～ます／です

～ます (on verbs) and です (on nouns and adjectives) mark the polite style which is the standard way to speak to strangers, teachers, coworkers, and customers. They appear in all their forms: ます, ました, ません, ませんでした, です, でした.

Politeness is its own layer. Past and negative are separate ideas that stack on top of it: 食べませんでした = polite + negative + past = “did not eat”.

1. Polite non-past with ～ます

Attach ます to the verb's masu-stem for a polite present or future statement.

2. Polite statements with です

です follows nouns, na-adjectives, and i-adjectives (高いです) to make the sentence polite.

3. Stacking with past and negative

The other endings ride on top of ます／です: past ました／でした, negative ません, and both together in ませんでした.

How to form it

Verb masu-stem (連用形) + ます: godan (u-verbs) shift the final syllable to the i-row (書く → 書き), ichidan (ru-verbs) drop る, and the irregulars are する → し and 来る → 来. Nouns and na-adjectives simply take です, and i-adjectives keep their own form and add です after it.

• 書く（かく）= to write → 書きます（かきます）= write (polite)
• 飲む（のむ）= to drink → 飲みます（のみます）= drink (polite)
• 食べる（たべる）= to eat → 食べます（たべます）= eat (polite)
• する = to do → します = do (polite)
• 来る（くる）= to come → 来ます（きます）= come (polite, special irregular case)
• 学生だ（がくせいだ）= is a student → 学生です（がくせいです）= is a student (polite)
• 高い（たかい）= expensive → 高いです（たかいです）= is expensive (polite)

Key idea

ます／です change nothing about the facts only about the relationship with the listener. 食べる and 食べます describe the same eating. The polite form simply shows respect to the person you are talking to.