い-Adjective くない (Negative Form)

    • Adjective
    Adding 〜くない to the end of an い-adjective makes it negative, kind of like how "not" functions in English.

    Table of Contents

    The Basics

    〜くない is the negative form of い-adjectives. So while 難し means "is-difficult," 難しくない means "is-not-difficult." Notice that both of these end in the present tense 〜い ending, a feature that they both share.

    Forming 〜くない

    To form 〜くない, you simply drop the 〜い ending from an い-adjective and replace it with 〜く, putting it into the くform. This allows the い-adjective to stick to another word or element, in this case, 〜ない.

    Let’s see how this works with an actual adjective:

    難し + く + ない = 難しくない

    It certainly 難しくない (is not difficult), right?

    This works for all い-adjectives, without exception🎉 Bear in mind that the stem form of いい is よ, so the negative form of いい is よくない.

    〜くない in the Past

    〜くない can also be used in the past tense, or the 〜かった form. To do so, you simply change the final 〜い to 〜かった, just like you do with positive い-adjectives.

    難しくな = 難しくなかった

    That 難しくなかった (was not difficult) either, was it?

    Politeness

    Politeness in Japanese is marked at the end of a sentence with forms like です and 〜ます. If you have a sentence that ends in an い-adjective, you can level-up your politeness using these forms.

    One option is to add です after the negative suffix 〜ない. This style is common in polite conversation:

    • 難しくないです
    • is not difficult (formal)

    Alternatively, you can switch out 〜ないです for the more formal ending, 〜ありません. This option feels a little bit too stiff for most spoken situations, so it tends to be used more commonly in writing.

    • 難しくありません
    • is not difficult (formal)

    Sentence Structure

    Like positive い-adjectives, negative い-adjectives can appear either at the end of a sentence or immediately before a noun.

    At the End of a Sentence

    When a negative い-adjective appears at the end of the sentence, it describes the subject of the sentence.

    • あの芸人は面白くない
    • That comedian is not funny.

    In this case, the negative い-adjective 面白くない (is-not-funny) is describing the subject あの芸人 (that comedian).

    Immediately Before a Noun

    Negative い-adjectives can appear directly before a noun. These modified nouns can appear anywhere that unmodified nouns can appear, such as the subject or object of the sentence.

    • 面白くない芸人が、苦くないコーヒーを作った。
    • A not-funny comedian made not-bitter coffee.

    Here, 面白くない芸人 is the subject and 苦くないコーヒー is the object.

    Beyond the Basics

    Splitting く Form and ない with Particle は for Contrast

    It's easy to think of 〜くない and 〜くありません as units, but remember that they are in fact two separate components: くform + a negative word. Because of this, they can be separated by the particle は to give a nuance of contrast.

    • おいしくない
    • not delicious (but…)
    • おいしくありません
    • not delicious (but…)

    Imagine that my friend is feeling a bit sick. I just so happen to have an amazing cold remedy tea, but the problem is, it tastes horrible. When offering it to her, I might say:

    • おいしくないけど、体にいいよ。
    • This isn't delicious, but it's good for you.

    By inserting particle は here, it creates the sense that whatever I say is going to be contrasted with something else. In this case, I contrast the taste (おいしくはない) with the health benefit (体にいい). For this reason, it’s quite common for 〜くはない to appear alongside "but" conjunctions, like が and けど. However, sometimes the contrast is implied rather than explicitly stated:

    • 悪くはないよ!
    • It's not bad (but…)

    You might use this when you want to say that something isn’t bad, but imply that it isn’t exactly good either, without stating it explicitly. In fact, after drinking that nasty healthy tea, this would be a great way for my friend to respond!

    Confirming Assumptions with 〜くない

    It is common to use 〜くない to ask questions that you think you know the answer to. This is similar to asking, "Isn’t it…?" in English. While the question form is negative, the speaker usually assumes that the actual answer is positive.

    • くない?
    • Isn't it cold?
    • くない?
    • Isn't it expensive?

    Common Mistakes

    Treating い-Adjectives like な-Adjectives

    Japanese has another type of adjective, called な-adjectives. Their grammar is more similar to Japanese nouns than to い-adjectives. For example, you can add 〜じゃない to form the negative form of な-adjectives.

    • その蚊は元気じゃない
    • That mosquito is not well.

    However, using じゃない to make an い-adjective negative is ungrammatical.

    • ❌そのハエはうるさいじゃない
    • ⭕そのハエはうるさくない
    • That fly is not noisy.

    Treating な-Adjectives like い-Adjectives

    It is also possible to mistake some な-adjectives for い-adjectives. For example, きれい (clean) is a な-adjective. However, it ends in い, so you could be forgiven for thinking it's an い-adjective.

    • ❌私の部屋はきれくない
    • ⭕私の部屋はきれいじゃない
    • My room is not clean.

    Luckily, there aren't so many な-adjectives ending in い. To distinguish them from い-adjectives, check their kanji version. Unlike い-adjectives, the final 〜い of these な-adjectives is not in hiragana. For example, the kanji for きれい is 綺麗, not 綺麗い. The only exception to this is 嫌い (to hate), which is a な-adjective in spite of the い hanging off the end. 🤷🏻‍♀️