21

だ is the plain-form copula (the "is; to be" word). In the plain form, い adjectives already form a complete predicate (the piece of a sentence or clause that can complete that sentence or clause). In translation, it's like the い adjective already includes the "is" meaning -- so 速い would be "[it] is fast", not just "fast". Since だ is only used to provide a ...


14

Grammatically speaking, there really are no adjectives in Japanese. i-adjectives are just special verbs. i-adjectives have many of the same inflections as do verbs, and they fulfill a grammatical role essentially equivalent to that of verbs. Therefore, 電車は速い is a complete sentence meaning "the train is fast", where 速い is the predicate. i-adjective + です ...


10

いえ is definitely used informally for いいえ, though it's not super casual. More casual options include いや, ううん, or 違う. That being said, you don't necessarily need a word that means 'no'; you can reply to 「フランスに行ったことある?」with just 「ないよ」


9

The first sentence 「ジュースなりコーラなり、お[好]{す}きなものをどうぞ。」 is perfectly natural. It is asking you to choose whatever you want to drink and "juice" and "cola" are only two examples of what is available. Point is you have other choices as well. The second sentence is different. By using 「か」, the speaker is giving the addressee two choices only --- "juice" and "...


5

お母さん (okaasan) is the polite form of "mother". You use it to address your own mother or when talking about the mothers of other people. 母親 or just 母 (haha) is the plain form of "mother". You use it to be humble when talking about your own mother to other people, or when politeness is not necessary.


5

I think the relationship between お母さん and 母親 is like that of mom and mother, in English.


5

応援する is an expression that can have a lot of different meanings. The most basic meaning is simply stating that you hope something goes well. This also means that you can use 応援する even when talking to people you have just met. 将来{しょうらい}の夢{ゆめ}は何ですか? Do you have any dreams for the future? カフェやりたいです。I want to run my own coffee shop. いいですね!私も応援{おうえん}...


3

Of course a sentence like 鳥は飛ぶ ("Birds fly.") is 100% grammatically correct. It's 100% standard, too; no slang/dialect is concerned. I'm not an expert, but you never need a professor nor a linguist to judge the correctness of such a simple sentence. Don't be that skeptical about your textbook. But did your textbook really call this casual style? I ...


2

The main difference is that you can't use はは to talk about someone else's mother. I think you must use お母さん in that case. Usually Japanese people call their mothers おかあさん when they talk to them directly. はは is used to talk about your mother to other people.


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