~くなる vs ~になる

~くなる vs ~になる

Today’s Question

もう夏(なつ)ですね。もみじの はっぱは いまは みどり ですが、あきには ____。
もみじ = a maple (tree)

  1. あかい でしょう
  2. あかい です
  3. あかく  なります
  4. あかに なります

Today’s Grammar Point: ~く/~に なります

なります is the most common word that describes a change. Although なります can be used with many other words and have various meanings, the most basic meaning is “to become ~.”


  • [noun] + に + なります
  • [なadjective] + + なります
  • [いadjective stem] + + なります
    “いadjective stem” means “いadjective” minus the ending い

Examples with a noun

ジョンさんは えいごの せんせい なりました
John became a teacher of English.

もうすぐ 五時 なります
Soon it will be 5 o’clock.

わたしは ピアニスト なりたいです。
I want to be a pianist.

Examples with a なadjective

はやく げんき なってください。
Please get well soon.

ことしから てつづきが かんたん なりました
The procedure was been made simpler this year. (This year, the procedure became simpler.)

せいとが いえに かえって、学校は しずか なりました
Students went home and the school became quiet.

Examples with an いadjective

5時ごろから みせが いそがし なりました。(いそがし = busy)
The shop got busy from around 5 pm. (This suggests it wasn’t very busy until 5 pm.)

らいげつから このサイトが もっと おもしろ なります。(おもしろ = interesting)
This site will become more interesting from next month.

えいがを みて、メアリーさんは かなし なりました。(かなし = sad)
Mary watched the movie and felt sad.

When a colour changes

There are 6 colour words in Japanese which can be used as a noun as well as an いadjective by adding い afterwards. They are:

あか (red), あお (blue), しろ (white), くろ (black), きいろ (yellow) and ちゃいろ (brown).

When the colour of something changes to one of the above 6 colours, you have to think of how the change occurs.

If the change is natural and gradual, like leaves turning red or yellow, an いadjective is used, so the sentence should end in ~く なります.

If the change is mechanical, like turning a switch, we prefer using the noun form, so the sentence should end in ~に なります.


The maple leaves will turn red. (natural, gradual)
(✓)もみじの はっぱが あか なります
(✖)もみじの はっぱが あか なります

Emma blushed. (natural).
(✓)エマさんは あか なりました。
(✖)エマさんは あか なりました。

My mum’s hair has turned completely white (because of her age).
(✓)ははの かみは すっかり しろ なりました。
(✖)ははの かみは すっかり しろ なりました。

The traffic light changed red. (mechanical)
(✖)しんごうが あか なりました。
(✓)しんごうが あか なりました。

The new card has changed to black. (artificial)
(✖)あたらしいカードは くろ なりました。
(✓)あたらしいカードは くろ なりました。

Answer to Today’s question: c

The sentence says: “It is already summer. Maple leaves are green now but they _____ in autumn.”

Because it is talking about maple leaves, not any leaves, the blank should be filled with “turn red” or “become red.” You need to choose the verb with the meaning of “turn/become.” です/でしょう  do not have that meaning. The best answer is c. They turn “red” and this process is natural, gradual, so we prefer the いadjective, あかい, to the noun form あか (shown in the choice d).

Related post: 青い vs 青の

2 thoughts on “~くなる vs ~になる

  1. Reply
    青い vs 青の | EasyJapaneseE
    28 January 2023 at 4:02 pm

    […] With these 6 colours, you need to be careful if you are talking about something natural or something artificial/mechanical. For the difference between 赤くなる vs 赤になる, please read this post. […]

  2. Reply
    ふとい/ふとる/ふとっている/ふとくなる | EasyJapaneseE
    13 July 2021 at 2:49 pm

    […] Now if you want to describe a change, for things, we use 太くなる and for a person or an animal, we use 太る. (For explanation about [いadjective stem] + く + なる, please read this post.) […]

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