In Japanese
い-Adjectives are known as ‘form containing words’, and are used to describe nouns. All
い-Adjectives end in い in their base form.
-
温（ぬる）い水（みず）。
Lukewarm water.
-
狭（せま）い道（みち）。
Narrow road.
As mentioned, all
い-Adjectives end in い in their base form. However, not all words ending in い are
い-Adjectives. Let’s take a look at some of the words that are commonly mistaken for
い-Adjectives.
In きれい’s case, it actually comes from the kanji structure 綺麗（きれい）, with い being part of the kanji itself. This is never the case with
い-Adjectives, where the い will always be outside of the kanji. Due to the kanji for 綺麗（きれい） being somewhat difficult, this word is often written in hiragana or katakana, which leads to confusion for learners. Unfortunately there is no rule for distinguishing which words ending in い are not
い-Adjectives, but thankfully, there are not very many of them, so it won’t be long before you become familiar with them.
Unlike
な-Adjectives,
い-Adjectives must never be followed by
だ. This is due to
だ only being able to conjugate with nouns (which
な-Adjectives originally are). Instead,
です is used with
い-Adjectives to make them sound more polite.
-
日本の道（みち）は、狭（せま）いです。
Japan’s roads are narrow.
-
温泉（おんせん）の風呂（ふろ）は熱（あつ）いです。
The onsen’s baths are hot.
Although using です with い-Adjectives is very common, it is actually incorrect Japanese. As です is simply a polite variation of だ, it follows all of the same conjugation rules as だ. This means that it should only be attached to nouns and な-Adjectives. However, as most Japanese natives do not know this rule, it is widely considered natural to use.