Polite (Keitai) vs Plain (Jōtai) Style: Choosing by Situation [JLPT N4]
Content by NTJ Kuma · Nihongo to Japan editorial team · Updated July 27, 2026
です・ます for formal settings, plain だ for intimates — and hold one style throughout.
「です・ます」「だ」「である」 — three writing styles, each for a setting
The same “I'm busy today” can be written 「今日は忙しいです」 (polite style), 「今日は忙しい」 (plain だ style), or the essay's 「〜である」 — Japanese has several styles, chosen by audience, setting, and text type: polite (です・ます) = courteous, formal; plain (だ style) = close, diaries; である style = essays, argumentation. The wrong style or mixing them is jarring. This guide covers the three styles' roles and setting-based choice, complementing the conversational polite/plain (its own guide).
Core: pick the style by setting／text type
Japanese has three main styles:
- Polite (です・ます) = courteous, formal: letters, outward documents, seniors, first meetings.
- Plain (だ style) = close, casual: diaries, novels, friends, social media.
- である style = objective, argumentative: papers, reports, critiques (the written formal version of 〜である・〜だ).
Key: keep one style throughout a text — don't mix polite and plain.
Styles compared
| Style | Ending | Setting |
|---|---|---|
| polite | です・ます | letters, outward, seniors |
| plain (だ style) | だ・dictionary | diaries, novels, friends |
| である style | である | papers, reports, critiques |
Examples in context
- (first business meeting) はじめまして、田中と申します。(Nice to meet you, I'm Tanaka.) — polite
- (diary) 今日はいい天気だった。(The weather was nice today.) — plain
- (paper) この結果は重要である。(This result is significant.) — である style
- (a text to a friend) 今どこにいる？(Where are you now?) — plain
- (report) 調査を実施した。〜が判明した。(A survey was conducted; ~ was found.) — だ style (report)
⚠️ Easy traps to avoid
① Keep one style within a text. In one piece or conversation, all polite or all plain — don't mix (✗ 今日は忙しいです。でも楽しかった。 — one です, one plain, jarring).
② Papers use 「である style」, not 「です・ます」. Academic papers and formal reports end in 「〜である・〜だ」 (この問題は重要である); 「です・ます」 sounds not-formal-enough, like a school essay.
③ Outward／to seniors, use polite. When unsure, default to polite (です・ます) for outward or senior audiences — same as the conversational “when unsure, polite” rule (polite/plain has its own guide).
🔄 Compare with similar forms: polite／plain／である style
| Style | Nuance | Setting |
|---|---|---|
| polite (です・ます) | courteous, formal, to people | letters, outward |
| plain (だ style) | close, casual | diaries, friends |
| である style | objective, argumentative | papers, reports |
💡 The key point in use
Style is a Japanese text's “uniform” — wear the right one for the occasion. Remember the three roles: polite (です・ます) to people, courteous (letters, outward); plain (だ style) close, casual (diaries, friends, novels); である style objective, argumentative (papers, reports). The key rule: keep one style throughout a text — don't hop between polite and plain. Practical note: write papers and formal reports in 「である style」 (〜である), not 「です・ます」 (which reads like a grade-school essay). For switching polite/plain in conversation, see the 〈polite vs plain〉 guide.
❓ Questions you might have
Q: Which style for papers and reports?
Use 「である style」 (〜である・〜だ) — the academic/formal written style (この研究は重要である, 結果は明らかだ). Don't write papers in 「です・ます」 — it sounds not-formal-enough, like an essay. Diaries and novels use 「だ style」 (dictionary-form endings); である style is the more formal, objective written version of だ style, reserved for argumentation and research.
Q: Can I mix styles?
No — keep one throughout a text. A piece stays in one style start to finish: all 「です・ます」, all 「だ・dictionary」, or all 「である」. Mixing (one です, one だ) reads as unprofessional and jarring. Decide the style before writing, then keep it consistent. (For switching polite/plain in conversation, see the 〈polite vs plain〉 guide.)
🖊️ Practice Quiz
Q1. Which register should be used in a first-meeting business scene?
(A) plain (だ/plain form)
(B) polite (ます・です)
(C) either is the same
(D) only the sentence-end need be polite
Q2. What's a natural register for a LINE message to a friend?
(A) polite (ます・です)
(B) plain (plain form/だ)
(C) either is fine
(D) must be polite
Q3. 「今日は学校に行き___。先生に褒め___。」(a formal diary, consistently polite)
(A) た、られた (B) ました、られました (C) た、られました (mixed → wrong) (D) both A and B
Q4. Which is correct as a paper's sentence-ending?
(A) 〜だと思います。(ます → colloquial)
(B) 〜であると考えられる。(plain, academic written style)
(C) 〜だよ。(colloquial, informal)
(D) 〜ですかね。(too soft)
Q5. What happens if you mix the polite and plain registers?
(A) it sounds more natural
(B) it sounds unnatural (the style consistency breaks)
(C) it's recommended in papers
(D) you can speak faster
Answer Key
1. (B) polite (ます・です) ── a first-meeting business scene is the most formal → always use the polite register. Plain is only for intimate relationships.
2. (B) plain (plain form/だ) ── a LINE message to a friend naturally uses the plain register.
3. (B) ました、られました ── a formal diary keeps the register consistent (polite throughout); mixing is wrong.
4. (B) 〜であると考えられる ── papers use the plain, academic written style.
5. (B) ── mixing registers sounds unnatural (it breaks the style consistency).