The Difference Between 「うん」と「はい」の使う相手の違いの違い｜Japanese Grammar (N5–N3)

(Joy standing straight and saying Hai to a boss [Formal] vs. Ken relaxing and saying Un to a friend [Casual])

“Did you understand?” -> Hai, wakarimashita. (Formal) “Did you understand?” -> Un, wakatta. (Casual) In English, we can comfortably say “Yes” or “Yeah” depending on our mood. In Japanese, however, your choice between はい (Hai) and うん (Un) has nothing to do with your mood—it is entirely based on who you are talking to. Mixing them up can make you sound incredibly rude, or awkwardly distant. Let’s look at what happens when Joy accidentally uses the wrong word at work.

🗣 Conversation Scene

Joy is listening to instructions from her older manager, Tanaka-san.

Tanaka

Joyさん、このデータを明日までにエクセルに入力しておいてください。 (Joy, please enter this data into Excel by tomorrow.)

Joy

うん、わかりました！ (“Un” [Yeah], I understood!)

[ Tanaka-san looks slightly annoyed. Ken quickly whispers to Joy. ]

Ken

Joyさん！会社で上司に「うん」は絶対にダメです！すごく失礼ですよ。「はい」と言ってください。 (Joy! You absolutely cannot say “Un” to a boss at work! It is very rude. Please say “Hai”.)

💡 Explanation

Social Distance vs. Intimacy

⚠️ The Golden Rule of Yes: If you must use polite Japanese (Desu/Masu) with someone, you must use “Hai.” If you are allowed to use casual Japanese (Short Form) with someone, you can use “Un.”

1. はい (Hai) = Formal Yes 👔

Target Audience: Superiors, Strangers, Customers, Teachers. “Hai” creates a respectful, polite boundary between you and the listener. It acknowledges that there is a professional or social distance. In business, it shows that you are an alert, responsible adult.

[To a boss] はい、すぐやります。 (Yes, I will do it immediately.)
[To a store clerk] はい、お願いします。 (Yes, please. *Maintaining polite distance*)

2. うん (Un) = Casual Yeah 👟

Target Audience: Close friends, Family, Juniors (younger people). “Un” removes the social boundary. It shows intimacy, warmth, and closeness. It is often accompanied by a relaxed nod. You only use “Un” with people who are inside your “inner circle.”

[To your mom] うん、美味しかったよ。 (Yeah, it was delicious.)
[To a best friend] うん、一緒に行こう！ (Yeah, let’s go together!)

📊 Comparison Table

Word	Who to use it with	Impression / Nuance
はい (Hai)	Bosses, seniors, teachers, strangers.	Professional & Respectful. Maintains a polite wall.
うん (Un)	Family, close friends, younger siblings.	Intimate & Relaxed. Shows you are close.

🚧 The “Childish” Trap

Because children naturally say “Un” to their parents, using “Un” with an older person or a boss in Japan makes you sound exactly like a 5-year-old child! It strips away all your professional credibility. Even if your boss is friendly and smiles a lot, you must protect your professional image by answering with a crisp “Hai.”

🔥 Practice Quiz

Tap to check the answer!

Q1. A police officer stops you to ask if you dropped a wallet. What should you say? A. Un, watashi no desu. B. Hai, watashi no desu.

Answer: B (Hai) A police officer is a stranger in an official capacity. You must use formal language (“Hai”).

Q2. You are playing video games at home. Your younger sister asks, “Is this game fun?” What should you say? A. Un, tanoshii yo! B. Hai, tanoshii desu!

Answer: A (Un) With your younger sister, using “Hai” creates an awkward, cold distance. “Un” shows warmth and family intimacy.

Keep practicing with JPLT!