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

> つかれたです。

She corrected me to:

> つかれました。

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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2014-04-08T09:41:21.057
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grammar usage verbs
Why should I use つかれました and not つかれたです
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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2014-04-08T09:47:42.230
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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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2014-04-08T10:04:30.943
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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](https://japanese.stackexchange.com/q/765/1478).

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 think you have the grammar right, what might have escaped you is that つかれた
is not an adjective like "tired" is in English (ex: He is tired.) . When you
realize that it's a past tense of a verb and you have to treat it like
食べる・食べた, everything will make sense to you. You'd say, 食べました but not 食べたです。

To repeat everyone here, 「です」applies only to adjectives. That's why

つかれたです

....is actually gramatically incorrect. And if I may, it's the kind of wrong
that really, really sounds wrong so you want to get this right.
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