What is an i adjective?

I adjectives are a form of adjective like atsui (熱い), "hot", or akai (赤い), "red" which end in an "i" syllable (い), and can change to negative forms by adding kunai. For example atsukunai, "it's not hot", or akakunai "it's not red". They also have past tenses, like atsukatta, "it was hot", or akakatta, "it was red". They can also become adverbs, atsuku moeru "burn hotly". Like Japanese verbs, the i adjectives can go at the end of sentences: Kyō wa atsui "It's hot today."

Here are some example i adjectives in negative and positive sentences:

Meaning Example Negative example
akai 赤い red Akai kuruma "A red car" Akakunai neko "A cat which is not red"
kowai 怖い scary Kowai eiga "A scary movie" Kowakunai inu "A dog which is not scary"
muzukashii 難しい difficult Muzukashii mondai "A difficult problem" Muzukashikunai shigoto "Work which is not difficult"
atarashii 新しい new Atarashii zubon "New trousers" Atarashikunai pasokon "A computer which is not new"
furui 古い old Furui tatemono "An old building" Furukunai tokei "A clock which is not old"
kawaii 可愛い cute Kawaii akachan "A cute baby" Kawaikunai neko "A cat which is not cute"

All i adjectives end in ai, ii, ui or oi. There are none ending in ei.

Not every word ending in i is an i adjective. For example, the word kirai "disliked" is an adjective, but the final "i" does not conjugate. Instead it takes na. For example, "food (I) dislike", is kirai na tabemono and "food I do not dislike" is kirai ja nai tabemono, with the final "i" not changing.

The other main kind of adjective is the "na" adjective such as kirai above. A few words come in both i adjective and na adjective forms, such as ōkii ("big") and ōki na ("big"). See What is the difference between and ?

Many adjectives related to human emotions are i adjectives which end in shii, for example tanoshii (楽しい), "enjoyable", kanashii (悲しい), "sad", or muzukashii (難しい), "difficult".

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