Now that you know Japanese relative clauses carry no relative pronoun, we can split them into their two fundamental types. This page covers the first and most common: the 内（うち）の関係（かんけい）, the "inner relation" or gap type. In a gap-type clause, the head noun corresponds to a missing slot inside the clause — it could slide back into the clause and fill an argument position. 私（わたし）が読（よ）んだ本（ほん） ("the book I read") lines up with 私が本を読んだ ("I read the book"), where 本 is the object of 読む. That correspondence — a hole in the clause exactly the size of the head noun — is what defines the type.
The head noun fills a gap
In a gap-type clause, the modifying clause is incomplete: one of its arguments is missing, and the head noun is precisely the thing that would fill that hole. English relative clauses work the same way underneath — "the book [that I read ]" has a gap after read — but English plugs the gap's front end with a relative pronoun (that), while Japanese leaves the gap completely empty and silent.
子供が描いた絵を壁に飾った。
kodomo ga kaita e o kabe ni kazatta
We hung the picture the child drew on the wall.
The clause 子供が描いた ("the child drew _") is missing its object. The head noun 絵 ("picture") is exactly that missing object: 子供が絵を描いた ("the child drew a picture"). The head has been lifted out of the clause and set at the front, leaving a gap where it used to be.
田中さんが住んでいる町はとても静かだ。
Tanaka-san ga sunde iru machi wa totemo shizuka da
The town where Tanaka lives is very quiet.
ケーキを食べた人は名乗り出てください。
kēki o tabeta hito wa nanoridete kudasai
Whoever ate the cake, please come forward.
The un-relativize test
Here is the diagnostic that makes this type precise — and it is the single most useful tool in this whole subgroup. Take the head noun and try to put it back into the clause with an appropriate particle. If you can rebuild a complete, natural sentence, the clause is 内の関係 (gap type).
| Modifier + head | Un-relativized (head reinserted) | Head's role |
|---|---|---|
| 私が読んだ本 | 私が本を読んだ | object (を) |
| 子供が描いた絵 | 子供が絵を描いた | object (を) |
| ケーキを食べた人 | 人がケーキを食べた | subject (が) |
| 田中さんが住んでいる町 | 田中さんが町に住んでいる | location (に) |
| 手紙を書いたペン | ペンで手紙を書いた | instrument (で) |
Each row rebuilds into a full sentence, so each is a genuine gap-type relative clause. Notice the head noun can fill any grammatical role — subject, object, location, instrument — and the test still works; you just have to supply the right particle when you reinsert it.
私が生まれた病院はもう建て替えられた。
watashi ga umareta byōin wa mō tatekaerareta
The hospital where I was born has already been rebuilt.
この手紙を書いたペンはどこ？
kono tegami o kaita pen wa doko
Where's the pen I wrote this letter with?
In 私が生まれた病院, reinsert 病院 with に → 私が病院で生まれた, a fine sentence, so it is gap type (the head is the location of being born). In この手紙を書いたペン, reinsert ペン with で → このペンで手紙を書いた, again fine, so it is gap type (the head is the instrument).
The head can play any role — mind the particle
Because the gap can be any argument, the same-looking structure can mean quite different things depending on what role the head plays. This is where the un-relativize test pays off, because it forces you to identify the particle the head would carry.
| Head's role in the clause | Example | Meaning |
|---|---|---|
| subject (が) | 昨日来た友達 | the friend who came yesterday |
| object (を) | 母が作った料理 | the dish my mother made |
| location (に／で) | みんなが集まる場所 | the place where everyone gathers |
| time (に) | 彼に会った日 | the day I met him |
| instrument (で) | 手紙を書いたペン | the pen I wrote the letter with |
みんなが集まる場所を教えてください。
minna ga atsumaru basho o oshiete kudasai
Please tell me the place where everyone gathers.
彼に初めて会った日のことは今でも覚えている。
kare ni hajimete atta hi no koto wa ima demo oboete iru
I still remember the day I first met him.
English marks all of these with different words — who, which, where, when, with which — but Japanese uses the identical bare-clause structure for every one. The role lives implicitly in the gap; you recover it by asking what particle the head would take on reinsertion.
Why the test matters: it separates gap from gapless
Everything above builds to this. Not every noun-modifying clause has a gap. There is a second type — the 外（そと）の関係 ("outer relation," gapless type) — where the head noun is not an argument of the clause and cannot be reinserted. The two types look identical on the surface (plain clause + noun), so learners routinely confuse them. The un-relativize test is what tells them apart cleanly:
魚を焼くにおいが部屋に充満していた。
sakana o yaku nioi ga heya ni jūman shite ita
The smell of grilling fish filled the room.
Try the test on 魚を焼くにおい ("the smell of grilling fish"). Can you reinsert におい into 魚を焼く with a particle? ×においを魚を焼く — no. ×においで魚を焼く — no. におい is not an argument of 焼く ("grill") at all; there is no gap for it. So this is not 内の関係 — it is the gapless 外の関係, where the clause describes the content of the head rather than filling a slot in it. That whole gapless type gets its own treatment on the outer-relation page.
The tense on these gap-type clauses is read relative to the main clause, not the moment of speaking — 会った日 can point to a past or future day depending on the outer verb — a point developed on the tense in modifying clauses page.
Common mistakes
Mistake 1 — Still expecting a relative pronoun. The gap is silent; nothing marks it.
❌ 私がそれを読んだ本
Wrong — don't fill the gap with a resumptive それ. The gap stays empty: 私が読んだ本.
✅ 私が読んだ本
watashi ga yonda hon
the book I read
Mistake 2 — Repeating the head noun inside the clause. Overtly filling the very gap the head vacated.
❌ 子供が絵を描いた絵
Wrong — 絵 already left a gap as the object; don't restate it inside. Just 子供が描いた絵.
✅ 子供が描いた絵
kodomo ga kaita e
the picture the child drew
Mistake 3 — Assuming the head's role is always object. The gap can be subject, location, or instrument, and the particle changes.
❌ 田中さんが住んでいる町 → 田中さんが町を住んでいる
Wrong reinsertion — 町 is a location, so it takes に, not を: 田中さんが町に住んでいる.
✅ 田中さんが住んでいる町
Tanaka-san ga sunde iru machi
the town where Tanaka lives
Mistake 4 — Treating a gapless (外の関係) clause as if it had a gap. Forcing a reinsertion that doesn't exist.
❌ 魚を焼くにおい → においを魚を焼く
Wrong — におい can't reinsert into the clause; there is no gap. This is the gapless 外の関係 type, not a true relative clause.
✅ 魚を焼くにおい
sakana o yaku nioi
the smell of grilling fish
Key takeaways
- The 内の関係 (gap type) is the prototypical relative clause: the head noun corresponds to a missing slot inside the clause, and English's silent trace is its closest parallel.
- The un-relativize test is definitive: reinsert the head into the clause with the right particle; if you get a complete sentence, it is gap type.
- The head can fill any role — subject (が), object (を), location (に／で), time (に), instrument (で) — recover the role by the particle it takes on reinsertion.
- The test cleanly separates gap-type (内の関係) from the look-alike gapless (外の関係) content modifiers, where no reinsertion is possible (魚を焼くにおい).
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Start learning Japanese→Related Topics
- Relative Clauses (連体修飾): No Relative PronounN4 — Japanese has no relative pronoun — no 'that', 'which', or 'who'; to modify a noun with a whole clause you simply place a plain-form clause directly in front of it, exactly the way an adjective sits in front of a noun.
- Gapless Modifying Clauses (外の関係)N2 — In the 'outer relation', the head noun names the content, result, or circumstance of the clause before it rather than filling a slot inside it — so 魚を焼く匂い is 'the smell of grilling fish', and 匂い is no argument of 焼く at all.
- Tense Inside Modifying ClausesN3 — The tense of a pre-nominal clause is relative to the head noun's own timeframe, not to the main verb — and inside a modifier た very often marks a resultant state (割れたコップ 'a broken cup', 曲がった道 'a winding road') rather than past time.