Nominalization: こと vs. の as Sentence-into-Noun

The choice between こと (koto) and の (no) as nominalizers comes down to one contrast: こと packages a clause as an abstract, factual proposition, while の packages it as a concrete event the speaker perceives or lives through.¹² Both turn a whole Japanese sentence into a noun. They are not freely swappable, and picking the wrong one is a classic N4–N3 slip.

Overview: two ways to make a sentence a noun

A nominalizer turns a verb, an adjective, or an entire clause into a noun-equivalent that can take particles and fill a noun slot. In this role, の "turns non-nouns (things like verbs, adjectives, or clauses) into nouns." こと, which "basically means 'thing,'" is "a versatile word for intangible, abstract things: ideas, events, experiences, and many others."³

Both nominalizers are introduced at N4.⁴⁵ Knowing each one in isolation is the easy part. The harder N4-to-N3 step is choosing between them when a sentence can take a nominalizer at all.

This article focuses on that head-to-head decision. It gives you one semantic principle, three verb-class buckets, and a register rule, so you can look at a sentence and pick.

What this article does and does not cover

This page resolves the choice between こと and の. It does not re-teach each form's full mechanics. The form-by-form attachment rules, idioms, and perception-verb lists live in the dedicated こと nominalizer article and the dedicated の nominalizer article. This page routes you there whenever you want one form in depth.

One operation is out of scope. Adjective-stem nominalization with ～さ and ～み (turning 高い into 高さ, "height") is a different process: it makes a noun out of an adjective, not out of a clause. It does not compete with こと or の and is covered in its own article.

The core principle: abstract こと vs concrete の

The choice turns on a single contrast: degree of abstraction. こと nominalizes toward an abstract, general, factual proposition; の nominalizes toward a concrete, specific, experienced event.¹²

Tofugu states it directly: "While 事 is used to talk about broad, abstract concepts, の is used to talk about more concrete actions or something familiar to you."² Put another way, の points to a specific, concrete event that has happened or may happen. こと talks about an action in the general sense, without pointing at any particular instance.²

A perspective difference sits underneath this. The two nominalizers "semantically differ largely on perceived objectivity/subjectivity": こと leans toward an objective statement treated as a distinct circumstance, while の leans toward the speaker's subjective, in-the-moment point of view.¹

The one-line test: are you reporting a fact or perceiving an event?

If the clause is a fact you know, notice, or assert from a distance, reach for こと. If it is a concrete event you are watching, hearing, or living through right now, reach for の.¹²

こと: the fact or the concept

こと nominalizes toward a proposition held at a distance: a fact the speaker knows, notices, or asserts, rather than an event being perceived in real time.¹²

見みることは信しんずることである。¹
"Seeing is believing."

That generalized, proverb-like reading is pure こと territory. It is a statement about seeing and believing in general, not a specific act of looking.

カナダが寒さむいことに気きづいた。¹
"I just noticed that Canada is cold."

彼かれが有名ゆうめいな音楽家おんがくかだということを知しりませんでした。¹
"I didn't know that he is a famous musician."

In both examples, the nominalized clause is a reportable fact: what was noticed, or what was not known. The speaker is handling a proposition, not perceiving an event, so こと fits.

の: the event you are living through

の nominalizes toward a concrete, directly perceived or directly experienced event tied to a specific situation.¹²

容疑者ようぎしゃがその部屋へやから慌あわてて出でてくるのを見みましたよ。¹
"I saw the suspect come out flustered from the room."

This is a single witnessed event, fixed in a place and time. The speaker is recounting something perceived, which is exactly the domain of の.

恋人こいびとたちは一緒いっしょにサンバを踊おどるのをやめました。¹
"The couple stopped dancing the samba together."

毎日まいにち散歩さんぽするのは健康けんこうにとてもいいようです。¹
"It seems that going for a walk every day is very good for your health."

The same contrast drives the whole article. Once you can feel "fact at a distance" versus "event up close," the verb-class rules below mostly follow from it.

Decision by verb class: which verb forces which

The semantic principle is the default. But the matrix verb, the verb whose object the nominalized clause becomes, often forces the choice outright. There are three buckets: verbs that demand の, verbs and frames that demand こと, and verbs that accept either.

Use the table as a quick lookup. The sections after it explain why each bucket behaves as it does.

Bucket	Trigger	Representative verbs / frames	Nominalizer
の-only	Reports a directly perceived or concrete ongoing event	見る, 見える, 聞く, 聞こえる, 気きがつく, 感かんじる, 待まつ, 手伝てつだう, 止とめる / やめる, 好すきだ (strong preference)	の146
こと-only	Handles the clause as an abstract proposition or a fixed expression	copula frame ...ことだ / ことです, communication / ordering / internal-thought verbs (命めいじる, 祈いのる, 約束やくそくする), set phrases ことができる / ことがある / ことにする	こと6578
Both-OK	Subject or object of an evaluation, with the abstract/concrete tilt still leaking	上手じょうずだ, 忘わすれる, 決きめる (leans こと)	either167

の-only verbs

A matrix verb forces の when it reports a directly perceived, real-time, or concrete experiential event. Perception verbs are the clearest case, and の is mandatory with them: 見る (to see), 見える (to be visible), 聞く (to hear), 聞こえる (to be audible), 気がつく (to notice), 感じる (to feel).¹⁴²

娘むすめがピアノをひいているのを見みた。⁴
"I watched my daughter play the piano."

犬いぬがしゅくだいを食たべているのが見みえる。⁴
"I saw the dog eating my homework."

The same pull applies to a small set of verbs whose action is performed on, or synchronized with, a concrete ongoing event: 止める / やめる (to stop), 待つ (to wait), 手伝う (to help), じゃまする (to interfere).⁴⁶ Stopping, waiting for, or helping with something requires that thing to be a concrete event present in the situation.

テレビゲームをするのを止やめてください。⁴
"Stop playing video games please."

ドアが開あくのを待まってください。⁴
"Please wait for the door to open."

皿さらを洗あらうのを手伝てつだいましょう。⁴
"I'll help wash the dishes."

好きだ (to like) and 嫌いだ (to dislike) also lean strongly toward の. Here の resolves a potential ambiguity. The action-liking sense uses の rather than こと, and 僕のことが好き? ("Do you like me?") shows the contrast the choice avoids.¹ In conversation, の is the natural pick.⁷

The unifying reason is simple: each of these verbs takes a concrete event happening in a specific place and time as its complement. That is exactly the domain of の.¹⁴²

Never put こと after a direct-perception verb

見る, 見える, 聞く, 聞こえる, and 感じる report a concrete, real-time event, so they take の. Using こと after them is the most common nominalizer error.⁴

こと-only verbs and frames

こと is required wherever the clause is handled as an abstract proposition, a generalized activity, or a conventionalized fixed expression. の cannot substitute in any of these.

The first こと-only context is the copula frame. A nominalized clause serving as the predicate of an identity sentence takes こと, giving clause + ことだ / ことです. の cannot stand directly before だ / です in this role; as one source puts it plainly, "の cannot be with です."⁷ The hobby pattern 趣味は...ことです is the everyday example.⁵⁷

私わたしの趣味しゅみは料理りょうりを作つくることです。⁵
"My hobby is cooking."

The second こと-only context is the fixed potential expression ことができる, the standard way to say "can do." こと is locked in because the phrase expresses generalized ability, not a concrete action: "事 here, when talking about your generalized ability to sing in Japanese, cannot be replaced with the nominalizer の because it is used for concrete actions, not general activities."²⁸ This is the clearest case where の is outright ungrammatical.

日本語にほんごで歌うたう事ことができます。²
"I can sing in Japanese."

私わたしは日本語にほんごを話はなすことができます。⁸
"I can speak Japanese."

The third こと-only context is reporting. Communication, ordering, and internal-thought verbs treat their clause as an abstract proposition, so they take こと.⁶ This bucket includes 命じる ("to order"), 祈る ("to pray"), and 約束する ("to promise"). These verbs report or assert a proposition rather than perceive an event. For their full patterns, see the reported-speech and quotation with と articles.

新鮮しんせんな息いきを吸すうことは素晴すばらしい。¹
"Breathing fresh air is wonderful."

Several こと-only set phrases beyond ことができる behave the same way: ことがある ("there are times when / have done before") and ことにする / ことになる ("decide to / it is decided that"), along with ことだ used as advice ("you should ..."). Each is a fixed, conventionalized expression that reinforces the こと-only bucket, and each has its own dedicated article. Learn them as units rather than re-deriving them here.²⁵⁸

The unifying reason mirrors the previous section: each context describes or asserts a fact rather than perceiving an event. That is exactly the domain of こと.¹²⁷

Both-OK verbs (and the nuance that still leaks)

In many basic sentences, especially where the nominalized phrase is the subject or object of an evaluation, こと and の are interchangeable: the same sentence accepts either.⁶ Subjective-comment frames such as ...のは / ...ことは followed by an adjective of evaluation (好きだ "like," 難しい "difficult," 上手だ "skilled," 下手だ "unskilled") take both. の is the natural conversational choice when the speaker has a concrete activity in mind.¹⁷

ブログを読よむのが好すきです。⁴
"I like reading blogs."

The source presents this as ブログを読む（こと・の）が好きです: either nominalizer is grammatical, with の the natural conversational pick.⁴

The nominalized clause can also be the subject or object of a verb like 忘れる (to forget), and a single sentence can stack both forms without friction.

歌うたうことは諦あきらめていただけに偶然ぐうぜん初舞台はつぶたいを踏ふめたことはとても嬉うれしかったです。¹
"Since I had given up singing, being able to debut by chance was very delightful."

"Interchangeable" is not "identical." Even where both are grammatical, the こと version reads more general and detached, while the の version reads more concrete and personal. The same hobby sentence with こと "sounds more rigid," while the version with の "sounds quite casual."² The choice is rarely truly free.

決める ("to decide") sits in this bucket but leans こと, and it connects to the ことにする / ことになる family. That decision frame is covered in its own article rather than expanded here.⁵

こと vs の decision tree

When verb class does not force the answer outright, work from the top down. Check for a fixed expression first, then ask whether you are perceiving a concrete event or reporting an abstract fact.

Register: written-formal こと vs colloquial の

Verb class is the first decision axis. Register is the second. こと is more formal and abstract, while の is more conversational and personal.²⁷ When verb class leaves the choice open, formal or written contexts pull toward こと, and spoken or casual contexts pull toward の.²⁷

This has a concrete cost in speech. Putting こと in front of a particle in everyday conversation can sound "too formal and unnatural," "like a textbook speech." 外食をすることが好きです reads stiff next to the natural 外食をするのが好きです.⁷

The pull runs the other way in formal settings. ～ことができる is "generally more appropriate in a formal setting, such as a job interview, or when objectively describing someone else's abilities." Its detached, generalized tone is the right fit there.²

Good to know

"の = now / observe, こと = concept"

Use this retention hook for the core principle: の attaches to concrete, observed, in-the-moment events (perception, real-time experience), while こと attaches to abstract concepts, general facts, and reportable propositions. The rhyme is editorial, but the distinction it encodes is the sourced abstract/concrete principle that drives every decision above.¹²

Set phrases are memorized whole, not derived

ことができる, ことがある, ことにする / ことになる, and ことだ-as-advice are fixed expressions where こと is locked in and の cannot substitute. Store them as single units rather than re-running the abstract/concrete decision each time you use one.²⁵⁸

のだ / んだ is a different の, not this nominalizer

Explanatory-の, the のだ / んだ that means "the situation is that ...," is a separate sentence-final construction. It is not the clause-into-noun nominalizer compared here. Do not conflate them. The nominalizer-の under discussion is the one that cannot precede the copula in the identity frame. Explanatory-のだ is its own topic with its own article.⁷

Using の directly before だ / です in the nominalizing role

A nominalized clause that serves as the predicate of an identity sentence takes こと, not の, because "の cannot be with です" in this role.⁷ Writing 趣味はサッカーをするのです for "my hobby is playing soccer" is wrong. The identity frame needs こと.

趣味しゅみはサッカーをすることです。⁷
"My hobby is playing soccer."

Over-using こと in speech sounds stiff; over-using の in formal writing sounds casual

The two register failures mirror each other. In everyday conversation, こと in front of a particle can sound "like a textbook speech." In essays, job interviews, and objective description, こと-heavy phrasing such as ～ことができる is the expected register fit.²⁷ Match the form to the setting, not just to the grammar.

See also

• Japanese Complement Clauses with こと: The Abstract Nominalizer for Sentences-as-Nouns
• Japanese Complement Clauses with の: The Concrete Nominalizer for Perception and Feeling
• The の Particle: Possessive, Nominalizer, Attributive
• Japanese ～という (to iu): Naming, Defining, and "the Fact That"
• Japanese Subordinate Clauses: How Embedded Clauses Work (Relative, Complement, Quotation, Embedded Question)
• Adjective Stem Nominalization in Japanese: ～さ vs. ～み

References

Footnotes

1. Imabi. "Nominalizers: の, こと, & もの." https://imabi.org/nominalization/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²²

2. Tofugu. "こと (事) for Abstract Things." https://www.tofugu.com/japanese-grammar/koto/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰

3. Tofugu. "Japanese Grammar Index." https://www.tofugu.com/japanese-grammar/ ↩

4. jlptbootcamp.com. "JLPT N4 Grammar: Battle of the Nominalizers (no and koto) 1 of 2." https://jlptbootcamp.com/2011/02/jlpt-n4-grammar-nominalizer/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³

5. JLPTsensei.com. "JLPT N4 Grammar: こと (koto) Meaning - verb nominalizer." https://jlptsensei.com/learn-japanese-grammar/%E3%81%93%E3%81%A8-koto-meaning/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

6. Wasabi. "Nominalizers: こと and の." https://wasabi-jpn.com/magazine/japanese-grammar/nominalizers-koto-and-no/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

7. Japanese Ammo with Misa. "Talking About Hobbies Completely in Japanese." https://www.japaneseammo.com/talking-about-hobbies-completely-in-japanese-with-english-subs/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴

8. Imabi. "Potential II: できる." https://imabi.org/potential-ii-%E3%81%A7%E3%81%8D%E3%82%8B/ ↩ ↩² ↩³ ↩⁴ ↩⁵