Why should I use つかれました and not つかれたです


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.




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.




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.

