Chapter 13 — い-Adjectives

Japanese has two types of adjectives. They look different, conjugate differently, and attach to nouns differently. This chapter covers the first type: い-adjectives. The next chapter covers the second type: な-adjectives.

い-adjectives are one of the four predicate types in Japanese, alongside verbs, な-adjectives, and noun-copula sentences. You have already seen their plain forms in Chapter 12's summary table. This chapter takes that preview and turns it into full working knowledge. By the end, you will be able to identify い-adjectives, conjugate them in all four forms (plain and polite), chain them together, and use them to modify nouns.

13.1 What Is an い-Adjective?

い-adjectives are words that describe qualities — size, temperature, cost, difficulty, taste — and end in い in their dictionary form. That final い is not just a coincidence of spelling. It is the conjugation ending. It changes when you negate, form the past, or connect to another clause. The い is what makes these adjectives alive.

Here are some い-adjectives you can recognize on sight:

たかい (expensive, tall) やすい (cheap) おおきい (big) ちいさい (small) あたらしい (new) ふるい (old)

Every one of these ends in い. Every one of them conjugates by changing that final い. This regularity is the core fact of this chapter.

Not everything ending in い is an い-adjective

This is the one trap. A small number of words end in い but are actually な-adjectives. The most common at this level are:

• きれい (clean, pretty) — な-adjective
• ゆうめい (famous) — な-adjective

These words do not conjugate like い-adjectives. きれい does not become きれくない. It becomes きれいじゃない, following the な-adjective pattern. The reason is etymological: きれい comes from the kanji 綺麗, where the final い is part of the word's root, not a conjugation ending. You will learn the な-adjective system in Chapter 14. For now, simply note that きれい and ゆうめい are exceptions. When you encounter a new adjective ending in い, a dictionary will tell you which type it is.

13.2 The Four Forms

い-adjectives conjugate across two dimensions: tense (non-past versus past) and polarity (affirmative versus negative). This gives four forms. Each form has a plain version and a polite version.

The adjective たかい serves as the model:

The plain forms are on the left of each slash. The polite forms are on the right. Notice that the polite forms simply add です to the plain forms. です here is not the copula — it is a politeness marker. The adjective does the real conjugation work on its own.

How the conjugation works

Every い-adjective has a stem: everything before the final い. For たかい, the stem is たか. For おおきい, the stem is おおき. For あたらしい, the stem is あたらし. You produce all four forms by attaching different endings to this stem.

Non-past affirmative: stem + い (the dictionary form itself)

たか + い → たかい

Non-past negative: stem + くない

たか + くない → たかくない

Past affirmative: stem + かった

たか + かった → たかかった

Past negative: stem + くなかった

たか + くなかった → たかくなかった

That is the entire system. Four endings: い, くない, かった, くなかった. Attach any of them to the stem of any い-adjective, and you have a correct form.

Why this pattern is familiar

You already know this system. In Chapter 12, you learned that the verbal negative suffix ない conjugates like an い-adjective: ない → なかった. That is the same rule at work here. The い-adjective negative ending くない itself contains ない — and when you want the past negative, you conjugate that ない into なかった, giving you くなかった. The logic is perfectly consistent.

Polite forms

To make any plain form polite, add です after it:

There is one alternative polite negative: たかくありません (non-past) and たかくありませんでした (past). These are slightly more formal. Both versions are correct. たかくないです is more common in everyday polite speech. たかくありません appears more often in writing and formal contexts. Use whichever feels natural; understand both.

More adjectives conjugated

To confirm the pattern is regular, here are three more adjectives in all four plain forms:

Every adjective follows the same pattern. No exceptions exist within the regular い-adjective class. There is exactly one irregular い-adjective, covered in Section 13.5.

Example sentences

Non-past affirmative:

この みせは たかいです。 "This store is expensive."

Non-past negative:

きょうは さむくないです。 "Today is not cold."

Past affirmative:

きのうの テストは むずかしかったです。 "Yesterday's test was difficult."

Past negative:

あの えいがは おもしろくなかったです。 "That movie was not interesting."

13.3 Prenominal Use: Adjective Before a Noun

い-adjectives can appear in two positions: as the predicate of a sentence (what you just learned) or directly before a noun to modify it. When an い-adjective modifies a noun, it goes immediately before the noun with nothing in between.

たかい やま "a tall mountain"

あたらしい ほん "a new book"

おおきい まち "a big city"

つめたい みず "cold water"

No particle, no copula, no connecting word is needed. The い-adjective simply sits before the noun. This is one of the things that makes い-adjectives different from な-adjectives, which require な between the adjective and the noun (covered in Chapter 14).

Prenominal い-adjectives can appear in full sentences:

たかい やまが みえます。 "A tall mountain is visible."

あたらしい ほんを かいました。 "I bought a new book."

ちいさい こうえんで あそびました。 "I played in a small park."

You can also use the negative or past forms before a noun, though this is less common:

たかくない レストランを さがしています。 "I am looking for a restaurant that is not expensive."

ふるかった くるまを うりました。 "I sold the car that was old."

The adjective retains its full conjugated form even when modifying a noun.

13.4 て-Form: Chaining Adjectives and Clauses

い-adjectives have a て-form, just as verbs do. It is used to chain multiple descriptions together or to connect an adjective clause to a following clause.

Formation

Replace the final い with くて.

たかい → たかくて やすい → やすくて おおきい → おおきくて おもしろい → おもしろくて

This is the same stem + く pattern you already know from the negative form, with て added instead of ない.

Chaining adjectives

When you want to describe something with two or more い-adjectives, use the て-form for all but the last:

この レストランは やすくて おいしいです。 "This restaurant is cheap and delicious."

あの へやは ひろくて あかるいです。 "That room is spacious and bright."

このまちは おおきくて にぎやかです。 "This city is big and lively."

Notice the last example: おおきくて (い-adjective て-form) connects to にぎやか (a な-adjective). The て-form can bridge between different predicate types.

Connecting to a following clause

The て-form can also link an adjective description to a consequence or related statement, similar to how verb て-forms chain clauses:

この ほんは やすくて よかったです。 "This book was cheap, and that was good."

しけんが むずかしくて こまりました。 "The exam was difficult, and I was troubled."

へやが せまくて つくえを おけません。 "The room is small (narrow), so I cannot put in a desk."

In these sentences, the て-form creates a loose "and" or "so" connection. It implies that the first description is related to or leads to the second statement. It does not specify the exact logical relationship — context does that.

13.5 The Irregular いい / よい

The adjective meaning "good" is いい. It is the only irregular い-adjective in the language. The irregularity is simple: いい is used only in the non-past affirmative (dictionary) form. Every other form uses the stem よ-, from the older form よい.

The て-form is also from the よ- stem:

よくて

Here is the critical point: いい is the only form that uses いい. The moment you conjugate — negate, make past, chain with て — you switch to よ-. いくない, いかった, and いくて do not exist.

Sentences:

このみせは いいです。 "This store is good."

きのうの てんきは よかったです。 "Yesterday's weather was good."

あの レストランは よくないです。 "That restaurant is not good."

やすくて よかったです。 "It was cheap and that was good."

Compound adjectives built on いい follow the same pattern. かっこいい ("cool-looking") becomes かっこよかった in the past and かっこよくない in the negative. The いい portion always shifts to よ- when conjugated.

Memorize this irregularity. It is the only one. Every other い-adjective in the language is perfectly regular.

13.6 Common い-Adjectives

Below are 25 い-adjectives you should learn at this level. They are organized in semantic pairs where natural opposites exist. The pitch accent pattern is marked with the standard notation: ꜜ indicates where the pitch drops.

Cost and size

Length and age

Temperature

Note: あつい appears twice. The two words are written with different kanji (暑い for weather, 熱い for touch) but are pronounced identically. Context makes the meaning clear: さむい pairs with weather-あつい, while つめたい pairs with touch-あつい.

Taste

Speed and time

Quality and character

Difficulty and distance

One more

Learn these as pairs wherever possible. When you know たかい, learn やすい at the same time. When you know あたらしい, learn ふるい. Opposites reinforce each other.

13.7 Putting It All Together

You now have the full い-adjective system. Here is a summary of everything you can do with any regular い-adjective:

Predicate use — the adjective is the main description in the sentence:

この やまは たかいです。 "This mountain is tall."

きのうは さむかったです。 "Yesterday was cold."

Prenominal use — the adjective modifies a noun:

たかい やまに のぼりました。 "I climbed a tall mountain."

て-form chaining — connecting descriptions:

このまちは おおきくて にぎやかです。 "This city is big and lively."

Inside embedded clauses — using the plain form before grammar patterns (as previewed in Chapter 12):

この ほんは むずかしいと 思います。 "I think this book is difficult."

やすかったから かいました。 "I bought it because it was cheap."

These four uses cover the vast majority of い-adjective appearances in Japanese. The forms are regular. The only irregularity is いい/よい. Everything else follows from stem + ending.

13.8 Chapter Summary

い-adjectives end in い and conjugate by replacing that い with a different ending:

• Negative: くない
• Past: かった
• Past negative: くなかった
• て-form: くて

Adding です after any plain form produces the polite version.

い-adjectives modify nouns directly with no particle between them: たかい やま. They chain with other descriptions using the て-form: やすくて おいしい.

The adjective いい (good) is the only irregular member of this class. It uses the よ- stem for all conjugated forms: よくない, よかった, よくなかった, よくて.

な-adjectives — the other adjective type — behave differently in every respect. That is the subject of Chapter 14.

13.9 Reading Passage — にほんの しき

にほんには しきが あります。はる、なつ、あき、ふゆです。

はるは あたたかいです。さくらが きれいで、こうえんに ひとが おおいです。てんきが よくて、そとを あるくのが たのしいです。

なつは とても あついです。うみが きれいで、たくさんの ひとが およぎに いきます。でも、むしあついです。あつすぎて、そとに あまり でたくないです。つめたい のみものが おいしいです。

あきは すずしくて きもちがいいです。やまの きが あかくて きいろくて、とても きれいです。たべものも おいしいです。あきは くだものが あまくて、とても いいです。

ふゆは さむいです。ゆきが ふる ところも おおいです。さむくて そとに でたくないですが、おんせんの おゆが あたたかくて きもちがいいです。

わたしは あきが いちばん すきです。あつくなくて、さむくなくて、たべものが おいしくて、けしきが きれいです。にほんの しきは とても うつくしいです。

Translation

Japan has four seasons: spring, summer, autumn, and winter.

Spring is warm. The cherry blossoms are beautiful, and parks are full of people. The weather is good, and it is enjoyable to walk outside.

Summer is very hot. The ocean is beautiful, and many people go swimming. But it is humid. It is too hot, and you don't really want to go outside. Cold drinks are delicious.

Autumn is cool and pleasant. The mountain trees turn red and yellow, and it is very beautiful. The food is also delicious. In autumn, fruits are sweet, and that is very nice.

Winter is cold. There are also many places where snow falls. It is cold and you don't want to go outside, but the hot spring water is warm and pleasant.

I like autumn the best. It is not hot, it is not cold, the food is delicious, and the scenery is beautiful. Japan's four seasons are very beautiful.

Notes on the Passage

しき — "four seasons." し (four) + き (season).

あるくのが たのしいです — "walking is fun." The の turns the verb あるく into a noun phrase. This nominalization is formally introduced later.

むしあつい — "humid and hot." A compound い-adjective.

あつすぎて — "too hot, and..." すぎる (too much) attached to the adjective stem あつ-, then in て-form for chaining.

あかくて きいろくて — "red and yellow and..." Two い-adjectives chained using the くて form.

あまくて — "sweet and..." The て-form of あまい (sweet).

あつくなくて、さむくなくて — "not hot and not cold." The negative て-form: くない → くなくて.

Vocabulary

New words introduced in this chapter: