Say something is becoming a certain way (〜くなる)
Drop the final い from an い-adjective and attach くなる to express a gradual or natural change of quality (“getting warmer”, “becoming expensive”).
Expressing Adjective Change of State (くなる)
saikin yoru wa samuku narimashita
Recently, nights have become cold.
い-adjective (くなる) vs Noun (になる)
Micro-Shift秋になって、だんだん 寒く なります。
寒い → 寒くなる (drop い, attach くなる)Autumn arrived, and it is gradually becoming cold.
Transforming an い-adjective into an adverbial state requires dropping い and adding くなる.
Example Sentences
It gradually becomes cold.
Spring came and it became warm.
The Phonological Shift: From Static Quality to Dynamic Transformation
Japanese い-adjectives describe static states or qualities: 寒い (it is cold), 高い (it is expensive). But what happens when the temperature drops or prices climb?
To describe change, Japanese converts the adjective into an adverbial form by replacing the final い with く. Appending the verb なる (to become) produces a fluid description of transformation:
- Static state: 寒い: “cold”
- Dynamic change: 寒くなる: “to get cold / become cold”
Everyday Transitions: Weather, Senses & Life
This pattern is fundamental for describing nature and everyday shifts:
- Weather & Environment:
- 暖かくなる: “get warm / warm up”
- 涼しくなる: “get cool / cool down”
- 暗くなる: “get dark (as evening falls)”
- Life & Growth:
- 忙しくなる: “get busy”
- 背が高くなる: “grow taller”
- 美味しくなる: “become delicious / improve in flavor”
The Irregular Classic: いい (Good) Becomes よくなる
Pay special attention to the word for “good”: いい. Just like in English where “good” shifts to “well” rather than “good-ly”, いい derives historically from よい. When changing its form, it always reverts to its classical stem よ:
- Incorrect:
*いくなる(never exists!) - Correct: よくなる: “to get better / improve / recover”
- 天気がよくなりました: “The weather got better.”
Natural Drift vs Deliberate Modification: くなる vs くする
Just as nouns contrast になる with にする, い-adjectives contrast natural drift with intentional human action:
- Natural transition (〜くなる): The change happens on its own:
- 部屋が明るくなりました: “The room became bright.” (e.g. morning sun rose).
- Intentional adjustment (〜くする): Someone deliberately changes the state:
- 部屋を明るくしました: “I brightened the room.” (e.g. I turned on the lights).
In Dialogue
- Liam
外がずいぶん暗くなってきましたね。
It has gotten quite dark outside, hasn't it?
Hana雨が降りそうですね。急いで帰りましょう！
Looks like it might rain. Let's hurry home!
Quick Check
Select the correct phrase to say: ‘The weather became good (improved).’ ({いい} = good).