です (desu) is a polite form used at the end of many Japanese sentences. In Portuguese, it can appear in translations as “é”, “está”, “sou”, or “são”, but it does not function as a “to be” verb that can be placed in any sentence. The role of です depends on the type of predicate that comes before it.
The practical rule is: use です mainly after nouns and な-adjectives in polite sentences. After い-adjectives, it adds politeness, while the adjective itself expresses and inflects the state. With verbs, the polite form usually ends in ます, not in です.
What does desu mean in Japanese?
です helps form a polite predicate. Compare three types of sentences:
- 田中さんは先生です。
Tanaka-san wa sensei desu.
Tanaka is a teacher. - この町は静かです。
Kono machi wa shizuka desu.
This town is quiet. - It's hot today.
It's hot today.
Today is hot.
In the first sentence, 先生 is a noun. In the second, 静か is a な-adjective. In the third, 暑い is an い-adjective: it already contains the idea of “being hot,” and です makes the sentence polite.
This difference avoids translating each part mechanically. To understand how the predicate organizes the sentence, see the guide on how to form sentences in japanese.
Desu is not a universal “to be” verb
Calling です a “to be” verb can help in an initial translation, but it creates errors when it becomes an absolute rule. It does not replace all uses of “ser” and “estar” in Portuguese, nor should it be added after any Japanese verb.
A verb in the polite form usually uses ます:
- Correct: I study Japanese every day.
Every day, I study Japanese.
I study Japanese every day. - Incorrect: 毎日、日本語を勉強するです。
There is also no one-to-one correspondence between “to be” and です. Existence, location, ongoing actions, and state changes use other structures. Therefore, it is worth learning first the difference between nouns, adjectives, and verbs in Japanese grammar for beginners.
Polite forms with nouns and な-adjectives
Japanese mainly distinguishes non-past and past. The non-past can describe the present, habits, or future situations; the context indicates the appropriate reading. The Irodori grammar table presents this opposition and separates nouns, adjectives, and verbs.
| Form | Polite form | Example with noun |
|---|---|---|
| Non-past affirmative | です | 今日は休みです。 Today is a day off. |
| Non-past negative | じゃないです じゃありません ではありません | 今日は休みじゃないです。 Today is not a day off. |
| Affirmative past | でした | Yesterday was a day off. Yesterday was a day off. |
| negative past | じゃなかったです じゃありませんでした ではありませんでした | Yesterday was not a day off. Yesterday was not a day off. |
ja is common in speech. dewa appears more in writing and in formal contexts. This does not make ではない “out of use”: the choice depends on the register and the structure. The initial material of Irodori confirms the negatives じゃないです and じゃありません and explains the preference of dewa in writing.
What is the difference between desu and da?
です belongs to the polite style; だ belongs to the plain style. だ is not just a short pronunciation of です. The switch changes the register of the sentence and must match the situation and the rest of the utterance.
| Form | Polite style | Plain style |
|---|---|---|
| Non-past affirmative | 学生です | student da |
| Non-past negative | student ja nai desu | student ja nai |
| Affirmative past | student deshita | student datta |
| negative past | I wasn't a student. | It wasn't a student. |
In informal conversations, the だ final can be omitted in certain sentences, especially short questions: Student? (“Are you a student?”). This doesn't mean that だ and です they are interchangeable in any context. The simple forms table from the Japan Foundation records だ／だった／じゃない／じゃなかった for nouns and な-adjectives.
How does desu work with い-adjectives?
い-adjectives inflect on their own. Don't simply transform です in でした. The change occurs in the adjective:
| Form | Form | Translation |
|---|---|---|
| Non-past affirmative | 高いです takai desu | It's expensive. |
| Non-past negative | 高くないです takakunai desu | It's not expensive. |
| Affirmative past | 高かったです takakatta desu | It was expensive. |
| negative past | 高くなかったです takakunakatta desu | It was not expensive. |
So, it was expensive is incorrect. To delve deeper into this inflection, see how to use adjectives in japanese.
How do you pronounce desu?
The reading is desu. In many varieties and speech situations, the final u vowel is weakened or devoiced, making the word sound close to “des”. This does not authorize forcibly dropping the sound in all situations. Region, age, speed, emphasis, and degree of formality can alter the pronunciation. The NINJAL explains the pronunciation variation in です・ます and notes regional and generational differences.
How to turn a sentence with desu into a question?
In the polite register, add か at the end:
田中さんは先生ですか。
Tanaka-san wa sensei desu ka.
Tanaka is a professor?
この町は静かですか。
Kono machi wa shizuka desu ka.
Is this city quiet?
In informal speech, intonation and other endings can form questions without か. The guide on how to ask questions in japanese explains the difference between polite and informal questions.
Common mistakes with desu
- Using it after a dictionary-form verb: prefer 行きます in the polite style, not 行くです.
- Making the past tense of an い adjective as it was expensive: the correct form is 高かったです.
- Treating だ as a polite abbreviation: it belongs to the simple style and can sound too direct in certain relationships.
- Stating that ではない is not used: the form remains valid; じゃない it is just more conversational.
- Always pronouncing “des”: the reduction of u varies; first preserve the rhythm and listen to speakers in different contexts.
Short dialogue with desu
A: 田中さんは先生ですか。
Tanaka-san wa sensei desu ka.
Tanaka is a professor?
B: いいえ、先生じゃありません。会社員です。
Iie, sensei ja arimasen. Kaishain desu.
No, he is not a teacher. He is a company employee.
A: 昨日も仕事でしたか。
Kinō mo shigoto deshita ka.
Was it also a workday yesterday?
B: いいえ、休みでした。
Iie, yasumi deshita.
No, it was a day off.
Exercise: choose the correct form
- “It was quiet yesterday”: 昨日は静か（です／でした）。
- “Today is not a holiday”: 今日は祝日（じゃないです／だった）。
- “It was expensive”: 高いでした／高かったです。
- “I'm going to Japan” in polite style: 日本へ行くです／日本へ行きます。
Answers: 1) でした, because the sentence is in the past; 2) じゃないです, polite negative in the non-past; 3) 高かったです, because the い adjective receives the inflection; 4) 日本へ行きます, because verbs normally use ます the polite style.
Common questions
What does desu mean in Japanese?
です (desu) marks a sentence as polite and helps form predicates with nouns and adjectives. The translation can be “is”, “are”, “am”, or “are”, but the exact meaning depends on the context and the element that comes before it.
Is desu the verb to be in Japanese?
Not universally. This translation can help in simple sentences, but です does not replace all uses of “to be” and “to be”. Japanese verbs typically use ます in the polite style, while nouns and adjectives follow their own patterns.
What is the difference between desu and da?
です belongs to the polite style; だ belongs to the plain style. They can occupy corresponding functions after nouns and な-adjectives, but the choice changes the register and the relationship with the interlocutor. だ is not just an abbreviation of です.
How to put desu in the past and negative?
With な nouns and adjectives, use でした in the affirmative past. For negation, common forms include じゃないです, じゃありません, and ではありません; in the negative past, use じゃなかったです, じゃありませんでした, or ではありませんでした.
Can I use desu after any verb?
No. A polite verb usually ends in ます: 行きます, for example. The construction 行くです is incorrect in standard Japanese. です can appear after some forms that already function as predicates, but it does not replace verb conjugation.
Next step: recognize the type of predicate
Before choosing です, だ or ます, identify whether the core of the sentence is a noun, a な adjective, an い adjective, or a verb. This simple decision avoids most mistakes and connects this topic to the word order in Japanese and to the particles that mark the function of groups.