熟語の構成: the 5 types of Japanese compound words

The 5 types of 熟語の構成 at a glance

The labels ア to オ come from the 漢検 answer sheet, and most Japanese study material borrows them. Keep this table open while you read the rest. Each row has a one-line test, and the tests are what you'll actually use.

Type ア: two kanji with similar meanings

The simplest pattern. Both kanji point at the same idea, and the compound is that idea, said twice for weight and clarity. 道 is a way, 路 is a route, and 道路 is a road.

Japanese builds a lot of formal vocabulary this way, especially verbs-turned-nouns: 増加, 製造, 救助. If you know one kanji, you can usually guess the whole word.

Type イ: opposite or paired meanings

Two kanji that pull in opposite directions, and a compound that covers the whole range between them. 高低 is "highs and lows", 売買 is buying and selling, the whole trade.

"Paired" matters as much as "opposite". 左右 and 往復 aren't good-versus-bad, they're two halves of one thing. That still counts.

Type ウ: the first kanji describes the second

This is how English adjectives work. 白紙 is white paper, 黒板 is a black board. The second kanji is the thing, the first tells you which one.

It works with adverbs too. 再開 is 再び開く, opening again. Turn the first kanji into an い-adjective, add の, or use its adverb form, and if the result is a natural phrase, you've found ウ.

Type エ: an action and its object

Japanese puts the verb last: 本を読む. Chinese, where this word pattern comes from, puts it first. So a type エ compound is a tiny Chinese sentence: action first, object second. 読書 is 読 (read) + 書 (book).

That gives you the most reliable test in the whole topic. Read the word backwards and put を or に between the kanji. 書を読む. 山に登る. 席に着く. If you get a sentence you could actually say, it's エ.

The に cases trip people up, because "object" sounds like を only. The 漢検 wording is 目的語・補語, object or complement, so destinations count: 車に乗る, 国に帰る.

Type オ: the first kanji cancels the second

The fastest type to spot. If a two-kanji word starts with 不, 無, 未 or 非, the first kanji is negating the second: 不安 is "not at ease", 無害 is "no harm".

The same four prefixes go on longer words too, and that's where they earn their keep for the JLPT. Each one has its own flavour, and a word only takes one of them:

The easy one to mix up is 不 versus 未. 未 means "not yet", so it carries a hint that it'll happen: a 未完成 painting is still being painted. 不 just says it isn't so. When a word could take both, ask whether the thing is expected to change.

The sixth type you'll find in school textbooks

Japanese junior-high 国語 textbooks often teach one extra pattern: 主語・述語, subject and predicate. The first kanji is the subject, and the second says what it does. Read it as 前が後する.

The 漢検 five-choice format doesn't list this one, which is why it's not in the table above. If you're studying from a school book, add it as type 6. If you're preparing for 漢検, five is enough.

How to classify any Japanese compound word in 4 steps

Work through the types in this order. The first two have mechanical tests, so you can rule them in or out in seconds and leave the judgement calls for last.

1. 01

   Look for 不, 無, 未 or 非 at the front

   If one of the four is there and it negates the second kanji, you're done. It's オ.

   未定 → 未 + 定 → オ
2. 02

   Flip it and add を or に

   Say the second kanji, then を or に, then the first kanji as a verb. A natural sentence means エ.

   読書 → 書を読む → エ
3. 03

   Make the first kanji describe the second

   Try い, の or an adverb: 白い紙, 国の内, 再び開く. If it works, it's ウ.

   黒板 → 黒い板 → ウ
4. 04

   Compare the two meanings

   Same idea means ア. Opposite ends or two halves of a pair means イ.

   救助 → save + help → ア

Most wrong answers come from skipping step 2. Students see an action-looking kanji and go straight to "it describes the second one", or decide two verbs must be similar. Say the backwards sentence out loud. It takes two seconds, and it settles エ either way.

Is 熟語の構成 on the JLPT?

Not by name. No JLPT question asks you to pick type ア or type エ. That question format belongs to the 漢検, the Japan Kanji Aptitude Test, where 熟語の構成 is its own section with exactly the five choices above.

So why bother if you're sitting the JLPT? Two places it pays off. The N2 vocabulary section has word-formation (語形成) questions, where you pick the prefix or suffix that fits, and the four negative prefixes from type オ are regulars. And in N2 and N1 reading you'll hit compounds you've never studied. If you can see that 減税 is 税を減らす (cutting taxes), you don't need the dictionary.

It also makes kanji stick. A word with a structure is easier to remember than two random characters. Pair this with the routine in how to study JLPT vocabulary with flashcards, and when you meet a new compound on a card, name its type before you flip.

熟語の構成 practice: 12 questions

Pick the type for each word. You'll see the answer straight away. Use the 4-step method, and say the backwards sentence for any word that might be エ.

1. Q1 がんせき

   岩石

   ア イ ウ エ オ
2. Q2 ぜんあく

   善悪

   ア イ ウ エ オ
3. Q3 はくし

   白紙

   ア イ ウ エ オ
4. Q4 とざん

   登山

   ア イ ウ エ オ
5. Q5 きゅうじょ

   救助

   ア イ ウ エ オ
6. Q6 だいしょう

   大小

   ア イ ウ エ オ
7. Q7 こくばん

   黒板

   ア イ ウ エ オ
8. Q8 せんがん

   洗顔

   ア イ ウ エ オ
9. Q9 みてい

   未定

   ア イ ウ エ オ
10. Q10 ちゃくせき

    着席

    ア イ ウ エ オ
11. Q11 ていし

    停止

    ア イ ウ エ オ
12. Q12 むがい

    無害

    ア イ ウ エ オ