[Genki I Notes #1] な and い adjectives

The Japanese language has two forms of adjectives: な and い.

The な and い denote the last syllables when the adjectives modify nouns.
ex.
あも白い映画 (interesting movie)
綺麗な写真 (beautiful picture)

when they are used in a phrase to describe something (as in a “be” phrase), the two forms are conjugated differently according to tense (present vs past) and polarity (affirmative vs negative).

な adjectives — replace the final な:

	Affirmative	Negative
Present	です	じゃないです
Past	でした	じゃなかったです

い adjectives — replace the final い:

	Affirmative	Negative
Present	いです	くないです
Past	かったです	くなかったです

all forms end with です with the exception of the past affirmative form of な adjectives, which ends with でした. The past affirmative form of い takes the かった before ending as usual with です

The negative form of な starts with じゃな and い with くな. For present form, it follows with い. For past form, it follows with かった. They all end normally with です.

The only exception to this conjugation is the adjective いい (good). It is conjugated like い adjective but the word itself changes to よ in all forms except for present affirmative.
ex.
いいです
よくないです
よかったです
よくなかったです

い adjective always end in い. な adjective typically do not end in い, but there are exceptions such as きれい and 嫌い.

Very interesting — this is a unique linguistic feature not seen in Korean, English, or Spanish.