Plain and polite forms

Every Japanese verb, adjective and です (desu) has two styles. The polite style ends in です (desu) or ます (masu). The plain style is the form you find in a dictionary: 食べる (taberu) instead of 食べます (tabemasu). Both mean exactly the same; only the tone changes.

To make the plain negative, u-verbs change their last sound to the a row and add ～ない (-nai): 飲む (nomu) → 飲まない (nomanai). A final う becomes わ: 買う (kau) → 買わない (kawanai). Ru-verbs drop る and add ～ない: 食べない (tabenai). The plain past is the te-form with て changed to た (and で to だ): 飲んで (nonde) → 飲んだ (nonda).

For い-adjectives the plain form is simply the polite form without です (desu): 高いです (takai desu) → 高い (takai). The negative and past endings are the same ones you already know.

For な-adjectives and nouns, です (desu) becomes だ (da). In writing and careful speech the negative is ではない (de wa nai); in conversation it is じゃない (ja nai).

Use the polite style with people you don't know well, with colleagues (especially older or senior ones), customers, shop and station staff, and anyone older than you whom you aren't close to. It is always safe.

Use the plain style with friends, family, children and close colleagues of your own age. Switching from polite to plain is a sign of growing closeness; it's usually the older or more senior person who starts.

Plain forms also appear inside polite sentences, whatever the situation: before と思います (to omoimasu), つもりです (tsumori desu), から (kara) and in front of a noun. Only the end of the sentence shows the politeness: 明日行くと思います (ashita iku to omoimasu), I think I'll go tomorrow.

Casual conversation is more than plain forms. Questions usually drop か (ka) and rise at the end instead: 行く？ (iku?), are you going? With nouns and な-adjectives, だ (da) is dropped in questions: 暇？ (hima?), are you free?

Particles like は (wa) and を (o) are often left out: これ、おいしいね (kore, oishii ne), this is tasty. At the end of a statement, a bare だ (da) can sound blunt, so it is often softened with よ (yo) or ね (ne), or dropped. はい (hai) becomes うん (un), and いいえ (iie) becomes ううん (uun).

Articles, reports, textbooks and information panels use a third style. It is plain, but nouns and な-adjectives take である (de aru) instead of だ (da): negative ではない (de wa nai), past であった (de atta). Verbs and い-adjectives are simply plain.

This style sounds neutral and objective. Don't mix it with です／ます in one text, and don't use it in conversation, where it sounds like reading aloud.

In relaxed speech, some common endings are shortened. You will hear them constantly between friends and in families, in films and on television. Use them only in casual speech, never in writing or with people you speak politely to.