hairu-vs-hairou

入る (hairu) and 入ろう (hairou) look nearly identical — they are even written with the same kanji. But they serve completely different grammatical functions. 入る is the plain form verb meaning “to enter.” 入ろう is the volitional form, meaning “Let’s go in!” or “I’ll go in.” Getting this wrong can lead to sentences that do not make sense — or sound like you are talking to yourself when you mean to invite someone. Here is everything you need to know.

Yuka

Hey Rei! I keep mixing up 入る and 入ろう. Can you break it down for me?

Rei

Sure! They’re both useful words but used in different situations. Let me walk you through it with some examples!

At a Glance: 入る vs. 入ろう

入る (hairu) — To Enter, To Go Into

入る is a う-verb (godan verb) meaning “to enter” or “to go into.” It is the plain dictionary form — used in statements, questions, negative forms, and as a modifier before nouns. It describes the act of entering a place or being included in something.

Note: 入る has two possible readings depending on context. は-い-る (hairu) means “to enter” (physical movement into a space). い-れ-る (ireru) means “to put something in.” They look similar but are different verbs — see our related article on 入る vs. 入れる for details.

Example 1 — entering a place:

この建物に入るには許可が必要です。
Kono tatemono ni hairu ni wa kyoka ga hitsuyou desu.
Permission is required to enter this building.

Example 2 — joining a club or group:

来年、テニス部に入るつもりです。
Rainen, tenisu-bu ni hairu tsumori desu.
I plan to join the tennis club next year.

Example 3 — describing a state or fitting inside:

この荷物はトランクに入らない。
Kono nimotsu wa toranku ni hairanai.
This luggage doesn’t fit in the trunk.

Yuka

Oh, so 入る is used that way! I never thought about it like that.

Rei

Exactly! Once you see it in context a few times, it starts to feel natural. The key is paying attention to 入る when you read or listen.

入ろう (hairou) — Let’s Go In / I’ll Go In

入ろう is the volitional form (意向形, ikoukei) of 入る. The volitional form expresses one of two things: a suggestion or invitation (“Let’s ~”) or a first-person intention (“I’ll ~” / “I’m going to ~”). It is one of the most important verb forms for natural conversation.

Formation note: For う-verbs, the volitional is formed by changing the final -u sound to -ou. 入る (hairu) → 入ろう (hairou). For polite speech, use 入りましょう (hairimashou).

Example 1 — suggestion (Let’s go in):

寒いね。中に入ろう。
Samui ne. Naka ni hairou.
It’s cold, isn’t it? Let’s go inside.

Example 2 — personal intention:

今夜は早くお風呂に入ろう。
Konya wa hayaku ofuro ni hairou.
I’ll take a bath early tonight.

Example 3 — polite suggestion:

そろそろ中に入りましょうか。
Sorosoro naka ni hairimashou ka.
Shall we go inside soon?

Yuka

And what about 入ろう? I always thought it was the same as 入る…

Rei

Easy mistake! 入ろう has its own distinct meaning. The difference becomes really clear once you compare them side by side — which is exactly what we’re doing here!

Volitional Form: A Quick Reference

The volitional form is used in three main ways:

Side-by-Side Comparison

Decision Flowchart: 入る or 入ろう?

You want to use the verb 入る (hairu) in a sentence.
        |
        v
Are you making a SUGGESTION or stating YOUR INTENTION
to enter something ("let's go in" / "I'll go in")?
   |           |
  YES          NO
   |           |
   v           v
入ろう          Are you describing entering as a FACT,
(Volitional:    asking a question, or using it as a modifier?
Let's go in /      |           |
I'll go in)       YES          NO
                   |            |
                   v            v
               入る (hairu)   Check your context
               (Plain form:   — another verb form
               enter / goes  may be needed
               in / entered)

Quick Quiz — Test Yourself!

Yuka

Okay, I feel a lot more confident about 入る and 入ろう now! Should we test it with a quiz?

Rei

Let’s do it! A quick quiz is the best way to make sure the difference really sticks.

Choose 入る or 入ろう for each sentence.

Q1. Let’s go into that bookstore over there.
あの本屋に＿＿＿よ。
Ano hon’ya ni ___ yo.

Answer: 入ろう (hairou)
Reason: This is a suggestion to go in together — use the volitional form.

Q2. You need a ticket to enter this museum.
この美術館に＿＿＿にはチケットが必要です。
Kono bijutsukan ni ___ ni wa chiketto ga hitsuyou desu.

Answer: 入る (hairu)
Reason: This is a factual statement about entry requirements — plain form.

Q3. I’m going to take a bath now.
今からお風呂に＿＿＿。
Ima kara ofuro ni ___.

Answer: 入ろう (hairou)
Reason: First-person intention — volitional form.

Q4. The water doesn’t fit in this bottle.
水がこのボトルに＿＿＿ない。
Mizu ga kono botoru ni ___ nai.

Answer: 入ら (haira) — 入らない (hairanai)
Reason: This is a factual negative statement. The plain form 入る is conjugated to the negative 入らない.

Q5. Shall we go in now? (polite)
そろそろ中に＿＿＿か。
Sorosoro naka ni ___ ka.

Answer: 入りましょう (hairimashou) — 入りましょうか
Reason: Polite volitional form + か = polite “Shall we?” suggestion.

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あわせて読みたい

Dive deeper into the verb 入る with our guide on 入る vs. 入れる — entering vs. putting something in:

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Also check out our guide on いる vs. 入る — two verbs with the same kanji that trip up beginners:

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