Using い-Adjective くForm for Adverbs

    • Adjective
    • Adverb
    The く form is sometimes referred to as the “adverbial form” of い-adjectives, because it can be used as an adverb! It can also be combined with the verbs なる and する to indicate a change of state.

    Table of Contents

    The Adverbial く Form

    The く form can change an い-adjective into an adverb. In other words, it tells us about how an action is done. Think of it like adding -ly to English adjectives (like quick) to form adverbs (like quickly). Let's see this in action.

    • 時間がなかったから、はやく食べました。
    • There was no time, so I ate quickly.

    When it comes to adverbs, Japanese is actually much more consistent than English.

    • 私はながく京都に住みました。
    • I lived in Kyoto for a long time.
      ( Literally: I lived in Kyoto longly. )

    This is a perfectly acceptable sentence in Japanese, but "longly" would be incorrect in English. Compared to Japanese, English adverbs are quite limited in their scope. We often have to use other structures (like the prepositional phrase "for a long time") to achieve the same adverbial meaning that a Japanese adverb like 長く has.

    In general, all い-adjectives can function as adverbs when they are in the く form.

    In Combination with する and なる to Indicate Change

    When we pair a く Form adverb with the verbs する and なる, things get even more interesting. In both cases, this indicates a change of state, but there's a twist. With する, we know that the change was caused by someone, whereas with なる, the change occurs on its own.

    First, let's take a look at an example sentence that uses する:

    • ペイントを使って、友子は部屋を明るくしました。
    • Using paint, Tomoko made her room brighter.
      ( Literally: Using paint, Tomoko did her room brightly. )

    In this sentence, it's clear who caused the action, right? Tomoko is the one who "did her room brightly." In English, we would use the comparative "-er" form of the adjective to show that the room changed from "bright" to "brighter." Japanese does not have such a comparative form for い-adjectives, so "do brightly" 明るくする is what we use instead.

    なる is used instead of する when the person who causes the change is not clear, or unimportant. Let's check out another example:

    • 子供達は大きくなっていた。
    • The kids have gotten bigger.
      ( Literally: The kids have become bigly. )

    As we know, kids grow up pretty quickly (too quickly, if you ask a sentimental parent). While most parents make sure their kids are well-fed, we can't really say is the parents who cause them to grow up, right? In cases like this, we attach なる to the adverbial form, for something like "become bigly." Again, because Japanese lacks a comparative "-er" structure, we use an adverb instead.

    Other Uses of the く Form

    Other Forms of い-Adjectives

    Check out the chart below to see how く form fits into the い-adjective paradigm. Click on other conjugations or forms to learn more about them!

    Form 日本語 English
    Stem Form
    く Form strongly
    て Form くて strong, (and)
    Present Tense Form is-strong
    Past Tense Form かった was-strong
    Negative Form くない is-not-strong
    Past Negative Form くなかった was-not-strong
    Conditional Form ければ if strong...
    Measurable Noun Form strength
    Subjective Noun Form strong point