So recently I came across these two answers to two very interesting questions, and related: one and two.

Both mention the following form:

(連用形{れんようけい} of something) + (optional 係助詞{かかりじょし}) + (ない or ある)

I do understand the difference in nuance (between 悪くない vs 悪くはない, for example), but I don't understand why it is acceptable grammatically.

Correct me if I'm wrong but は here emphasizes and contrasts 悪く, but what is 悪く, really? It translates into 'badly', which is an adverb that is usually supposed to modify a verb or connect to another adjective. With that logic in mind, the overall (literal) translation would be 'There is no badly', which is just weird.

I feel like I'm missing something about conjugations they don't usually teach you in textbook Japanese, which is why I'm after the historical reasoning behind it.

  • 1
    These ある or ない here mean "to be so" rather than "to exits". So it'd be "is not badly so".
    – user4092
    Commented Aug 21, 2017 at 4:28

1 Answer 1


As the other answers say, 悪く is a 連用形 ("continuative form") of 悪い. This form can work as an adverb on its own, but here it's merely a form that precedes ない. As a rule, whenever you want to use ない with an i-adjective, you must use this 連用形 form. 悪くない just means "not bad".

For convenience, in some beginner materials, 悪くない is often described simply as "negative-form / nai-form of i-adjectives," and 悪く as "adverb form", as if they were totally different. You may be already familiar with these terms. However, 悪くない is actually two words (i.e., the 連用形 of an adjective followed by an auxiliary ない). That's why the contrast marker は can be inserted between 悪く and ない. As you learn Japanese grammar (especially using monolingual resources), you'll see the term 連用形 more and more often.

Unfortunately, one verb/adjective can have up to two 連用形. The 連用形 of 悪い are 悪かっ and 悪く (see this chart), and the 連用形 of 書く are 書き and 書い. This is not a big problem for native Japanese speakers, but can be a huge problem for learners. I think this is one of the reasons the word 連用形 is not popular for beginners. See also: Does "te-form" of a verb always include て/で? Why?.

  • Thanks @naruto! I don't get it though, why can 連用形 as a form take a particle? What meaning does it have? は here seems to contrast 悪く but what is the meaning of 悪く by itself? Is it really just 'badly'?
    – xTCx
    Commented Aug 21, 2017 at 8:15
  • 2
    @xTCx You have to stop thinking each form has a distinct meaning, although some forms have distinct meanings on its own. 連用形 was named after the fact that it is followed by various particles with various meanings, like て, た, ます, etc. It's just a grammatical rule. Beginners start learning Japanese "forms" that can be used right away, such as te-form, ta-form and masu-form. But they are all actually 連用形 followed by another particle, according to monolingual dictionaries or 学校文法.
    – naruto
    Commented Aug 21, 2017 at 8:36
  • when you put it like that it makes much more sense! I also read the links you provided and they do explain it quite nicely. I think this transition between textbook Japanese and 国語文法 is quite a difficult one.
    – xTCx
    Commented Aug 21, 2017 at 8:59

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