ですTo be, Is

です works like 'is' or 'to be' in English and is used to politely state something in everyday conversation. じゃない is the casual negative form meaning 'is not,' and it's often used in relaxed speech or in phrases like ～じゃないと思います ('I don't think it is...').

です is often used as the polite form of だ, which is similar in meaning to 'is' or 'to be' in English. It's polite but not overly formal, and it's often used in both speech and writing. In contrast, である is a formal (but not polite) expression mainly used in writing or formal speeches. One key difference is that である can appear in front of nouns in modifying clauses, like in 日本人である留学生 ('an exchange student who is Japanese').

です and でございます are both polite forms of 'is' or 'to be.' です is polite but commonly used in everyday conversation. でございます is extremely polite and formal, used in customer service, ceremonial speech, or other situations requiring a high level of respect.

The phrase ～がある is used to show existence or possession. For example, 本がある means 'There is a book' or 'I have a book.' On the other hand, です is used to identify something, like 本です ('It is a book'). がある is more casual and often used with close friends or in certain grammar patterns, while です is polite.

～んです・のです are used to clarify context, provide background information, give reasons, or express curiosity. In contrast, です without の or ん is a simple declarative form used to state facts or general statements. Using ～んです・のです adds emphasis, conveys intention, or creates a more explanatory tone by suggesting a larger context.

だ and です both function like the English 'is.' The main difference is politeness: だ is casual and used in plain speech, while です is polite. だ can't be used after い-adjectives, but です can, acting as a general politeness marker. You may still see だ in set expressions like ～だと思います, even in polite sentences.

です and だった・でした are all forms of 'is' or 'to be,' but they show different tenses. です is used for the present or future, like in あれは猫です ('That is a cat'). だった and でした are past tense—だった is casual, and でした is polite. For example, あれは猫だった means 'That was a cat.'