Summary: い-adjectives are a type of adjective in the Japanese language that are used to describe nouns. They can take different endings to change their meaning, such as expressing tense and truth value. The stem form of an い-adjective is the part of the word that remains the same regardless of the ending. い-adjectives can be used either at the end of a sentence to describe the subject or directly before a noun without a particle. New い-adjectives are rare, but they can be formed by abbreviating existing ones or derived from loan words. There are two types of い-adjectives: those ending in 〜い, which describe physical characteristics, and those ending in 〜しい, which describe personal or emotive characteristics.
This is the major way in which they differ from な-adjectives, which rely on an additional word (だ or です) to show tense and truth information. (View Highlight)
Its kanji form 良い can be read as either いい or よい without any difference in meaning (though よい sounds more formal). (View Highlight)
良い ＝ いい or よい
良かった ＝ only よかった
良くない ＝ only よくない (View Highlight)
This applies to い-adjectives that include いい, such as かっこいい (cool), which comprises 格好 (appearance) and いい (good). (View Highlight)
Unlike かっこいい, かわいい does not include いい, despite having two い characters on the end. The kanji form of this word is 可愛い, with only one い on the end. The first い is part of the reading of the kanji 愛 (わい). So it conjugates like any other い-adjective. (View Highlight)
To show that something is negative, the ending 〜くない replaces 〜い. For example, 面白い (funny) becomes 面白くない (not-funny): (View Highlight)
To show the past tense, い-adjectives end in 〜かった. For example, 寒い (cold) becomes 寒かった (was cold): (View Highlight)
い-adjectives can be used in two different positions to describe a noun. You’ll find it either at the very end of a sentence, or directly before a noun. (View Highlight)
When used at the end of a sentence, い-adjectives describe the subject of the sentence. (View Highlight)
Unlike な-adjectives, which require a particle to attach to a noun, い-adjectives can appear directly before a noun without a particle between them. (View Highlight)
い-adjectives tend to cover the most fundamental, “primal” concepts, such as basic colors and emotions, temperature, flavor, size, and so on. (View Highlight)
As with most native Japanese words, い-adjectives are a closed class, which means that it’s very rare for new ones to appear. (View Highlight)
い-adjectives with 〜い endingsーlike 暑い (hot), 高い (high/expensive), and 青い (blue)ーgenerally describe physical characteristics like temperature, size, and color. (View Highlight)
い-adjectives with 〜しい endings, on the other hand, tend to be used for more personal, emotive or “internal” characteristics, such as 楽しい (fun), 苦しい (painful) and 悲しい (sad). (View Highlight)
Because 〜しい adjectives are personal and subjective, they are generally only appropriate for describing our own feelings. So we can say 楽しい when we’re having fun, but not when we think someone else is having fun. (View Highlight)
Many 〜しい adjectives have corresponding verbs, to allow us to talk about how other people appear to be feeling. Some examples of these verbs include 楽しむ (to have fun), 苦しむ (to suffer) and 悲しむ (to be sad) (View Highlight)