Learn Hardcore Japanese: huyu ha atatakai suupu ga tanosimi da.

は marks the topic: 冬は means “as for winter,” which in practice reads like “in winter.” It sets the seasonal context for the comment that follows. It doesn’t mean “in” by itself; it just frames what you’re talking about.

Why is が used before 楽しみだ instead of を or は?

With 楽しみだ, the thing you look forward to is marked by が. The pattern is: X が楽しみだ = “I’m looking forward to X.”

を doesn’t work with 楽しみだ (it’s not a verb).
は would add contrast/topic nuance (e.g., “As for warm soup, at least that is something to look forward to”), which isn’t needed here.

Who is the subject here? Where is “I”?

Japanese often leaves the subject implicit. Here it’s understood from context—usually the speaker (or people in general). If you need to be explicit, you can say 私は冬は… or みんなは冬は…, but it’s usually unnecessary.

What’s the difference between 楽しい and 楽しみ?

楽しい is an i-adjective meaning “fun/enjoyable” (e.g., イベントは楽しい = “The event is fun”).
楽しみ is a noun meaning “(something to) look forward to; a pleasure” (e.g., イベントが楽しみだ = “I’m looking forward to the event”).
You don’t say スープは楽しい to mean “I look forward to soup.”

How does 楽しみだ differ from 楽しみにしている?

Both can mean you’re looking forward to something:

X が楽しみだ: a simple state/judgment (“X is something I look forward to”).
X を楽しみにしている: emphasizes the ongoing feeling of anticipation; slightly more active or process-like.
Politeness: 楽しみです / 楽しみにしています.

Is 暖かい the best kanji choice for soup? What about 温かい or 熱い?

温かい: “warm” for objects you touch/eat/drink (common for soup).
暖かい: “warm” for ambient temperature or a warm atmosphere/feeling. It can be used for food, but many prefer 温かいスープ.
熱い: “hot” (physically hot). 熱いスープ = “hot soup.”

Can I say 冬には instead of 冬は? What changes?

Yes. 冬には adds a bit of focus/contrast on “in winter (as opposed to other times),” making the seasonal framing slightly stronger. Both are natural.

Why is there だ at the end? Can I use です?

だ is the plain/copula form used with nouns and na-adjectives. Here it attaches to the noun 楽しみ.
Polite version: 冬は暖かいスープが楽しみです.

Is the spacing between words normal in Japanese?

No. Standard Japanese doesn’t use spaces between words. The sentence is normally written as 冬は暖かいスープが楽しみだ。 Spaces are often added in learning materials to show word boundaries.

How do you pronounce the sentence?

Fuyu wa atatakai sūpu ga tanoshimi da.
Readings: 冬(ふゆ), 暖(温)かい(あたたかい), スープ, 楽しみ(たのしみ), だ.

Can I switch the word order, like 暖かいスープは冬が楽しみだ?

No; that would make “winter” the thing being looked forward to by “warm soup,” which is nonsensical. The natural pattern is topic (冬は) + clause (暖かいスープが楽しみだ). Keep 暖かい directly before スープ, and 楽しみだ at the end.

How do I make it negative or past?

Negative (plain): 冬は暖かいスープが楽しみじゃない。
Past (plain): 冬は暖かいスープが楽しみだった。
Past negative (plain): 冬は暖かいスープが楽しみじゃなかった。
Polite: 楽しみではありません／楽しみでした／楽しみではありませんでした.

Why can’t I say 冬は暖かいスープを楽しみだ?

Because 楽しみ is a noun taking だ, not a verb that takes を. Use either:

冬は暖かいスープが楽しみだ (noun + が
- 楽しみだ), or
冬は暖かいスープを楽しみにしている (verb phrase with を).

What grammar role does 暖かい play here?

暖かい is an i-adjective in attributive form modifying the noun スープ (“warm soup”). The だ at the end attaches to 楽しみ (a noun), not to 暖かい (you can’t say 暖かいだ).

Is 楽しみ a noun or an adjective? I’ve seen 楽しみな.

It’s primarily a noun, but it can function like a na-adjective before nouns: 楽しみなイベント (“an event I’m looking forward to”). As a predicate you use the copula: 〜が楽しみだ／です.

How can I say this more strongly, like “I can’t wait for warm soup in winter”?

Use intensifiers:

冬は暖かいスープが楽しみでたまらない。
冬は暖かいスープが本当に楽しみだ。
冬は暖かいスープが楽しみでしょうがない。

What if I mean “I enjoy warm soup in winter” (while drinking it), not “I look forward to it”?

Use 楽しむ or 好き:

冬は暖かいスープを楽しむ。
More natural everyday phrasing: 冬は暖かいスープが好きだ／をよく飲む／を味わうのが好きだ。