Turning Verbs into Nouns in Japanese: Koto and No

Why nominalisation is the gateway to adult sentences

Beginner sentences have nouns in the slots: Japanese is fun, I like films. Adult sentences put whole actions in those slots: speaking Japanese is fun, I like watching films with friends, I forgot to lock the door. English does this with -ing or with to, and Japanese does it by putting koto or no after a clause so that the clause behaves like a noun and can take wa, ga, or o. Until you can do this, every opinion, hobby, ability, and experience has to be squeezed into a short, childish shape.

The machinery is small. There is one forming rule, a short list of patterns that fix the choice, and one rule of thumb for everything else. The examples below start with the beginner sentence and then show the adult version, so you can hear what the nominaliser adds.

How to turn a clause into a noun

Put the clause in plain form, then add koto or no. Plain form means the dictionary form, the nai form, the ta form, or the nakatta form, so hanasu koto, hanasanai koto, hanashita koto, and hanasanakatta koto are all available. Politeness is never added inside the clause; it goes on the final verb of the whole sentence. The commonest learner error is hanashimasu koto, which sounds like two sentences glued together. Say the plain clause, then the nominaliser, then carry on with the particle and the rest.

Adjectives and nouns work too. An i-adjective attaches directly: takai no, samui koto. A na-adjective needs na before either nominaliser: shizuka na no, benri na koto. Inside the clause, the subject usually takes ga rather than wa, because wa marks the topic of the whole sentence and the nominalised clause is only a part of it: tomodachi ga kuru no o matte imasu, I am waiting for my friend to come.

No for what you experience, koto for what you think about

When neither pattern forces the choice, ask how close the action is to the speaker. No points at something concrete and present: an event you watched, a feeling you have right now, an activity you do and enjoy. Koto steps back and treats the action as a general idea: a principle, a duty, a fact about the world. That is why no dominates casual conversation and koto dominates essays, announcements, and careful speech. With suki, kirai, jōzu, and nigate, both are correct, and no is simply the one you will hear more often from a friend.

A second consequence is that koto sounds more considered. Oyogu no ga suki desu says you like swimming as an experience; oyogu koto ga suki desu says the same thing a shade more formally, as if answering a form. Neither is wrong. What is wrong is treating the two as always interchangeable and then colliding with one of the fixed patterns in the next section.

Which nominaliser each pattern requires

The logic behind the two blocks is consistent. Verbs of perceiving, waiting, helping, and stopping act on an event that is happening in front of you, so they take no. Patterns about ability, experience, decisions, arrangements, and reported content treat the action as an idea, so they take koto. Learn the table as two families rather than fifteen separate facts.

Koto ga aru: past experience versus something that sometimes happens

This pattern changes meaning with the tense of the verb before it, and both meanings are common in conversation. With the ta form, koto ga aru reports a life experience, the equivalent of English have ever: itta koto ga arimasu, I have been. With the dictionary form, it reports something that happens occasionally: iku koto ga arimasu, I sometimes go. The question form ta koto ga arimasu ka is one of the most useful small-talk tools in the language, and the answers are simply arimasu or arimasen.

Two cautions. Ta koto ga aru is about experience across your life, not about a recent event, so for last week's trip say senshū Nihon ni ikimashita, not itta koto ga arimasu. And the verb before koto must be plain: ikimashita koto ga arimasu is a common error that marks a learner immediately.

Koto ga dekiru, koto ni suru, and koto ni naru

Three further patterns are welded to koto. Koto ga dekiru expresses ability and possibility; it is longer than the potential form and sounds a little more careful, which suits suru verbs and polite questions about what is allowed. Koto ni suru marks a decision you made yourself: hashiru koto ni shimashita, I have decided to run. Koto ni naru marks an outcome decided by circumstances or by other people, and Japanese speakers also use it modestly for their own big news, so a wedding or a new job is often reported with koto ni narimashita even when the speaker chose it.

Koto desu at the end of a sentence belongs to the same family and is worth a separate note. Shumi wa shashin o toru koto desu, my hobby is taking photos, must use koto, because shashin o toru no desu would be heard as the explanatory ending covered below and would mean something like the thing is, I take photos.

The perception verbs and waiting verbs that take no

Miru, mieru, kiku, kikoeru, and kanjiru take an event you perceive directly, and that event is always nominalised with no. The same holds for matsu, tetsudau, and tomeru, which act on something in progress in front of you. Inside the clause the person doing the action takes ga, so the shape is person ga action no o verb. Learners reach for koto here because it feels safer; in these slots it is wrong, or, with kiku, it flips the meaning to hearsay.

No da and n desu: the ending you hear constantly

The no in n desu is the same nominaliser. The whole sentence is turned into a noun and then desu is added, so the literal meaning is it is that, or the situation is that. In speech no desu contracts to n desu, and in plain style it is no da or n da, both casual. Speakers use it to give background, to explain a reason, to ask for one, and to soften a statement into shared understanding. That is why you hear it constantly: dō shita n desu ka, what is the matter; atama ga itai n desu, the thing is, my head hurts.

The learner error runs in both directions. Leaving it out makes a reason sound like a bald announcement: densha ga tomarimashita is a fact, while densha ga tomatta n desu is an apology with a reason. Putting it in everywhere is the opposite problem, because watashi wa gakusei na n desu in a self-introduction sounds as if you are justifying something. Use n desu when the listener can hear a why behind it.

Notice that na-adjectives and nouns take na before n desu, exactly as they take na before the nominaliser no in the forming section. It is the same grammar seen twice, which is a good reason to learn n desu as a nominaliser rather than as a mysterious sentence ending.

Mono: the third nominaliser in fixed expressions

Mono, which literally means thing, nominalises in a handful of set patterns, and each carries an attitude that koto and no do not. Verb plus mono desu states how things generally are, often with a note of resignation or of teaching. Ta form plus mono desu looks back on what you used to do, with nostalgia. Mono desu kara gives a reason apologetically. Mono de wa arimasen says that something is simply not done. Learn these four shapes as chunks and recognise them when a Japanese speaker uses them.

Minimal pairs where the choice changes the meaning

Here only the nominaliser changes. Read each pair aloud and say the English before you check it. The kiku pair is the most important: with no you heard the singing with your own ears, with koto you were told about it. The koto desu and n desu pair shows why a hobby sentence cannot end in no desu. The final pair contrasts an experience with a habit using koto ga aru.

Kare ga kuru koto o machimashita is not a sentence a native speaker would produce, and kare ga kuru no o tsutaemashita is equally odd, because waiting is done in front of an event and passing on news is done with a piece of information. Once you feel that difference, the rest of the table follows from it.

How to make the choice automatic

• Say the plain clause first, then add the nominaliser, then the particle: hanasu, hanasu koto, hanasu koto ga dekimasu.
• Learn the koto family as one chant: koto ga dekiru, koto ga aru, koto ni suru, koto ni naru, koto desu.
• Learn the no family as verbs you do with your senses and hands: miru, kiku, kanjiru, matsu, tetsudau, tomeru.
• For everything else, default to no in conversation and koto when you would write it down.
• Ask one ta koto ga arimasu ka question in every practice session and answer it about yourself.
• When you give a reason for being late or saying no, end it with n desu and listen for how much softer it sounds.