のだ (んだ, のです, んです, or の) seems to create an information deficit. There was an article written by Derek Schaab about this.
The の here is called a formal noun. It is very often translated to "It is that~", "the case", "the situation" or "the fact". When used to end a sentence, it may imply that it is an explanation to some previous context (filling up the ...
～んです is a contraction of ～のです, which in turn is the polite form of the plain/informal ～のだ (which is also seen sometimes as ～んだ.)
～のです/～のだ are used to emphasize the previous statement. According to Daijisen and Daijirin, のです emphasizes explanations of cause/reason/basis etc. In the forms of ～んですか/～のですか, it can create an emphasized or even demanding question.
One usage that I was taught and is not mentioned above for んです is to soften a question or statement.
レストランに 行きたいです I want to go to a restaurant.
is a bit demanding or matter-of-fact. Changing to 行きたいんです softens this. Imagine a friend asks you about what you both should do for lunch. 行きたい sounds a bit forceful, like you will consider nothing ...
There is a slight difference between 〜かもしれない and 〜なのかもしれない that is really hard to explain, but is nonetheless good to know because in a lot of cases one will be much more natural than the other.
One way to look at it might be:
X は Y かもしれない → X could be Y
X は Y なのかもしれない → It could be that X is Y
For example, if you heard someone coming down the chimney on ...
Yes たまに means "occasionally."
んだ at the end of the sentence is not related to たまに. This んだ is the colloquialism for のだ, which is often called explanatory no(da). In your sentence, んだ is not necessary but used for mild emphasis. Most of the time you don't have to translate this のだ explicitly.
Explanatory のだ （んだ）
What is the meaning of ～んです?
How is the "...
So-called "explanatory の" has many functions and it's not a good idea to look for a direct equivalent in English. See this answer and this one, and you can see that の is used way more casually than "because". Using "because" to translate の is sometimes okay, but unacceptable in many cases.
ので and から are both "because", which is something you use to ...
As you can see in this chart, な in なのよ is the attributive form of だ ("the copula"). And だ/です safely works as the predicate of a sentence. (e.g., 今日は日曜日です, 私は学生です)
よ is a feminine sentence-end particle.
Here both は and が are used in one sentence, and this can be understood in the same way as you interpret 私は猫が好きだ or 彼は背が高い.
勝負 here is a noun which means the ...
Firstly, 食堂の食べ物はあまり好きじゃないだ。 is not grammatical. じゃない cannot be followed by だ in standard Japanese, so the correct version of this sentence with the ん removed would simply be 食堂の食べ物はあまり好きじゃない。
As for the meaning, this is a straightforward ordinary usage of the "explanatory の", so it simply adds a certain explanatory nuance to the statement. A similar effect ...
んです itself doesn't get conjugated, right?
んです（≂ のです; particle の + copula です） conjugates to:
んです、んでした、んでしょう、(んでして、) -- polite
んだ、んだった、んだろう、んで、んなら -- plain
And, as with な adjectives, な also gets added after nouns. But how would this work in the past tense?
You replace な with だった, as in:
Yes, this is a typical example of explanatory-の. Looking at the source, we can see this sentence is trying to explain why the アザラシ was found in the mountain.
The animal ended up entering the river.
It is that the animal ended up entering the river.
The animal may have ended up entering the river.
I think you did not refer to the right chapter of your textbook. If you have already read the proper explanation about this の, you should know it's mainly for explanation or clarification. Think of this の as a milder version of "that is to say", "because", "I mean", etc. Your first sentence, "クリスマスの前デパートはいつも込んでいるんです。", is not a natural sentence without a ...
のです is a constructuon that:
asks for or gives an explaination or information (or additional infos)
when you want to be sure that what you imagined or judged from a context is true or not
(Someone entering the office with an umbrella) 雨が降っているんですか。
when you express your interpretation or you understand something that wasn’t clear ...
Questions of のだ forms mean that you are trying to confirm if your judgement from your observation is true or not, opposed to simple questions.
For example, simple くれる？ means that your are asking someone to give something while くれるの？ means that the opponent seems giving it and you are confirming if he's really doing.
Negative questions are basically ...
Yes, ので is related to のだ. This の sort of means 'thing' or '(the) thing is' in the sense of 'it is the case is that...'.
For this reason, the difference between さむい？ and さみいの？is that the first is a simple question, whereas the latter implies that you have reason to think that the other person is cold. Perhaps they are wearing a heavy jacket or they asked to ...
ので has similar meaning to から in that they can both mean "because, given that..."
のだ, or のです are versions of んだ/んです that are more often used in writing and they don't really mean "because", they just imply the speaker or writer is explaining or emphasizing things. It's quite hard to explain, you can read up on it here:
It looks like rain. I'll take my umbrella. (I'll take my umbrella, because it looks like rain.)
These two have the same meaning and interchangeable as colloquial expression.
「から」と「ので」にあるわずかな違い There is slight difference between the two.
ex-3: 君が『もういらない』って言ったから、あの本は捨てたよ。You said ...
I also would like to add my information gained from my teacher at college. He says while the above explanation describes in great details in what context we use 「んだ」 or 「のだ」, basically it cannot be translated as the expression of cause, basis, conclusion, restatement, or confession. According to his academic research on Japanese language 「んだ」 or 「のだ」only ...