Polite/Casual Switching (使い分け)
Supporting / Social Dynamics
👀 Layer A: Visual Guide (直感理解)
📝 Quick Summary (まとめ)
相手との関係によって話し方を変えるルールです。「丁寧体（です・ます）」は社会的な距離がある人へ、「普通体（タメ口）」は親しい人へ使います。
This is the social rule of switching between Polite (Desu/Masu) and Casual (Plain) speech. Use Polite for “Public/Outer” relations and Casual for “Private/Inner” relations.
Polite (Soto): 先生、ボス、知らない人 (Teachers, Boss, Strangers)
Casual (Uchi): 家族、友達 (Family, Friends)
🔍 Layer B: Deepening (深掘り)
💡 Raya’s Hack (攻略法)
迷ったら「丁寧」で！
まだ日本語に慣れていないときは、誰に対しても「丁寧体（です・ます）」を使っておけば間違いありません。
友達に丁寧すぎるのは少し変ですが、目上の人にタメ口を使うのは「失礼」になります。
安全策（Safety First）でいきましょう！
When in doubt, use Polite Form. It’s never “wrong” to be polite. Being too polite to a friend is just awkward, but being casual to a boss is rude. Play it safe!
🚧 Joy’s Mistake (よくある間違い)
Scene: Joy tries to be polite but mixes grammar.
Joy: 「私は 寿司を 食べる です。」
(Watashi wa sushi o taberu desu.)
❌ Grammar Clash!
Why?
動詞の辞書形（食べる）に「です」をつけてはいけません。
丁寧にするなら「ます形」にします。
× 食べるです → 〇 食べます
You cannot add “Desu” to a Plain Verb. This is a common mistake. To make a verb polite, change it to “Masu-form”. Correct: “Tabemasu”.
🔥 Layer C: Practice Loop
Now it’s time to test your learning through the next 10 practice drills!
Level 1: Who are you talking to?
Q1. Talking to your Boss
(Always polite with superiors)
Q2. Talking to your younger sister
(Family is Uchi / Inner circle)
Q3. Talking to a stranger on the street
(Strangers are Soto / Outer circle)
Q4. Talking to a close friend
(Friends are Uchi)
Q5. Talking to a shop staff
(Public interaction)
Level 2: Switch the Sentence
Q6. Polite: “Tabemasu” → Casual?
(Dictionary form)
Q7. Casual: “Ikanai” → Polite?
(Masen form)
Q8. Polite: “Mimashita” → Casual?
(Ta form)
Q9. Casual: “Isogashii” → Polite?
(Add Desu for i-adjectives)
Q10. Casual: “Gakusei” (Student) → Polite?
(Add Desu for nouns)
