Does だ in 予定だ add emphasis?


I thought `<noun>+だ` at the end of a casual sentence adds emphasis (unlike the
constructions where だ is needed for grammatical reasons such んだ, だから, だけど). So
when I want to simply share some information in a mild tone, without any
emphasis, I end with just `<noun>`.

However, when I looked up 予定 in 研究社 (in the sense "I'm planning to..."), I saw
all the informal sentence examples end with `<noun>+だ`:

  * 土産は帰りに買う予定だ.
  * 彼女は, 来月から香港に移り住む予定だ.
  * 今日は顔だけ出してすぐ帰る予定だ.

Would it sound natural to say "土産は帰りに買う予定" etc. when no emphasis is intended?
Or did I misunderstand the role of だ?




土産は帰りに買う予定だ is something one might write in their personal diary, but it's not
something an ordinary person actually says out loud in reality. In ordinary
informal conversations, we almost never end a sentence with だ; it's usually
too blunt and unfriendly. Instead, we use 買うと思う, 買うつもり, 買う予定, 買おうかな, 買うよ, 買うね,
and so on.

However, since conciseness and "compliance to standards" are important for any
dictionary, we normally see だ as part of example sentences whenever it's
grammatically valid, even though people don't usually say 予定だ in informal
sentences. Even です is not suitable as an example in a dictionary because it's
one character longer. You have to get used to this fact when using a Japanese
dictionary. There are simply too many variations in the way real Japanese
sentences can end, and dictionaries have no option but to stick to だ as the
shortest and most canonical one.




As others have mentioned, whether to use だ or not is not fundamentally about
adding emphasis, that is actually really more a side-effect of various other
factors.

In reality, ending with だ is technically simply the complete form of a full
casual sentence, and so arguably should be seen as the "standard"
construction. It is what most people are taught in textbooks, etc. However, it
is the case that in the real world, many speakers, when speaking casually,
will just tend to drop the だ in many situations. Because of that, _when people
would normally leave off the だ_ but instead choose not to, it can sound more
forceful or emphatic as a result.

However, it's also not the case that everyone always leaves off だ when
speaking casually either. Whether someone will choose to leave it off or not
depends on the situation, and the sentence. In particular, だ is typically
omitted most of the time when saying short sentences of only a few words, but
it is more common to actually leave it on when speaking longer sentences (I
think partly because it can serve as a useful "end of sentence" marker to help
the listener sort out more complex sentence grammars).

So in the examples you quoted, because they are longer sentences, ending with
だ does not necessarily sound "emphatic", because it's actually more normal to
keep it on the end of the sentence in that sort of situation anyway.

