The Copula Verb だ
断定助動詞（コピュラ）「だ」

The simplest sentence structure in most languages is “X is Y.” In grammar, this is known as a “copular sentence” or a “noun-predicate sentence” (名詞述語文). In Japanese, the copula verb is highly versatile and frequently used. By mastering this single grammar point, you will be able to start forming sentences right away.

Before we begin, to help you navigate this chapter more easily, let’s first cover some basic grammar terminology.

• 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.

Forms of “To Be” in English

In English, the copula verb is “to be,” and it manifests itself in various forms such as “am,” “are,” “is,” “was, “were,” etc. 

i. The dog is a German shepherd.
ii. I am a banker.
iii. That was a fruit.
iv. They were not fossils.
v. Bats are not birds.

Similarly, the Japanese copula verb だ also has various forms, but its conjugations differ significantly from those in English. This is especially evident when it comes to tense.

Tense

In English, there are three primary tenses: 

1. Past tense: Refers to an event or state that occurred in the past.
2. Present tense: Refers to a current event or state.
3. Future tense: Refers to an event or state that has yet to occur.

While Japanese does conjugate for tense, it does so very differently. Overall, tense distinctions are more context-dependent. This can largely be attributed to how Japanese only has two primary tenses:

1. Non-past tense: Refers to an ongoing event or state or one that has yet to occur.
2. Past tense: Refers to an event or state that occurred in the past.

Affirmation and Negation

Another dynamic that affects how conjugation differs between English and Japanese is how affirmation and negation are handled.

• Affirmative sentence: A sentence that positively states that the premise (predicate) is the case.
• Negative sentence: A sentence that rejects the premise (predicate).

Introducing Japanese Conjugation w/だ

The copula verb だ will be your first encounter with a conjugatable part of speech and Japanese, and what you will learn in this lesson will serve as an introduction to how Japanese’s base-ending conjugation system works.

The following terms will be used throughout this lesson and in future discussions on how to conjugate:

• 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 translated into English, it represents “to be,” “is,” “am,” “are,” as well as “will be” depending on the context.

In Japanese, the verb must appear at the end of the sentence in its predicative form (終止形). As a result, “X is Y” cannot be rendered as “XだY.” To create a grammatically sound sentence using だ, the correct pattern is XはYだ².

1. コーヒーは飲み物だ。
Coffee is a drink.

Here, we see that the structure starts off with the subject (X) marked as the topic of discussion by the particle は (→ Lesson 13), followed by the predicate (Y). Predicates must be composed of a part of speech that can conjugate in Japanese, and to accomplish this, だ attaches to the noun that stands for Y.

The Non-Past Tense　
非過去形 

The non-past (非過去形), also known as the basic form (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

While the non-past tense in Japanese encompasses both the present tense and the future tense, it is not the case that both interpretations will make sense in any given context. The context will definitely make the interpretation obvious, with time phrases such as “tomorrow” being important for deciphering. As for determining how だ should be interpreted, though, its non-past form (Exs. 2-8) is usually interpreted as being in the present tense, with its future tense (Exs. 9-12) interpretation limited to specific contexts.

In these examples, だ is in its “predicative form,” appearing at the end of the sentence and constitutes the main clause (主節) of the sentence.

Non-Past = Present Tense

2. あれは寺だ。
That over there is a Buddhist temple.

3. それは嘘だ。
That is a lie.

4. これは事実だ。
This is the truth.

5. あの新人は大学生だ。
That newcomer is a college student.

6. あの人は韓国人だ。
That person is Korean.

7. 書道は芸術だ。
Calligraphy is art.

8. 彼はバカだ。
He is an idiot.

One notable observation from these examples is that だ conveys a very direct tone. While this level of directness is more common in written Japanese, it is less frequently heard in spoken conversation, particularly when discussing interpersonal matters. In fact, in conversations where one might use examples like Ex. 5 or Ex. 6, it is often more natural to omit だ altogether; this subtle adjustment reflects the more implicit and less direct style of spoken Japanese (see below).

Non-Past = Future Tense

As can be deduced from these examples, English also exhibits fluctuation between “is” and “will be” in the same contexts in which だ can be viewed as either or in its non-past form, particularly when referring to established dates, which are incidentally also “future” events. This parallels how だ encompasses both the present and future tense in Japanese.

9. 元日は月曜日だ。
New Year’s Day [is/will be] on Monday.

10. 開始日は明日だ。
The start date [is/will be] tomorrow.

11. パーティーは夜だ。
The party [is/will be] at night.

One situation in which the future tense interpretation of だ is obligatory is when a time phrase that only pertains to the future is used.

12. 明日は雨だ。
It will rain tomorrow.⁴

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 corresponding English sentence is the often meaningless pronoun “it.”

13. 明日だ。
[It’s/it’ll be] tomorrow.

14. あ、猫だ！
Ah, (it’s) a cat!

15. 時間だ。
(It’s) time.

In each of these sentences, “it” functions as a placeholder for the grammatical subject. As Japanese does not necessitate that X always be overtly present in a sentence, no such word exists for that same function. Instead, if X is to be used in Japanese, it must be a regular noun or pronoun. Luckily, if “it” appears in the same capacity as seen in Exs. 13-15 in English, it will correspond to nothing in Japanese.

Omitting だ in Exclamations

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, and at at times, a more masculine tone.

Another common context for omitting だ is in exclamatory sentences. In such cases, even the copula verb is often omitted in English.

16. あ、ピカチュウ（だ）！
Ah, (it’s) (a) Pikachu!

17. 開始（だ）！
Start!

18. 動物園（だ）！
(It’s) [a/the] zoo!

19. 引き分け（だ）！
(It’s a) draw!

20. あ、カワウソ（だ）！
Ah, (it’s) an otter!

The Past Tense　
過去形

The past tense form (過去形) is created by adding the auxiliary verb ～た to the continuative form (連用形) of a conjugatable part of speech. In the case of the copula verb だ, its continuative form is だっ, resulting in だった. The continuative form is used in this construction because of how it 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

21. さっきの言語はフランス語だった。
The language just now was French.

22. ここは学校だった。
This here was a school.

23. 正解はAだった。
The correct answer was A.

24. 昨日は水曜日だった。
Yesterday was Wednesday.

25. 彼は子供だった。
He was 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.”

In this structure:

1. The continuative form of だ becomes で.
2. The negative auxiliary ～ない (not) is added, forming ではない.

It is important to note that で here differs from the continuative form だっ used for the past tense. Instead, で can be thought of as an adverbial form, where the noun-predicate marked by だ acts as an adverb modifying the negative ending. Essentially, this construction describes how X is not Y.

More grammatical peculiarities that can be noted from this structure include:

1. ～ない as an Auxiliary Adjective:
   Unlike its English counterpart “not,” which functions as an auxiliary verb, ～ない operates as an auxiliary adjective in Japanese grammar.
2. The Role of the Particle は:
   The particle は appears between the adverbial continuative form で and the auxiliary adjective ～ない. This emphasizes the negative aspect of the sentence and sets a contrastive tone, distinguishing the statement from other possibilities.

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5	で (adverbial)	～ない

26. これはペンではない。
This is not a pen.

27. コウモリは鳥ではない。
Bats are not birds.

28. クジラは魚ではない。
Whales are not fish.

The Casual Form じゃない

You may have noticed the inclusion of the casual form じゃない, which corresponds to “isn’t/aren’t” in English, in the chart above. This is the casual contraction of ではない, and it is especially common in conversation and informal contexts.

29. 月は惑星じゃない。
The moon isn’t a planet.

30. あれは犬じゃない。
That isn’t a dog.

31. 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 than ではない, the short answer is no.

In fact, based on the understanding that は imposes a contrasting tone, 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 in the predicative form (終止形), as it is deemed too stiff and direct. That is not to say a speaker will never intentionally go for this effect, such a speech style is generally avoided.

Contrary to this, でない becomes the default choice when used in the attributive form (連体形)⁶, with ではない becoming unnatural unless a highly contrastive tone is 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.

32a. そうでない星
32b. そうではない星
32a. A star that is not like that
32b. A star that is not like that

33. あの星はそうではない。
That star is not like that.

34. 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.” In casual speech, this is often shortened to 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. While we will delve into adjective conjugation in detail in Lesson 14, the mechanics here are straightforward:

• ～た is attached to the continuative form of ～ない, which is ～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	で (adverbial)	～ない
Negative-Past	ではなかった じゃなかった	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.

35. その代表は彼女ではなかった。
That representative was not her.

36. 原因は煙草ではなかった。
The cause was not tobacco.

37. あれは模擬試験ではなかった。
That was not a mock exam.

38. 彼は僕の友達じゃなかった。
He wasn’t my friend.

39. あれは水じゃなかった。
That wasn’t water.

40. それは嘘じゃなかった。
That wasn’t a lie.

1. 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. ↩︎
2. 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” at a basic understanding. These particles are covered in Lessons 12-13. ↩︎
3. “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.   ↩︎
4. While the English translation uses the verb “to rain,” the Japanese sentence literally translates as “As for tomorrow, there will be rain.” ↩︎
5. 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. ↩︎
6. 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. ↩︎