I-Adjectives & Na-Adjectives

There are two types of adjectives in Japanese: i-adjectives and na-adjectives. The type of adjective is determined by its ending or—more precisely—the grammar that is required to join the adjective to nouns or transform the adjective into an adverb. Fortunately, it is obvious in almost all cases when looking at a new adjective whether it is an i-adjective or a na-adjective so you aren’t faced with the challenge of rote learning groups.

Here I’ll introduce i-adjectives and na-adjectives and their respective conjugations—yes, adjectives conjugate in Japanese! In English, adjectives themselves don’t transform when we talk in the negative, past, or past negative tense. In other words, in the following sentences the word “expensive” does not change.

The shoes are expensive.

The shoes are not expensive.

The shoes were expensive.

The shoes were not expensive.

The other thing you might notice is that some adjectives in Japanese are not adjectives in English. For instance, the most common way of saying “to like” uses “like” as an adjective.

I-Adjectives

All i-adjectives end in い which is written in hiragana. Below is a selection of JLPT N5 i-adjectives.

English	Japanese
Good	いい
Cheap	安やすい
Kind	優やさしい
Light	明あかるい
New	新あたらしい
Busy	忙いそがしい
Big	大おおきい
Interesting	面白おもしろい
Fun, enjoyable	楽たのしい
Old	古ふるい

The conjugation for i-adjectives always follows the same rules with just one exception: the adjective “good” (いい). Here you only have to remember that when the adjective conjugates into the past, negative, or past negative the first syllable becomes よ.

In fact, よい is the archaic word for good. It is still used today in formal writing but rarely in conversation in this standard form.

The other critical grammatical point to note is that we cannot add the standard form of the auxiliary verb to i-adjectives (this is the one exception to rule that all sentences must end with a verb in Japanese). For example, “this is cheap”:

これは　安やすいだ。(✘)

これは　安やすい。(✔)

Negative & Past Negative

For the negative and past negative we change the い to a く and then add the standard conjugation of the verb ある (the verb “to exist” for inanimate objects) which we met earlier.

English	Dictionary	Negative	Past Negative
to exist	ある	ない	なかった

For example, to say “not expensive”:

高たかい　→　高たかく　→　高たかくない

English	Dictionary	Negative	Past Negative
Cheap	安やすい	安やすくない	安やすくなかった
Big	大おおきい	大おおきくない	大おおきくなかった

Past Tense

For all other i-adjectives you simply change the final い to かった. Take the adjective for “tall” or “expensive” (たかい), for example:

高たかい　→　高たかかった

For the adjective “good” the past conjugation becomes:

いい　→　よかった

Polite Conjugations

For the polite conjugation we follow exactly the same rules as above, but add the polite form of the auxiliary verb: です.

Standard	Polite
いい	いいです
Good	Good

Standard	Polite
よかった	よかったです
Was good	Was good

Standard	Polite
よくない	よくないです
Is not good	Is not good

Standard	Polite
よくなかった	よくなかったです
Was not good	Was not good

For the negative and past negative we can also use the polite conjugation for ある instead.

English	Polite Present	Polite Negative	Polite Past Negative
to exist	あります	ありません	ありませんでした

Polite I	Polite II
よくないです	よくありません
Is not good	Is not good

Polite I	Polite II
よくなかったです	よくありませんでした
Was not good	Was not good

Both ways of conjugating to the negative and past negative are used in Japanese; however, the latter is arguably more polite.

Na-Adjectives

Na-adjectives can be conveniently defined as all those that don’t end with い with just a few exceptions.  The exceptions are “beautiful” (きれい), “hate” (きらい), and “grateful/happy” (さいわい) which look like い adjectives, but in fact conjugate as na-adjectives. Below is a selection of JLPT N5 na-adjectives.

English	Japanese
Like	好すき
Famous	有名ゆうめい
Quiet	静しずか
Convenient	便利べんり
Important, precious	大切たいせつ
Skilful, good at	上手じょうず
Unskilful, not good at	下手へた
Necessary	必要ひつよう
Splendid	立派りっぱ
Serious	まじめ

Grammatically speaking, we must append the auxiliary verb to na-adjectives; however, in casual conversation this will very often be omitted.

私わたしは　好すきだ。

I like (it).

私わたしは　きらいだ。

I hate (it).

Because na-adjectives take the auxiliary verb we already know their conjugation. We just need to conjugate the auxiliary verb to get the negative, past, or past negative for both the standard and polite forms.

Tense	Standard	Polite
Present	好すきだ	好すきです
Past	好すきだった	好すきでした
Negative	好すきではない	好すきではありません
Past Negative	好すきではなかった	好すきではありませんでした

私わたしは　好すきではありませんでした。

I didn’t like (it).

And, as we’ve seen before, in both cases we can replace では with the more colloquial じゃ.

私わたしは　好すきじゃありませんでした。

I didn’t like (it).