7.5.1. Nonpast forms
English adjectives are more similar to nouns than to verbs, and they require the copula be to become predicators. On the other hand, Japanese adjectives are more similar to verbs, and they don't need a copula. They have inflexion like verbs.
All Japanese adjectives end with the hiragana い "i" if they are in the non-past form. An adjective consists of a stem and a suffix as verbs do, and the stem never changes while suffixes can change. The final /i/ in the non-past form of an adjective is the suffix, and the rest is the stem. Please note that the suffix for the non-past form of verbs is /u/, and that of adjectives is /i/.
Here are some adjectives:
Since adjectives always end with the hiragana い, the stem of an adjective always ends with a vowel. Japanese adjectives are similar to verbs, so you can consider them to be a combination of the copula be and an adjective in English.
Adjective Stem Suffix Meaning よい
yo -i is good あつい
a tu i
atu -i is hot うれしい
u re si i
uresi -i is glad おいしい
o i si i
oisi -i is tasty
These are examples of adjectives:
Kana: すしはおいしい。 Romanization: Su si wa o i si i . Structure: (noun, sushi) (topic marker) (adjective, is tasty) Meaning: Sushi is tasty.
7.5.2. Past forms
Kana: きものはうつくしい。 Romanization: Ki mo no wa u tu ku si i . Structure: (noun, kimono) (topic marker) (adjective, is beautiful) Meaning: Kimonos are beautiful.
Add the suffix かっ "-katta" to the stem of an adjective to create its past form.
This is an example of the past form of adjectives:
Nonpast form Meaning Past form Meaning よい
is good よかった
yo ka t ta
was good あつい
a tu i
is hot あつかった
a tu ka t ta
was hot うれしい
u re si i
is glad うれしかった
u re si ka t ta
was glad おいしい
o i si i
is tasty おいしかった
o i si ka t ta
7.5.3. Polite forms
Kana: すしはおいしかった。 Romanization: Su si wa o i si ka t ta . Structure: (noun, sushi) (topic marker) (adjective, was tasty) Meaning: The sushi was tasty.
Adjectives don't have a politeness suffix like verbs' politeness suffix ます "masu", so you have to add the polite copula です "desu" to the end of an adjective to make it polite. Make the past form of an adjective first, then add です "desu" to it to make its polite past form.
Kana: すしはおいしいです。 Romanization: Su si wa o i si i de su . Structure: (noun, sushi) (topic marker) (adjective, is tasty) (suffix, polite mode)
The polite past-form adjectives don't end with た "ta" because of the politeness suffix. Making the polite form before making the past form is not allowed for adjectives, which would produce おいしいでした "oisiidesita" in the case of the second example shown above.
Kana: すしはおいしかったです。 Romanization: Su si wa o i si ka t ta de su. Structure: (noun, sushi) (topic marker) (adjective, was tasty) (suffix, polite mode)