Counters and sound changes: 本, 分, 冊, 回, 人 and dates

Why counting is harder than it looks

Spanish, French and English count by putting a numeral next to the noun and adding a plural: tres botellas, three bottles. Japanese nouns usually do not change for number, so it counts with a counter chosen by shape or kind, and the counter fuses with the numeral through two sound changes you already know from other words: sokuon (a small っ, as in がっこう) and rendaku (voicing, as in にほん → さんぼん; after ん the h of 分 becomes p instead: さんぷん). The changes hit 1, 3, 6, 8 and 10, and they are not optional.

The counters you meet first

Read the rows down. 1, 8 and 10 close into a small っ before h, k, s and t (いっぽん, はっさつ, じゅっかい); 6 does the same before h and k only (ろっぽん, ろっかい, but ろくさつ). 3 and 何 end in ん, which turns 本 into ぼん and 分 into ぷん (さんぼん, さんぷん, なんぼん, なんぷん). 人 keeps the old native ひとり・ふたり and then switches to the Chinese series, with よにん rather than よんにん.

Dates: the native series comes back

Days 1 to 10, plus 14, 20 and 24, use native readings: ついたち, ふつか, みっか, よっか, いつか, むいか, なのか, ようか, ここのか, とおか, じゅうよっか, はつか, にじゅうよっか. The rest are number + にち: じゅういちにち, にじゅうごにち. Months are number + がつ, but watch しがつ, しちがつ, くがつ, never よんがつ or ななげつ.

The sentences learners produce

• ✗ ビールをさんほんください → ビールを三本（さんぼん）ください. Rendaku is mandatory after 3.
• ✗ いちふん待って → 一分（いっぷん）待って. 1 before ふ・か・さ・た closes into っ.
• ✗ 学生がさんひといます → 学生が三人（さんにん）います. ひとり and ふたり are the only native forms.
• ✗ 本を三つ読みました → 本を三冊（さんさつ）読みました. つ is the fallback, but books, people, long things and minutes have their own counter.
• ✗ 三の本を買いました, copying tres libros → 本を三冊買いました. The counter goes after the particle, right before the verb; 三冊の本 is also possible, but never a bare 三の本.
• ✗ 四月（よんがつ）四日（よんにち） → 四月（しがつ）四日（よっか）. Months and days are separate systems.
• ✗ 一回目（いちかいめ） → 一回目（いっかいめ）. The っ survives when 目 is added.

A note on 4, 7 and 9

し and く are avoided in counting because し sounds like 死 (death) and く like 苦 (suffering). So よん and なな dominate with counters (よんほん, ななふん), but the fixed forms keep the old readings: よにん, しがつ, しちがつ, くがつ, and the clock says よじ, しちじ, くじ.