to 10 use a native Japanese counting series that has nothing to do with いち・に・さん — and then 14, 20 and 24 keep pieces of it after the rest have gone over to the regular readings.

That is a memorising job rather than a rule, and it has its own sheet: the calendar reference carries all 31 days with the irregulars marked, plus the months and the weekdays.

6.What is still open

Lesson 6 taught the なん〜 question for eleven counters, long before the course had the counters to answer them with. Six have since been answered. These have not:

Question	Asks for	Counter not yet taught
なんねん	which year	〜ねん
なんじかん	how many hours	〜じかん
なんしゅうかん	how many weeks	〜しゅうかん
なんかげつ	how many months	〜かげつ

Two of those start voiceless — 〜かげつ and 〜しゅうかん — so section 1 predicts they will change when they arrive. 〜にん used to be on this list with the prediction that it would not; chapter 15 taught it and the prediction held, so it has moved up into the table.

7.Sources

Japanese counter words — read this one if you read one. It is where every reading here was checked, and it carries the several hundred counters this course has not reached, with the same euphonic changes running through all of them.
Japanese numerals for the two number series — the Sino-Japanese いち・に・さん and the native ひと・ふた・み that the days of the month are the last common survival of.
The counters' own lessons: 10 for 〜がつ and 〜にち, 11 for 〜さい, 13 for 〜階 and 〜円, 14 for 〜じ and 〜ふん, and 16 for 〜番線.
The calendar sheet for all 31 days, and the question-word sheet for the なん〜 forms in section 6.