The Copula Verb だ
断定助動詞（コピュラ）の「だ」
The simplest sentence structure in most languages is “X is Y.” This sentence structure in grammar is called either “copular sentence” or “noun-predicate” sentence (名詞述語文). The Japanese copula verb is used a lot, so just learning about this single grammar item will get you making sentences in no time. First, let’s cover some basic grammar terminology to make reading this chapter a lot easier.
- Subject: The person/thing that performs the action or exhibits the description found in the predicate.
- Predicate: The part of a sentence that makes a statement about the subject.
- Copula: A word used to link the subject and predicate of a sentence.
- Noun: In its most basic definition, a word that refers to a person, place, thing, event, substance, or quality.
- Auxiliary: An ending that helps construct verbal conjugations.
- Plain Speech: Refers to the entire plain speech register in Japanese grammar.
- Plain Style: Is the plain speech rendition of any given phrase.
- Plain Form The basic form of any given phrase.
In English, the copula verb is “to be,” and it manifests itself in various forms such as “is,” “are,” “was,” etc.
i. The dog is a German shepherd.
ii. My husband is a banker.
iii. Apples are fruits.
iv. It was a fossil.
v. A bat is not a bird.
Similarly, the Japanese copula verb だ has its own various forms. Naturally, Japanese does not conjugate for the same things as English does, and this is especially true in terms of tense.
In English, there are three tenses: past, present, and future. As their names suggest, the past tense refers to an event/state which occurred in the past, the present tense refers to a current event/state, and the future tense refers to an event/state that has yet to realize. Affirmation is positively stating that something is so. Negation is the opposite of affirmation as it is the means of rejecting a premise.
Japanese only has two tenses: non-past and past, with the non-past tense encompasses both the English present tense and future tense. Though there are many distinct ways in which tense differ between the two languages, the contexts shown in the basic sentences of this lesson, in large part, avoid going into too much depth in this regard, as our main purpose is learning how だ means “to be.”
Lastly, before delving into how the copula verb だ works, as this is the first conjugatable part of speech to be covered, that means this will be your first exposure to the Japanese base-ending conjugation system, which was mentioned in Lesson 0. IMABI takes a firm stance on the necessity of understanding Japanese conjugation for how it is, and so whether you remember the names of the bases now or later, it is crucial that you know how conjugating work.
The terminology to be used throughout this lesson as well as in any discussion on how to conjugate which are pertinent to the forms discussed are as follows:
- Base: One of the six forms that a conjugable part of speech (verb, adjective, auxiliary verb, etc.) may take which is then followed by endings (auxiliaries, etc.).
- Terminal/Predicative Form: Known in Japanese as the 終止形, it marks the end of a complete sentence/the predicate.
- Attributive Form: Known in Japanese as the 連体形, it is used to make a verb, adjective, etc. into a modifier that goes directly before a noun.
- Basic Form: The basic form of any given phrase, in other words, is utilized in plain speech as well as in many grammatical circumstances. The basic form encompasses both the predicative and the attributive forms in the context of verbs and adjectives.
- Continuative Form: Known in Japanese as the 連用形, it is used with endings pertaining to actions (being) carried out.
The Copula Verb だ
The basic form of the Japanese copula verb is だ1. When directly translated into English, it may be stand for “to be,” “is,” “am,” “are,” “will be,” etc. Because the verb of a Japanese sentence must come at the end of a sentence in its predicative form (終止形), one must NEVER render “X is Y” as “XだY.” To create a valid sentence in Japanese with だ, the basic pattern is instead XはYだ2.
The Non-Past Tense
非過去形
The non-past/basic form (非過去形・基本形) of the copula verb だ encompasses both the present and future tense forms3 as well as the base form of the English copula verb “to be.”
| Form | English | Japanese |
| Base | to be | だ |
| Present Tense | am/are/is | だ |
| Future Tense | will be | だ |
In the example sentences that follow, we will see how XはYだ can stand for the present tense and the future tense. In doing so, だ in its “predicative form,” as it is at the end of the sentence and constitutes as the main clause (主節) of the sentence. Thankfully, no other clauses but the main clause are involved here.
■Non-Past: Present
1. あれは寺だ。
That over there is a Buddhist temple.
2. それは嘘だ。
That is a lie.
3. これは事実だ。
This is the truth.
4. あの新人は大学生だ。
That newcomer/recruit is a college student.
5. あの人は韓国人だ。
That person is Korean.
6. 書道は芸術だ。
Calligraphy is art.
7. 彼はバカだ。
He’s an idiot.
One nuance that can be noted from these examples without being too specific is that だ is very direct. In general, Japanese speakers are more likely to be this direct when writing more so than when they are speaking. Especially when talking about interpersonal things, in conversation where one might utilize Ex. 4 and Ex. 5, it would be more natural to drop だ altogether (see below).
■Non-Past: Future
As can be deduced from the examples, English also shows fluctuation between “is” and “will be” in certain contexts, especially when referencing established dates.
8. 元日は月曜日だ。
New Year’s Day [is/will be] on Monday.
9. 開始日は明日だ。
The start date [is/will] be tomorrow.
10. パーティーは夜だ。
The party [is/will be] at night.
Omitting Xは
Omitting Xは from the pattern XはYだ is incredibly common. This is especially the case when the subject of the English sentence is rendered as the meaningless use of the word “it.”
11. 明日だ。
[It’s/it’ll be] tomorrow.
12. あ、猫だ！
Ah, (it’s) a cat!
13. 時間だ。
Jikan da.
(It’s) time.
Omitting だ
As has been stated, the copula だ itself may be dropped from the pattern XはY to avoid sounding too direct, even in the context of conversation had in plain speech. The presence of だ often creates a direct, firm, at at times, a more masculine tone.
Another reason for omitting だ is when making an exclamation. In such sentences, even the copula verb is English is usually dropped.
14. あ、ピカチュウ（だ）！
Ah, (it’s) (a) Pikachu!
15. 開始（だ）！
Start!
16. 動物園（だ）！
(It’s) [a/the] zoo!
17. 引き分け（だ）！
(It’s a) draw!
18. あ、カワウソ（だ）！
Ah, (it’s) an otter!
The Past Tense
過去形
The past tense form (過去形) of the copula verb だ is だった, which translates into English as “was/were.” The auxiliary verb used in this conjugation that indicates the past tense is ～た, which goes after the continuative form (連用形). Remember that this “continuative form” pertains to things (being) carried out, which includes situations that are already over.
| Form | Conjugation | Base | Auxiliary |
| Non-Past | だ | だ (predicative) | n/a |
| Past | だった | だっ (continuative) | ～た |
19. さっきの言語はフランス語だった。
The language just now was French.
20. ここは学校だった。
This here was a school.
21. 正解はAだった。
The correct answer was A.
22. 昨日は水曜日だった。
Yesterday was Wednesday.
23. 彼は子供だった。
He was a child.
Grammar Note: The past tense form need not always be interpreted literally. Ex. 23 could also be used to confirm that a child present is, in fact, a child.
The Negative Form
否定形
The negative (non-past) form (否定形) of the copula verb だ is ではない, which translates into English as “is/am/are not.” Here, we see the continuative form (で) used with the negative auxiliary ～ない (not) is not the same continuative form used for its past tense form (だっ). Instead, this secondary continuative form で may be thought of as an “adverbial form” in which the noun-predicate that is marked by だ functions as an adverb onto the negative ending. In other words, the predicate describes how X is not Y.
In Japanese grammar, the ending ～ない, contrary to its English counterpart “not,” functions as an auxiliary adjective as opposed to an auxiliary verb. Another peculiarity about this structure is the appearance of は (see below) in between the adverbial form で and the auxiliary adjective ～ない.
| Form | Conjugation | Base | Auxiliary |
| Non-Past | だ | だ (predicative) | n/a |
| Past | だった | だっ (continuative) | ～た |
| Negative | ではない じゃない4 | で (adverbial) | ～ない |
As for why the particle は is used, it appears in this structure to add emphasis to X not being Y, which in turn helps set a contrastive tone. You may also have noticed the inclusion of the form じゃない (isn’t), which is the casual contraction of ではない. This casual form is especially common in conversation.
24. これはペンではない。
This is not a pen.
25. コウモリは鳥ではない。
Bats are not birds.
26. クジラは魚ではない。
Whales are not fish.
27. 月は惑星じゃない。
The moon isn’t a planet.
28. あれは犬じゃない。
That isn’t a dog.
29. これはお茶じゃない。
This isn’t tea.
ではない vs でない vs じゃない vs じゃあない
As for whether は is absolutely necessary in ではない to make a grammatically correct sentence, especially given that じゃない has less of a contrastive tone to it than ではない, the short answer is no.
In fact, based on the understanding that は imposes a contrasting tone means that でない ought to be viewed as the most basic, negative form of the copula. Yet, in both the written language and the spoken language, でない is excessively rare when used as the predicative form (終止形), as it is deemed too stiff and direct. That is not to say a speaker will never purposely sound this way, but Japanese speakers tend to avoid such a speech style.
Contrary to this, though, でない becomes the default choice when used as the attributive form (連体形)5, with ではない becoming unnatural if a highly contrastive tone is not warranted. As for how one might reinsert the contrastive tone to じゃない, that would be done by rendering it as じゃあない, which you are more likely to hear spoken rather than see written down, but with a rather macho tone.
30a. そうでない星
30b. そうではない星
30a. A star that is not like that
30b. A star that is not like that
31. あの星はそうではない。
That star is not like that.
32. あの物体は星じゃあない。
That object is no~t a star.
The Negative-Past Form
過去の否定形
The negative-past form (過去の否定形) of the copula verb だ is ではなかった, which translates into English as “was not/were not.” It may also be rendered in casual speech as じゃなかった, which translates into English as “wasn’t/weren’t.”
This structure utilizes the past tense conjugation of the auxiliary adjective ～ない, which is ～なかった. Although we will not study how adjectives are conjugated in general until Lesson 14, the mechanics involved are no different: ～た follows the continuative form. Therefore, the continuative form of ～ない must be ～なかっ.
| Form | Conjugation | Base | Auxiliar(ies) |
| Non-Past | だ | だ (predicative) | n/a |
| Past | だった | だっ (continuative) | ～た |
| Negative | ではない じゃない4 | で (adverbial) | ～ない |
| Negative-Past | ではなかった じゃなかった4 | ではなかっ (continuative) | ～ない＋～た |
Note that the basis for why は appears in this structure is the same as with its non-past tense rendition discussed previously.
33. その代表は彼女ではなかった。
That representative was not her.
34. 原因は煙草ではなかった。
The cause was not tobacco.
35. あれは模擬試験ではなかった。
That was not a mock exam.
36. 彼は僕の友達じゃなかった。
He wasn’t my friend.
37. あれは水じゃなかった。
That wasn’t water.
38. それは嘘じゃなかった。
That wasn’t a lie.
In Conclusion 最後に…
By learning the basic sentence structure XはYだ along with its most basic conjugations, we have already established a firm foundation for understanding how things conjugate in Japanese in general. In this lesson that follows, we will interject politeness marking in the discourse.
- Contrary to the general norm in second-language Japanese education, the polite forms of the copula are to be discussed next as opposed to being mentioned first. The reasoning for this is that while it is true that speech register – the level of politeness – affects every aspect of phrasing in the language, plain speech constitutes the basic form of any and all grammatical structures. In fact, polite speech requires that one add politeness markers to those very plain speech structures. By starting with the basic, plain speech conjugations of the copula verb, we are truly starting at ground zero. ↩︎
- Technically, the particle が does mark the subject of all clauses, including these basic noun-predicates involving the copula verb, regardless of whether it is actually spoken. However, differentiating between XがYだ and XはYだ requires a deep understanding of the particles が and は themselves along with other grammatical concepts such as deep-sentence structures vs. overt sentence structures, which would all detract from learning how to say “X is Y” in a basic level understanding of Japanese. As such, we will hold off on learning about those particles until Lessons 12-13. ↩︎
- “Tense” in Japanese is 時制, whereas ～形 means “form.” When referring to which tense something is being used for, the terms 現在形 (present tense form) and 未来形 (future tense form) are used just as much as 非過去形 (non-past tense form) so as to better relate how a Japanese sentence ought to be interpreted back into English. ↩︎
- Casual speech is a subset of plain speech. Speakers are more likely to use casual forms in conversation rather than in writing, whereas plain speech itself more broadly refers to the basic grammatical rendition of grammar points and sentences, being stripped of any politeness markers. Casual forms tend to be contractions or dialectal, slangish, as well as informal derivatives of a common, basic rendition that would constitute as the ‘plain speech’ form. In formal writing, ではない is used as opposed to じゃない, as the latter is seen as an informal contraction; however, in the spoken language, while じゃない is still informal, ではない takes on a more contrastive tone. Additionally, じゃない itself has an even more informal variant: じゃねー, which is often seen in coarse men’s speech. ↩︎
- The attributive form, as stated in its definition, enables conjugatable parts of speech to directly modify nominal phrases. However, as understanding how this truly works requires knowing how adjectival grammar and subordinate clauses work in Japanese, this will be the only mention of it in this lesson. ↩︎