Japanese particles like が, を and は attach to nouns. So how do you say "I like running," where the thing you like is an action, not a thing? You turn the verb into a noun first. The particle の does exactly that: placed after a plain-form verb or a whole clause, it packages that clause into a noun phrase that can now be the subject, object, or topic of a bigger sentence. English does the same work with the -ing form ("I like running") or with "the fact that…" ("I saw that he came"). In Japanese, one small の carries the whole load.
This nominalizing の is a different animal from the possessive/appositive の you have already met, and it competes with a rival nominalizer, こと. Knowing when の is required — and when it is actually wrong — is one of the real hurdles at the N4 level. This page teaches the mechanics and the single most important rule; the full の-versus-こと decision tree lives on the koto vs no page.
The mechanics: plain form + の
To nominalize, take the clause in its plain form (dictionary form, plain past, plain negative — never the polite です/ます form) and stick の on the end. The whole thing now behaves like a noun.
- 走る (run) → 走るの (running / the running)
- 泳ぐ (swim) → 泳ぐの (swimming)
- 田中さんが来た (Tanaka came) → 田中さんが来たの (Tanaka's coming / that Tanaka came)
Once nominalized, the phrase takes whatever particle the outer sentence needs:
泳ぐのが好きで、夏はほぼ毎日プールに行く。
oyogu no ga suki de, natsu wa hobo mainichi pūru ni iku
I love swimming, so in summer I go to the pool almost every day.
走るのは楽しいけど、朝早く起きるのがつらい。
hashiru no wa tanoshii kedo, asa hayaku okiru no ga tsurai
Running is fun, but getting up early is the hard part.
Here 泳ぐの and 走るの are subjects (marked が / は), and 好き and 楽しい comment on them. Without の, the verb would have nothing for が or は to grab onto.
Nominalizing a full clause, subject and all
の doesn't just nominalize a lone verb — it can wrap an entire clause, complete with its own subject and object. The embedded clause keeps its internal が and を; の simply turns the finished clause into a noun.
日本語を話すのは難しいと思っていたけど、慣れてきた。
nihongo o hanasu no wa muzukashii to omotte ita kedo, narete kita
I thought speaking Japanese would be hard, but I'm getting used to it.
田中さんが会場に入ってくるのを見た。
Tanaka-san ga kaijō ni haitte kuru no o mita
I saw Tanaka come into the venue.
In the second sentence, the whole event Tanaka enters the venue (田中さんが会場に入ってくる) becomes the object of 見た via のを. A useful side note: the subject inside such a clause may swap its が for の (彼が歌うの = 彼の歌うの), because you are now inside a modifying structure — that が/の interchange has its own page.
The rule that trips everyone up: perception and waiting take の
Here is the one you must not get wrong. Verbs of direct perception and of waiting take の, not こと. These include 見る (see), 見える／見かける, 聞く (hear), 聞こえる, 感じる (feel), 待つ (wait for), and 手伝う／止める (help / stop someone doing something). The logic is concrete: with these verbs you are perceiving or experiencing an actual, unfolding event in front of you — not entertaining an abstract idea about it.
彼が歌うのを初めて聞いて、びっくりした。
kare ga utau no o hajimete kiite, bikkuri shita
I heard him sing for the first time and was amazed.
誰かが泣いているのが聞こえる。
dareka ga naite iru no ga kikoeru
I can hear someone crying.
バスが来るのをもう三十分も待っている。
basu ga kuru no o mō sanjuppun mo matte iru
I've been waiting for the bus to come for a full thirty minutes.
Swap in こと and the meaning changes or breaks. 彼が歌うのを聞いた means "I heard him sing (I was there, my ears caught the singing)." But 彼が歌うことを聞いた means "I heard that he sings (someone told me the fact)." The first is perception; the second is secondhand report. For live, in-the-moment perception, only の works.
の vs こと, in one paragraph
The broad division: の nominalizes for the concrete, experienced, or perceived — events you see, hear, wait for, enjoy, or watch happen. こと nominalizes for the abstract — facts, definitions, rules, decisions, and things you say, think, decide, or pray for. So a hobby (an abstract category of activity) is stated with こと: 趣味は古い映画を見ることです. And certain fixed grammar patterns lock in こと and refuse の — most importantly …ことができる (ability) and …ことにする／…ことになる (deciding / being decided).
趣味は古い映画を見ることです。
shumi wa furui eiga o miru koto desu
My hobby is watching old movies.
一人で富士山に登ることができた。
hitori de Fujisan ni noboru koto ga dekita
I was able to climb Mt. Fuji by myself.
This is only the headline; many verbs accept either with a shift in nuance, and some genuinely allow both. Work carefully through the full contrast on the koto vs no page.
Don't confuse it with the explanatory の (のだ／んだ)
One more の to keep in its own box. The nominalizer の (走るのが好き) is not the explanatory の of のだ／んだ (走るんだ = "the thing is, I run / it's that I run"). They look identical after a plain verb, and context tells them apart: if の is followed by が／を／は and functions as a noun, it's the nominalizer; if it is followed by だ／です (or ん just runs into だ) and colors the tone of the whole statement, it's the explanatory の. See のだ / んだ for that use.
Also distinct is the "one" の — the pronoun-like の that stands in for an already-known noun: 赤いのが欲しい ("I want the red one"), 大きいのをください ("the big one, please"). That の replaces a noun; the nominalizer の replaces nothing — it converts a clause into a noun.
Common Mistakes
1. Using こと for something you perceived. Perception verbs demand の.
❌ 彼が歌うことを聞いた。
Wrong for 'I heard him singing' — this means 'I heard THAT he sings' (a report).
✅ 彼が歌うのを聞いた。
kare ga utau no o kiita
I heard him sing (I was there).
2. Omitting the nominalizer entirely. You cannot hang が or は straight onto a verb.
❌ 走るが好きだ。
Incorrect — が can't attach to a bare verb.
✅ 走るのが好きだ。
hashiru no ga suki da
I like running.
3. Dropping の before は on a clause subject.
❌ 日本語を話すは難しい。
Incorrect — the clause must be nominalized first.
✅ 日本語を話すのは難しい。
nihongo o hanasu no wa muzukashii
Speaking Japanese is hard.
4. Using の in a fixed こと pattern. Ability and decision patterns are locked to こと.
❌ 泳ぐのができる。
Incorrect — the ability pattern is ...ことができる.
✅ 泳ぐことができる。
oyogu koto ga dekiru
I can swim.
5. Adding politeness inside the clause. Nominalize the plain form, not the polite form.
❌ 走りますのが好きです。
Incorrect — the inner verb must be plain (走る).
✅ 走るのが好きです。
hashiru no ga suki desu
I like running. (polite)
Key takeaways
- の after a plain-form clause turns it into a noun, so it can take が / を / は.
- The embedded clause keeps its own が / を; の wraps the whole thing.
- Perception and waiting verbs (見る・聞く・感じる・待つ) take の, never こと — you perceive live events.
- Broadly: の = concrete/experienced/perceived; こと = abstract facts, definitions, decisions.
- Fixed patterns ことができる and ことにする／ことになる reject の.
- Keep the nominalizer の separate from the explanatory のだ／んだ and from the "one" の (赤いの).
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Start learning Japanese→Related Topics
- のだ / んです: The Explanatory MoodN4 — One of Japanese's highest-frequency structures — のだ／んです frames a statement as an explanation, reason, or account of the situation rather than a bare fact.
- こと vs の: Choosing a NominalizerN2 — The pocket decision card for the two nominalizers: see-or-hear it ⇒ の, fixed pattern or 'X is Y' predicate ⇒ こと, otherwise free — with の in speech, こと in writing.
- の: Apposition and Compound ModifiersN4 — How の links two nouns that name the same thing (友達の田中さん) and stands in for an English adjective (緑の車, 本当のこと), and how to tell apposition apart from possession.
- の Replacing が in Modifying ClausesN4 — Inside a noun-modifying (relative) clause, the subject が can be swapped for の — 私が作ったケーキ = 私の作ったケーキ, 髪の長い人 — and why that の is a signal you're inside a modifier.
- Turning Clauses into Noun PhrasesN4 — Japanese has no infinitive or gerund, so any verb phrase you want to use as a noun — subject, object, or topic — must be overtly nominalized with こと or の (or 〜ということ for a proposition): 泳ぐのが好きだ, 本を読むことが大切だ.
- の: The Concrete NominalizerN4 — の turns a clause into a concrete, witnessed event — which is why it is required after perception verbs like 見る and 聞こえる: you can literally see or hear the の-clause happen.