だ/です

The copula da/desu
だ and です are one and the same as far as meaning is concerned. Both serve as the verb "to be," but だ is informal while です is formal (for more on Japanese levels of politeness see 動詞の変化). The copula だ/です differs from ある/あります and いる/います which also mean "to be" in that while ある/あります and いる/います convey existence, だ/です equates something to something else. Here are some examples:

                                   ほん
あのテーブルに本があります
There is a book on that table.
なかむら               にわ
中村さんは庭にいます
Mrs. Nakamura is in the garden.

-------------------- Compare the above two sentences with the following: --------------------

          ひと      なかむら
あの人は中村さんです

That person is Mrs. Nakamura.

The Conjugation

The conjugation of だ/です is highly irregular but memorizing its various conjugations early is a good idea since it is so commonly used. As with memorization of verb and adjective conjugations, its best to start with rote memorization followed with application of the conjugations in actual sentences. Begin by reviewing the following chart taking mental note of patterns you see along the way. Then write them down while reviewing the chart. Try to work your way toward being able to write the chart from memory as quickly as possible so that any given tense will instantly spring forth the correct conjugation in your mind. This will help as you formulate sentences during conversation.

Informal (Common 普段)
Present Affirmative is/are
*ではない Present Negative is not/are not
だった Past Affirmative was/were
*ではなかった Past Negative was not/were not
だろう Tentative is probably/are probably
 
Formal (Polite 丁寧)
です Present Affirmative is/are
*ではありません Present Negative is not/are not
でした Past Affirmative was/were
*ではありませんでした Past Negative was not/were not
でしょう Tentative is probably/are probably
 
Conditional and Conjunctive
だったら Conditional if [subject] is/was
*ではなかったら Negative Conditional if [subject] is not/was not
Conjunctive is/are ... and/so
*ではなくて Negative Conjunctive is not/are not ... and/so
 
*a more colloquial form of では is じゃ (じゃありません=ではありません)

You'll notice above that each informal conjugation (aside from the conditional and conjunctive) have a corresponding formal (or polite) conjugation. So だ is to です as だった is to でした, ではない is to ではありません, ではなかった is to ではありませんでした, and だろう is to でしょう.  These pairs have the same tense but which of the pairs to use depends on the level of politeness in the sentence.  Generally, informal is used in everyday speech in Japan among friends, family and close coworkers.  Formal would be used in every other situation except the rare situations in which humble or super polite forms would be used (more on this in the verb section). You will also notice that there is no distinction between singular and plural usage.

Some Example Sentences

Here are some example sentences using the above conjugations of だ/です.  Note that there is no conjugation for future tense.  In Japanese the present tense is used for future tense and, when it is not already known by the listener, the future date or time is referenced by the speaker.  Often the tentative form is used when referring to the future.**

Informal Formal
彼は泳者だ。
[kare wa eisha da.]
He is a swimmer.
彼は泳者です。
[kare wa eisha desu.]
He is a swimmer.
彼は泳者ではない。
[kare wa eisha dewa nai.]
He is not a swimmer.
彼は泳者ではありません。
[kare wa eisha dewa arimasen.]
He is not a swimmer.
彼は泳者だった。
[kare wa eisha datta.]
He was a swimmer.
彼は泳者でした。
[kare wa eisha deshita.]
He was a swimmer.
彼は泳者ではなかった。
[kare wa eisha dewa nakatta.]
He was not a swimmer.
彼は泳者ではありませんでした。
[kare wa eisha dewa arimasen deshita.]
He was not a swimmer.
彼は泳者だろう。
[kare wa eisha darou.]
He is probably a swimmer.
彼は泳者でしょう。
[kare wa eisha deshou.]
He is probably a swimmer.
彼は泳者だったら元気だろう。
[kare wa eisha dattara genki darou.]
If he is a swimmer, he is probably healthy.
彼は泳者だったら元気でしょう。
[kare wa eisha dattara genki deshou.]
If he is a swimmer, he is probably healthy.
彼は泳者で上手に泳げる。
[kare wa eisha de jouzu ni oyogeru.]
He is a swimmer, so he swims well.
彼は泳者で上手に泳げます。
[kare wa eisha de jouzu ni oyogemasu.]
He is a swimmer, so he swims well.
彼は明日もまだ泳者だろう。**
[kare wa ashita mo mada eisha darou.]
He'll probably still be a swimmer tomorrow.
彼は明日もまだ泳者でしょう。**
[kare wa ashita mo mada eisha deshou.]
He'll probably still be a swimmer tomorrow.

There are many applications of だ/です so it's important to have a good handle on its conjugation as soon as possible.  In addition to equating a subject to an object, it is used to determine the tense of -な adjectives, and the level of politeness for both -な and -い adjectives. It can also be used on occasion to replace certain predicate verbs as in the example: 僕は寿司だ。(I'll have sushi.) in response to the question: 何にしますか? (What will you have?).  If you are just starting out learning Japanese don't worry too much about understanding all the applications of だ/です.  It is enough for now to simply familiarize yourself with its conjugation and learn its various applications as you move forward.

ホーム  平仮名と片仮名  日本語の名詞  日本語の助詞  だ/です
ある/ いる  形容詞の変化  動詞の変化  漢字辞典  日本語クイズ

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