One of my favorite things about Japanese is that nouns are incredibly versatile.

Back when I was an English teacher, a Japanese student of mine once said:

You use so many verbs in English!”

The thing is, in Japanese—as opposed to in English—you can make a lot more sentences using only nouns and the copula だ.

For example, if you walk outside of your house, see that it’s raining, then say “Rain,” then your English sounds strange. However, this type of sentence construction is totally natural in Japanese, and you can just say:

雨だ。
あめ　だ。
It's raining.
Literally: “rain + [copula (=だ)]."

We take the noun 雨, "rain," then simply add だ to the end of it. (Note that this is a casual sentence. We'll see formal variants in time.)

Wait, wait, wait! Isn't is more common to drop the だ at the end of a casual sentence?
(*Cue Shakespeare voice) To だ, or not to だ... that is the question...
I'll level with you: I don't know how to explain this. Often だ gets dropped in casual language. Sometimes it does not get dropped. There are a number of factors at play, such as the gender of the speaker, the speaker's personal preferences, the length of the sentence, the words being used, and so on.
I have been asking a lot of Japanese speakers about this over the last couple of years, trying to formulate a good explanation as to when/how this happens, and how we can master it... but I haven't hit on any epiphanies yet. On the bright side, I have noticed myself developing somewhat of a better sense for this.
At the very least, I can say that including だ can add a "declarative punch" to a sentence, if you will.
Meh, we'll figure all of this out in time, yeah?

Virtually any noun that expresses a state or an event can be made into a full, natural sentence by combining it with だ.

Let's look at a few more examples of sentences like this that are much, much easier to construct in Japanese than they are in English.

Key Vocabulary

今日（きょう // today）

仕事（しごと // work; job）

雨（あめ // rain）

雪（ゆき // snow）

休み（やすみ // holiday; day off; break）

ライブ（ライブ // concert; live show）

デート（デート // date (e.g. with a boyfriend/girlfriend）

Sentences

今日は仕事だ。
きょう　は　しごと　だ。
I have work today.
Literally: “today + は + work + だ.”

今日は雨だ。
きょう　は　あめ　だ。
It’s raining today. / It’s going to rain today.
Literally: “today + は + rain + だ.”

今日は雪だ。
きょう　は　ゆき　だ。
It’s snowing today. / It’s going to snow today.
Literally: “today + は + snow + だ.”

今日は休みだ。
きょう　は　やすみ　だ。
Today’s my day off. / I don’t have work today.
Literally: “today + は + holiday / day off + だ.”

今日はライブだ。
きょう　は　ライブ　だ。
I’m going to that concert today. / Our concert is today. / The concert is today.
Literally: “today + は + concert / live show + だ.”

今日は彼女とデートだ。
きょう　は　かのじょ　と　デート　だ。
I have a date with my girlfriend today.
Literally: “today + は + girlfriend + と (=with) + date + だ.”

Note that I’m not saying that these are the only ways to form these sentences.

For example, it is also fine to express that it’s raining by saying:

雨が降っている。
あめ　が　ふっている。
It's raining.
Literally: "rain + が + is falling."

You’ll notice that in those sentences above, the English translations are all over the place. Every Japanese sentence is structurally identical, but the English ranges from “I have work today” to “I’m going to that concert today” to “It’s snowing today.”

The reason that the English is all over the place is that I’m translating these sentences out of context, which, though intimidating at first, is awesome for beginner-level students.

It's awesome because you can express complicated ideas without using complicated language... once you get used to manipulating context a bit.

Speaking of context, these sentences also serve as an awesome example of the subzero pronoun.

By "subzero pronoun" I mean the often-unspoken "subject" of Japanese sentences (if we can really use the word "subject" at all).

Looking at the simple sentences above, what do you think is the subject of each one?

A Japanese teacher might try to tell you that 今日 (きょう // today) is the subject, but if we look at the English translations, our subjects are ranging from “I” to “it” to “concert” to “today.”

That’s because the subject—assuming that we’re trying to force a “subject” in the English sense into this sentence—is coming after は in the form of the unspoken subzero pronoun.

(Note: For the sake of simplicity, in the following direct translations, I’m going to write “is” in place of だ, mostly because I think writing “is” will be easier to understand than writing “[copula],” or something like that.)

今日は（！）雨だ。
きょう　は　(！)　あめ　だ。
As for today, (!) rain is.
Literally: "today + は + (!) + rain + だ."

What is rain? The weather is rain. So we can infer that the subzero pronoun in this example is “the weather.”

Let's insert “weather” for the subzero pronoun:

“As for today, (weather) rain is.”

You may know that は (wa) is typically referred to as a "topic-marking particle." が (ga), on the other hand, tends to be referred to as a "subject-marking particle" or, in some cases, "identifier particle" or "pointer particle."

The example we're looking at here is a great example of why people like to call が a "subject-marking particle." The reason for this is that, if we try to write the subzero pronoun in Japanese, it makes sense to write "NOUN + が."

Like this:

今日は（！）雨だ。
きょう　は　(！)　あめ　だ。
As for today, (!) rain is.
Literally: "today + は + (!) + rain + だ."

↓　↓　↓

今日は（天気が）雨だ。
きょう　は　(てんき　が)　あめ　だ。
As for today, (the weather) rain is.
Literally: "today + は + (weather + が) + rain + だ."

As mentioned in an earlier lesson, は brings attention to whatever comes after it, and が puts a focus on whatever comes before it. If we want to force ourselves to identify (unspoken) subjects of Japanese sentences, we will consequently find them between は and が, as in that example above.

A couple more examples:

今日は（！）彼女とデートだ。
きょう　は　(！)　かのじょ　と　デート　だ。
As for today, (!) girlfriend with date is.
Literally: "today + は + (!) + girlfriend + と (=with) + date + だ."

今日は（予定が）彼女とデートだ。
きょう　は　(よてい　が)　かのじょ　と　デート　だ。
As for today, (the schedule / plan) girlfriend with date is.
Literally: "today + は + (schedule / plan + が) + girlfriend + と (=with) + date + だ."

I'm just guessing that 予定 might be the unspoken subject [subzero pronoun] of this sentence. We have no way of really knowing. More specifically, it should probably be something like 私の予定 (わたしのよてい), "my plan/schedule."

Newsflash: No one cares.

When people make sentences, they're not pontificating about what may or may not be the unspoken subject of each sentence, and which particle would be used before or after it. Instead, we just lean on our intrinsic human ability to communicate. We see a sentence like this:

今日は彼女とデートだ。
きょう　は　かのじょ　と　デート　だ。

...and by some dark magic, our brains are able to understand that it means:

I have a date with my girlfriend today.

It's fun to imagine what's happening behind the scenes... but it doesn't really affect our fluency that much.

This is my long, roundabout way of saying that you shouldn't really worry about what is or is not the subject of a Japanese sentence, just like you shouldn't fret about the differences between は and が. It's stuff you can learn in the background.

I really don’t want to freak anyone out, because this is probably going to sound really intimidating, but there are only very limited contexts in which this specific Japanese sentence will sound natural:

今日は彼女とデートだ。
きょう　は　かのじょ　と　デート　だ。
I have a date with my girlfriend today.
Literally: “today + は + girlfriend + と (=with) + date + だ.”

For example, if two male friends are getting coffee in the afternoon, and one of them asks:

A:
今日の予定は？
きょう　の　よてい　は？
What are you up to after this?
Literally: "today + の + plan/schedule + は？"

In this case, it would sound natural for the other guy to say:

B:
今日は彼女とデート。
きょう　は　かのじょ　と　デート。
I have a date with my girlfriend today.
Literally: "today + は + girlfriend + と (=with) + date."
Note: We're actually dropping the だ from the end of the sentence. We saw how this is common to do earlier in the course (remember?!).

But yeah, that’s only one situation in which it would be natural to use the sentence introduced above about having a date.

However, it would not work as an answer to this statement:

A:
なんかおしゃれだね。
なんか　おしゃれ　だ　ね。
You look kind of fancy today. // You’re kind of dressed up today, huh?
Literally: "sorta + stylish + だ + ね."
Note: なんか is a bit hard to define, but it's sometimes translated as "somehow" or "kind of."

In this case, it would sound natural for the other guy to say:

B:
今日は彼女とデートなんだ。
きょう　は　かのじょ　と　デート　なんだ。
I have a date with my girlfriend today.
Literally: "today + は + girlfriend + と (=with) + date + なんだ."
Note: This ～なんだ is the same as the ～んだ that we saw in the last lesson, only ～なんだ is what comes after nouns and na-adjectives.

Differentiating between デートだ and デートなんだ is not basic Japanese. But then, neither is breaking down the fundamental structure of a sentence.

Please keep in mind that what we're looking at in our lessons so far is not enough information to sound natural when speaking Japanese, as that is the ultimate challenge for learners (and for me, too). And we have to be patient in approaching that level. Learning to sound natural is one of the awesome bonuses of reaching an advanced level at any language.

Until then, we only need to worry about getting our point across. Whenever possible, I will try to include notes on small nuances and native-sounding speech, but it’s nothing to really fret over. You will get a feel for it over time, I promise.

Whenever I write hard-to-understand notes on the subtleties of Japanese, please don’t think, “This is too hard.” Instead, think, “I can’t wait to understand what he’s talking about.” Think, “I’m building native feels.” Think, “This is awesome.”

I learned the vast majority of this stuff about natural expressions and word nuances though high levels of exposure to Japanese. No one ever explained these things to me. So if I can learn it that way, then you can probably learn it ten times faster by getting high levels of exposure and reading my painfully formulated explanations.