Japanese Polite Form: desu, masu, mashou, masen ka

Japanese has two full registers of speech, and every sentence you will ever say exists in both. The polite one — the one every textbook starts you on — is built from two endings: です (desu) for nouns and adjectives, and ます (masu) for verbs. Leaving ます off a verb is not a small mistake; it is the difference between talking to your friend and talking to your boss's client.

This page covers the whole polite register: how to form it, how to make it past and negative, how to use it to suggest and to invite, and — just as important — when a Japanese speaker would drop it.

What the two endings do

• です (desu) attaches to nouns and adjectives: 学生です (gakusei desu, "I'm a student"), 高いです (takai desu, "it's expensive").
• ます (masu) attaches to a verb stem: 行きます (ikimasu, "I go / I will go"), 食べます (tabemasu, "I eat / I will eat").

A dictionary-form verb spoken to a stranger sounds abrupt, almost like an order. 行く (iku, "go") is what you say to a friend; 行きます (ikimasu) is what you say to anyone you have just met. The verb itself carries no politeness — the ending does.

The polite forms in one table

Two things to notice immediately. First, the negative is a different word, not a different ending: です (desu) has no negative of its own, so the sentence switches to じゃない (ja nai) or じゃありません (ja arimasen) and keeps です (desu) only to stay polite. Second, past tense lives on the ending: ました (mashita) for verbs, でした (deshita) for nouns.

Adjectives behave like nouns here

い-adjectives need no です (desu) change at all — the adjective inflects itself:

な-adjectives and nouns follow the same pattern as each other: 静かです (shizuka desu, "is quiet"), 静かじゃないです (shizuka ja nai desu, "is not quiet"), 静かでした (shizuka deshita, "was quiet").

Suggesting with ましょう (mashou)

ましょう (mashou) is the ます (masu) stem plus しょう (shou). It means "let's" or "I'll do it for you" — and crucially, it is not a question. You use it when the decision is already effectively made.

• 一緒に行きましょう (issho ni ikimashou, "let's go together")
• 手伝いましょう (tetsudaimashou, "I'll help you")
• そろそろ始めましょう (sorosoro hajimemashou, "let's get started")

If a colleague says お腹すいた (onaka suita, "I'm hungry"), replying ご飯を食べに行きましょう (gohan o tabe ni ikimashou, "let's go get food") is natural — you are moving the group, not asking permission.

ましょうか (mashou ka) softens it into an offer that checks with the other person first: 窓を開けましょうか (mado o akemashou ka, "shall I open the window?"), 一緒にやりましょうか (issho ni yarimashou ka, "shall we do it together?").

Inviting with ませんか (masen ka)

ませんか (masen ka) is the negative question form, and it is the single most useful invitation pattern in the language. Literally "won't you do…?", it hands the decision to the other person:

• コーヒーでも飲みませんか (koohii demo nomimasen ka, "won't you have a coffee with me?")
• 週末、買い物に行きませんか (shuumatsu, kaimono ni ikimasen ka, "would you like to go shopping this weekend?")

ませんか (masen ka) is politer than ましょう (mashou) and works upward — a subordinate can invite a manager with it. That is exactly why it is the safe choice when you are not sure of your standing. Compare the same event said two ways:

Answering an invitation

• Accept: いいですね (ii desu ne, "that sounds good"), そうしましょう (sou shimashou, "let's do that"), ええ、行きましょう (ee, ikimashou, "yes, let's go").
• Decline softly: すみません、ちょっと… (sumimasen, chotto…, "sorry, that's a bit…") — leaving the sentence unfinished is the polite refusal. また今度 (mata kondo, "next time") also works.

Japanese refusals rarely say no directly. A trailing ちょっと (chotto, "a little…") is understood as a no, and pressing after hearing it is the rude move.

Plain form is not "casual polite" — it is a different register

Plain form is what anime, drama, diaries and internal monologue run on. It is not rude in itself; it is the register you use with people you are close to. But it is also the form that goes inside most complex grammar: と思う (to omou, "I think"), と言った (to itta, "said that"), から (kara, "because") all connect to plain form, not to ます (masu). 行きますと思う (ikimasu to omou) is wrong; 行くと思う (iku to omou, "I think I'll go") is right.

Picking a register: the practical rule

When in doubt, use です / ます (desu / masu) throughout. Being slightly too polite is a minor awkwardness; being too casual with a superior is a genuine social error. Japanese speakers will often soften their own speech down to match yours once the relationship is clear — nobody will read a polite foreign learner as stiff, but they will read a plain-form foreign learner as careless.

Note also that です / ます (desu / masu) is not keigo. Honorific and humble language — いらっしゃる (irassharu, "to go/come", honorific), いただく (itadaku, "to receive", humble) — is a separate system layered on top. Getting です / ます consistently right is already a solid level; see the keigo overview when you want the next layer.

Common mistakes for English speakers

1. Treating です (desu) as the verb "to be". English needs "is" in "the food is delicious", so learners insert です (desu) everywhere. But おいしいです (oishii desu) is not "delicious is" — です (desu) adds politeness to the sentence, it does not carry meaning. In plain form the same sentence is just おいしい (oishii, "delicious"), with no copula at all.

2. Pronouncing です (desu) as "deh-soo". In normal speech the vowel devoices: it sounds like "dess". Same for ます (masu), which sounds like "mass", and でした (deshita), which sounds like "deshta". This is not sloppiness — it is the standard pronunciation.

3. Making a question by word order. English inverts: "you are going" becomes "are you going?" Japanese keeps the word order and adds か (ka): 行きますか (ikimasu ka, "are you going?"). No inversion, no auxiliary.

4. Answering a negative question the English way. 行きませんか (ikimasen ka, "won't you go?") is answered はい、行きます (hai, ikimasu, "yes, I'll go") or いいえ、行きません (iie, ikimasen, "no, I won't go"). Japanese はい/いいえ answers the content of the sentence, not the polarity of the question the way English "yes/no" sometimes seems to.

5. Using ましょう (mashou) as a question. 行きましょう is "let's go", not "should we go?". If you want the other person's opinion, that is ませんか or ましょうか. English "shall we…?" blurs this, and learners carry the blur over — then sound like they are deciding for everyone.

6. Using ましょう (mashou) upward. It can read as herding your boss. Use ませんか (masen ka) or ましょうか (mashou ka) when the other person outranks you; see the politeness options under keigo.

7. Sticking to plain form with strangers because it feels "honest". In English, casual register just sounds relaxed. In Japanese, plain form toward someone you have not been invited to be close to reads as either childish or dismissive. Default to です / ます until the other person drops first.

8. Forgetting that い-adjectives already inflect. 高いでした (takai deshita) is wrong; the past of 高い (takai) is 高かった (takakatta), so the polite past is 高かったです (takakatta desu). です (desu) never does the tense work for an い-adjective.

Summary

Polite Japanese is one system with a small number of moving parts: です (desu) for nouns and adjectives, ます (masu) for verbs, ました / でした (mashita / deshita) for the past, ません / じゃないです (masen / ja nai desu) for the negative. On top of that, ましょう (mashou) proposes, ませんか (masen ka) invites, and ましょうか (mashou ka) offers while checking. Learn the register as a unit and switch it on for anyone you have not been given permission to be casual with.

Practice switching registers inside real sentences: on romaji.live the same scene appears with both polite and plain lines, so you type 行きます and 行く back to back and feel which one fits whom. Start from the kana table if you are still building speed, convert any word you meet with the romaji tool, then read keigo when you want the layer above this one.