tanoshikatta desu ...vs... tanoshii deshita

[Kurious]

Hello!

I've heard "tanoshikatta desu" a few times. I've never heard "tanoshii deshita" but I'm wondering if something like that can be considered acceptable Japanese.

Thanks!

[LordOfTheFlies]

Tanoshii deshita isn't used at all. You always say tanoshikatta desu when using the long forms.

I-adjectives are conjugated as following for their long forms:
Present, just add です

Remove the い and add the following
Past ～かったです
Negative present ～くありません or ～くないです
Negative past ～くありませんでした or ～くなかったです

There's just one exception you have to remember. The i-adjective いい is an alternate spelling/pronounciation derived from the original adjective よい with the same meaning. The tricky part is that even though using いい is fine, you have to conjugate the other forms using よい、 eg よくない　よくなかった　よかった

[Kurious]

Thanks! I did know about some of these forms, but I didn't know about 「～くありません」 nor 「～くありませんでした」。 I mean, I understand them as I read them, but I wasn't aware that they're the same as the forms ending in 「～です。」... or is there any difference? Since statements ending in 「～です。」 are already polite, then... is there a significant difference between the two?

(I want to mention that I have been studying intermediate books for a while now (much more in the area of vocabulary than in the area of grammar) but, of course, there is so much to learn. My understanding of polite forms is limited to the 「～ます。」 conjugations, my noticing of the 「お-」 and 「ご-」 prefixes, and a few words like 「召し上がる」 and 「参る」. But I haven't studied polite forms in detail.)

Thanks in advance.

[furrykef]

Thanks! I did know about some of these forms, but I didn't know about 「～くありません」 nor 「～くありませんでした」。 I mean, I understand them as I read them, but I wasn't aware that they're the same as the forms ending in 「～です。」... or is there any difference? Since statements ending in 「～です。」 are already polite, then... is there a significant difference between the two?

The ～くありません forms are more formal than the ～くないです forms. Note that "formality" and "politeness" are different things... formal language is usually polite by nature, but polite language isn't necessarily formal. (For example, you'd still use contractions in everyday polite speech, but contractions are informal and so won't appear in academic writing, speeches, etc.) So if you're talking to somebody on the street, you're more likely to hear the ～くないです forms.

[Kurious]

I see! Thanks for explaining that, it really helps!