According to Jisho, 病気 is a noun meaning 'illness'. I recently read the sentence Aは病気です, which I took to mean "[Person] A is ill". My confusion lies in whether 病気 is properly an adjective, i.e. "sick/ill", or an abstract noun, i.e. "sickness".

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    – Eddie Kal
    Jan 26, 2022 at 18:53

2 Answers 2


病気 is a noun, which describes a state. Because of this, it can be paired with the copula だ to describe the state of something or someone, just like in English.


A is sick.

です is just the polite form of だ. We could've used either.

Sometimes, it can be used as a "no-adjective", as in the following:


I called on my sick friend everyday.

However, what's really happening is that this の is not a particle but one of the alternant forms of だ, being な the other one. 病気の友人 means "a friend who is sick," which becomes "a sick friend." This doesn't translate as "friend of sickness."

Let's look at another example.


The medicine cured him of his illness.

Now this is the particle の.

Notice the word order: 病気の and の病気


Let's look at jisho.org's entry carefully. It says:


Noun, Noun which may take the genitive case particle 'no'

In other words, 病気 is a no-adjective as well as a noun; it can work like the English adjective "ill".

So-called の-adjectives - how does の *really* work?

As I understand it, the term “no-adjective” simply means “nouns which are typically translated to adjectives in English and other languages.” If we treat Japanese as a language in its own right, distinguishing them from nouns as different parts-of-speech is completely artificial.

の Adjectives | Japanese with Anime

The term "genitive case" refers to having a noun as modifying another word, usually a noun. That is, having a noun as adjective.

As these articles say, 病気 is still technically a (stative/descriptive) noun. But note that that English has similar noun usages, too, for example "person of credit" (= credible person), "man of courage" (= courageous man). So you may think the normal Japanese way of saying "ill person" happens to be closer to something like "person of illness". Aは病気だ is "A is of illness" rather than "A is illness", just like Aはフランスだ means "A is in France" rather than "A is France".

  • Definitely appreciate your statement, "If we treat Japanese as a language in its own right, distinguishing them from nouns as different parts-of-speech is completely artificial." I think many of the questions we field here at JSE are ultimately arising because the English-language textbooks that describe various Japanese-language features don't do a very good job of describing Japanese as Japanese, and learners get bogged down in "Japanese as English", which doesn't work very well. Jan 26, 2022 at 1:21
  • @EiríkrÚtlendi That's not my own words :)
    – naruto
    Jan 26, 2022 at 1:26
  • 1
    ha! Well, still, good of you to include that portion. I see that the quoted text appears with a yellow background on mobile, making it more immediately obvious that it's a quote -- but on my laptop, there is no background color, making it more visibly ambiguous. I confess I very much dislike the style direction the SE developers have taken... Jan 26, 2022 at 9:58
  • It seems to me though the ability to function as a predicative nominal is not restricted to no-adjectives. Can't most, if not all, nouns be used this way? Neither フランス nor 日本 is defined as a no-adjective in WWWJDIC.
    – Eddie Kal
    Jan 27, 2022 at 7:48
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    @EddieKal 私はフランス料理だ is an うなぎ文 that must be said after some context has been set up, but 私は病気だ makes sense on its own. So I think 病気, 永遠, 突然 and so on do have some adjective-like quality ordinary nouns do not have.
    – naruto
    Jan 28, 2022 at 1:40

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