Grammatical question
 

I am studying Japanese and I have met a certain point where a certain grammar rule is not clear. I asked already to 4 Japanese people, 2 said it is correct and 2 said it is incorrect. At this point I think I will never use this form, but I am just curious to see if I get some better explaination. It is about I Adjectives.
I know the true adjective past tense is obtained by changing the い with かった to which I can add です to make it polite. For example:
この映画は面白い==>この映画は面白かった==>この映画は 面白かったです。
Now so far is all ok, it is reported in every grammar book and internet. But I have found a new form of the past for the true adjectives that I see used in internet, I can't find on grammar books and as I said 2 Japanese people said it is correct and 2 said it is incorrect. This is the form I am talking about...
この映画は面白いでした。

Hopefully I will receive answers that will clear this puzzle I have in my mind :)
Thanx in advance.

I'm just a student as well and can't tell you with any certainty that it's wrong. But whenever I've accidentally used でした　with an i-adjective, I was told it was wrong and had to change it to かったです.

Of course there are adjectives that end in "i" that are actually na-adjectives which you would use でした with.
Ex:
町がきれいでした。
両親が元気でした

If I remember to do so, I'll ask my teacher tomorrow to see if I can get you a more definite answer.

この映画は面白いでした。

面白い is an い-adjective, therefore it is incorrect to put it in the past tense like a noun.

This is never a grammatically correct sentence.

Yea that is most of the people I asked told me. But if you go on yahoo Japan there is well almost 三万人 that use this expression. If I typed on a search engine a grammatical error in my language (Italian) I might get few tens or maybe a hundred result, probably all typos or a few not speaking well Italian.
But I can't believe 30,000 Japanese speak bad Japanese.
Last time I encountered it if I well remember it was on the NTV's forum (Japanese channel) one of the messages had in it a phrase ending よいでした。
As I said I will never use it, but for someone who doesn't speak any Japanese, hearing so many Japanese people using it and (one of them comes to my dojo so he told me in my face it is correct) gives me doubts.

Might be some dialect or old expression?

It sounds like a very childish or maybe slangy or lazy way of speaking.

If there are only 30,000 hits, then that hardly makes a phenomenon. At the same time, Japanese people aren't robots. They use slang and poor grammar, too.

I searched "I ain't" in Google, a phrase which is never correct grammatically and got over 13 million hits.

K thank you very much.



BTW on a side note...ain't is on dictionaries and some schools even started accepting it.

It's still never correct grammar.

Tell me who those two people were who said that sentence was correct. I'll sue them.

Hello. I'm Hirashin from Kyoto, Japan.

Yup. Some Japanese people write funny sentences either intentionally or unintentionally.

As you may already know, most people avoid using the structure as in 面白いでした. But some people might say that for fun though that would not sound right.

Also, I know some young people who say すきくない or きれいくない, which should be すきじゃない/すきではない or　きれいじゃない/きれいではない.

If you are not a skilled speaker/writer of Japanese yet, it would be better to follow what your grammar book says.

Later,

ひらしん:)

Thanx everyone for your explainations.