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I said to a Japanese person last night, meaning to say "I'm tired":


She corrected me to:


I'm curious as to why this is. I thought つかれたです was grammatically correct. Does it sound strange or unusual? And why would using the past tense "I felt tired" be preferable to the present tense "I feel tired"?

Please reply in kana or kanji with furigana only.

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up vote 7 down vote accepted

Usually, です is a polite copula, similar to だ but more polite:

それはリンゴだ  That is an apple
それはリンゴです That is an apple (polite)

But です can also be a politeness marker added to adjectives:

あかい    is red
あかいです  is red (polite)

When it's a politeness marker, です doesn't inflect for tense:

あかいです    is red (polite)
あかかったです  was red (polite)

The adjective before it already inflects for tense.

This is a relatively recent innovation in the Japanese language and not too long ago was considered unacceptable. Some people still try to reword things to avoid it, but it's probably caught on because it filled a useful gap in the language: making adjectives polite, like です with nouns or 〜ます with verbs, but without going as far as 〜うございます.

However, verbs already have a way to make them polite:

つかれた    (past)
つかれました  (past, polite)

So there's no motivation to start saying *つかれたです, and there's no reason for people to start treating it as an acceptable part of the Japanese language. As a result, it's ungrammatical.

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I see, so つかれた is a plain past tense verb, not an adjective? – Leo King Apr 8 '14 at 11:09
Yes, it's the past tense of the verb つかれる "be / become tired". – snailplane Apr 8 '14 at 11:11
Ah, わかります。 So つかれたです was grammatical, but now the grammatical method is to inflect the verb and leave out the sentence ending. – Leo King Apr 8 '14 at 11:15
It was never grammatical to add です to verbs. There was a motivation to add です to adjectives, so over time it became acceptable. But there was no such motivation for verbs, because verbs already had the 〜ます ending to make them polite. That is what I tried to explain. – snailplane Apr 8 '14 at 11:20
Okay, I understand. Thank you! +1 and accepted. – Leo King Apr 8 '14 at 11:25

To form the polite past tense, you can't just add です to the non-polite past tense つかれた.

You need to make the polite present tense つかれます into the past tense (i.e. ます -> ました) つかれました.

That the ending ます inflects like any other verb, e.g. (present) はなす -> (past) はなした, is no accident. ます can be thought of as an auxiliary verb.

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I know that つかれまひた is polite past tense. I'm not asking what it is, I'm asking why I need to use it. Why can't I simply use the adjective つかれた with present tense sentence ending です? – Leo King Apr 8 '14 at 9:52
Because it's ungrammatical. (BTW, つかれた is not an adjective.) – Earthliŋ Apr 8 '14 at 9:53

Japanese grammar works in a different way when it comes to forming polite forms of verbs and i-adjectives.

For verbs, you add ~ます to the verb and then you form all other verbs forms from combined polite verb:

つかれる -> つかれます plain -> polite

つかれます -> つかれました polite -> polite past

つかれます -> つかれません polite -> polite negative

It is different for i-adjectives though. In that case, you use the plain form of adjectives and just add です.

おいしい -> おいしいです plain -> polite

おいしかった -> おいしかったです plain past -> polite past

おいしくない -> おいしくないです plain negative -> polite negative

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