です is a copula, or a word (verb) that connects two words. The best equivalent in English would be the verb "to be". However, です can often be used as merely a politeness marker which has no English equivalent. It is not conjugated like the other verbs.
- Kanatenshi asked if "desu" can be used in place of "imasu" as in: gakko ni imasu =/= gakko ni desu?
- Keatonatron chimed in suggesting to think of "desu" as an equal sign instead of as "to be."
- Yudan Taiteki mentioned "desu" can also act as a politeness marker after -i adjectives and suggests this test:
"akai" means "is red" (not just "red"), so the "desu" doesn't supply any additional meaning other than politeness. I think the clearest way to see that is with から. 先生から means "from the teacher" (e.g. 先生からの手紙) whereas 先生ですから means "because [he?] is a teacher", so it's clear there that です is adding the meaning of "to be", and that there is a difference between 先生 and 先生です. But with 赤い, both 赤いから and 赤いですから means "because it is red", so the です is just adding politeness and nothing else. It's why you can't put だ after 赤い, but you can put it after 先生.
です goes at the end of a sentence to mean "to be (is, are, etc.)". It is conjugated in the present and past as so:
Present Affirmative: です Present Negative: ではありません Past Affirmative: でした Past Negative: ではありませんでした
The plain form of です, だ, also has somewhat irregular conjugations:
Present Affirmative: だ Present Negative: ではない (じゃない in spoken language) Past Affirmative: だった Past Negative: ではなかった (じゃなかった in spoken language)
- プードルは、ヒツジではありません。(See this thread.;)