Use the polite desu/masu form with anyone you don't know well: strangers, shop staff, coworkers, teachers and anyone older. Use the plain form with close friends, family and children. Full keigo, the honorific and humble verbs, sits above desu/masu, and as a beginner you mainly need to recognize it, not produce it.
English speakers make polite sentences by adding words: "could you," "would you mind," "please." Japanese builds politeness into the ending of the verb. That means a sentence can be rude even if it contains a polite word. ちょっと待って (Chotto matte), "Wait a sec," is fine with a friend and abrupt with a stranger. ちょっと待ってください (Chotto matte kudasai) is the everyday polite version, and staff in a shop will say 少々お待ちください (Shōshō omachi kudasai), which is a level higher again.
The flip side: you can't fix a plain-form sentence by smiling or adding "sorry." The register is in the grammar, so pick it before you open your mouth.
| Layer | What it does | Example |
|---|---|---|
| 丁寧語 (teineigo), polite | Makes your speech polite toward the listener | 行きます (ikimasu), I go |
| 尊敬語 (sonkeigo), honorific | Raises the person you are talking about | いらっしゃいます (irasshaimasu), they go |
| 謙譲語 (kenjōgo), humble | Lowers yourself or your group | 参ります (mairimasu), I go |
The key idea for English speakers: honorific verbs are only for other people, humble verbs are only for yourself and your side. English has nothing like this. "My boss is coming" and "I'm coming" use the same verb in English, but in formal Japanese they use different ones.
| Meaning | Plain | Polite |
|---|---|---|
| eat | 食べる (taberu) | 食べます (tabemasu) |
| don't eat | 食べない (tabenai) | 食べません (tabemasen) |
| ate | 食べた (tabeta) | 食べました (tabemashita) |
| didn't eat | 食べなかった (tabenakatta) | 食べませんでした (tabemasen deshita) |
| let's eat | 食べよう (tabeyō) | 食べましょう (tabemashō) |
| is (a student) | 学生だ (gakusei da) | 学生です (gakusei desu) |
| is expensive | 高い (takai) | 高いです (takai desu) |
Notice that i-adjectives such as 高い (takai) do not take だ (da) in the plain form. Saying 高いだ is a common learner error. In casual speech, だ is also often dropped after nouns: 学生? (Gakusei?) works as "You're a student?"
| Person | Use |
|---|---|
| Stranger on the street, station staff | desu/masu |
| Shop and restaurant staff | desu/masu (they will use full keigo with you) |
| Coworker your age, at first | desu/masu |
| Boss, client, teacher | desu/masu plus some honorific verbs |
| Your partner's parents | desu/masu |
| Close friends, siblings, children | plain form |
Age and status are not symmetrical. A senior colleague or an older neighbor may speak to you in plain form while you keep using desu/masu, and that is normal, not rude. Switching to plain form is usually offered by the higher-status or older person. You may hear タメ口でいいよ (Tameguchi de ii yo), "You can talk casually with me." タメ口 (tameguchi) is the word for casual speech between equals. With people your own age, the switch often happens naturally once you are friends.
| Plain | Honorific (for others) | Humble (for yourself) |
|---|---|---|
| いる (iru), be | いらっしゃる (irassharu) | おる (oru) |
| 行く・来る (iku, kuru), go, come | いらっしゃる (irassharu) | 参る (mairu) |
| 言う (iu), say | おっしゃる (ossharu) | 申す (mōsu) |
| 食べる (taberu), eat | 召し上がる (meshiagaru) | いただく (itadaku) |
| 見る (miru), see | ご覧になる (goran ni naru) | 拝見する (haiken suru) |
| する (suru), do | なさる (nasaru) | いたす (itasu) |
| 知っている (shitte iru), know | ご存じだ (gozonji da) | 存じている (zonjite iru) |
You already know some of these from set phrases. いらっしゃいませ (Irasshaimase), the shop greeting, comes from いらっしゃる (irassharu). いただきます (Itadakimasu), said before eating, is the humble verb for receiving. 申します (mōshimasu) shows up in introductions: スミスと申します (Sumisu to mōshimasu), "My name is Smith," a step more formal than スミスです (Sumisu desu).
Desu/masu is the right starting point because it is safe with almost everyone you will meet as a traveler or a new coworker. But plain form is not just casual speech. It is the dictionary form, and polite sentences contain plain verbs inside them: 明日行くと思います (Ashita iku to omoimasu), "I think I'll go tomorrow," has the plain 行く (iku) before と思います (to omoimasu). Relative clauses work the same way: 昨日見た映画 (kinō mita eiga), "the movie I saw yesterday." Plain style is also standard in newspapers, essays and diaries, where it carries no rudeness at all.
The fastest way to make the switch automatic is to say the same sentence both ways, once to a friend and once to a stranger, until you can feel the difference. A tutor who can play both roles helps, and so does noticing which form people use with you in a real shop or office.
Desu/masu is teineigo, the polite layer, and Japanese grammar books count it as one of the forms of keigo. In everyday conversation, though, people often use the word keigo to mean the honorific and humble verbs that sit above it.
As a learner, consistent desu/masu is enough for almost every situation, and people expect mistakes with honorific and humble verbs. The risk is the other direction: using plain form with a stranger or someone older sounds far worse than imperfect keigo.
You can, but it keeps a distance. If a friend keeps using plain form with you and you stay in desu/masu, it can feel like you are holding them at arm's length. Follow their lead.
失礼します (Shitsurei shimasu) literally means I am being rude. People say it when entering or leaving a room, especially an office, or when interrupting. 失礼しました (Shitsurei shimashita) is said on the way out.
