40760
I noticed many i-adjectives ending with く. I need to know why that happens.

いつか、あなたは背が **高く** なるでしょう。
CC BY-SA 3.0
2016-11-08T22:54:40.990
40759
2016-11-09T00:43:33.533
17380
question
adjectives
Why does い become く?
Simply because that is how you use i-adjective.

i-adjectives

> 高 **い** -> tall  
>  高 **くない** -> not tall  
>  高 **くなる** -> become tall

na-adjectives

> すてき -> lovely  
>  すてき **じゃない** -> not lovely  
>  すてき **になる** -> become lovely
CC BY-SA 3.0
2016-11-08T23:29:29.523
40760
2016-11-08T23:29:29.523
18142
40759
answer
Specifically, what's happening is that you're going from the adjective form to
the adverb form. This can seem a bit weird when you think you're just trying
to make a negative form or something, but that's how it works - roughly
speaking, you're going from "takai" = "tall" to "takaku nai" = "not in a tall
fashion" = "not tall".

i-adjectives behave a bit more like verbs in their conjugations, while na-
adjectives behave a bit more like nouns, in that when you do stuff with an
i-adjective you directly mess around with the ending, while with na-adjectives
you leave the word untouched and just use particles and verbs to do all the
heavy lifting.
CC BY-SA 3.0
2016-11-09T00:32:52.437
40761
2016-11-09T00:32:52.437
16022
40759
answer
Basically, changing the い to a く turns the adjective into an adverb.

> [速]{はや} **い** = quick  
>  [速]{はや} **く** = quickly

As mentioned by [this
answer](https://japanese.stackexchange.com/a/40760/18582), this is also used
to make the negative form of い adjectives:

> [小]{ちい}さ **い** = small  
>  [小]{ちい}さ **くない** = not small
CC BY-SA 3.0
2016-11-09T00:43:33.533
40762
2016-11-09T00:43:33.533
2017-04-13T12:43:44.260
-1
18582
40759
answer