Learn Hardcore Japanese: asita ame ga huranakattara, tomodati to issyo ni kouen de sanposimasu. - If it doesn’t rain tomorrow, I will take a walk in the park with a friend.

Because the pattern 〜たら attaches to the plain past form, even when talking about the future. It doesn’t mean “past” here; it just forms the conditional “if/when.” Conjugation path:

降る (to fall) → 降らない (not fall) → 降らなかった (did not fall) + ら → 降らなかったら (“if it doesn’t rain” for tomorrow).

How do 〜たら, 〜ば, and 〜なら differ in this sentence?

明日雨が降らなかったら … (most neutral/natural for specific, time-bound conditions)
明日雨が降らなければ … (a bit more formal or general/hypothetical)
明日雨が降らないなら … (“if it’s the case that it won’t rain,” often based on an assumption or information like a forecast) All are correct, but 〜たら is the default choice here.

Can I add もし? Where does it go?

Yes. Put it at the start of the conditional clause: もし明日雨が降らなかったら、… / もし明日雨が降らなければ、… / もし明日雨が降らないなら、…. It adds “if by any chance/if indeed,” and is optional.

Why 雨が and not 雨は?

が marks “rain” as the grammatical subject of 降る. Using は would topicalize and often contrast, which sounds odd in a negative conditional like this. Stick with 雨が降らなかったら. You can topicalize “tomorrow” instead: 明日は、雨が降らなかったら…

Where is the subject “I/we”? Why isn’t it stated?

Japanese often drops subjects when they’re clear from context. Here, it’s understood as “I/we.” Also, 友達 doesn’t specify number by itself—it can be “a friend” or “friends” depending on context.

Why use both と and 一緒に in 友達と一緒に? Can I use only one?

友達と一緒に散歩します is the most explicit and common (“together with a friend/friends”).
友達と散歩します is also natural.
一緒に散歩します means “take a walk together” but doesn’t say with whom. Avoid dropping と before 一緒に (e.g., 友達一緒に)—that’s ungrammatical.

What is the に in 一緒に doing?

It’s part of the fixed adverb 一緒に (“together”) and not a separate particle marking time/place. Think of 一緒に as one word.

Why 公園で and not 公園に? Can I use 公園を?

公園で散歩します: で marks the location where the action happens (correct here).
公園に散歩します: not natural; に doesn’t mark the location for 散歩する.
公園を散歩します: also correct; を marks the route/area you stroll through (emphasis on moving through the park). You can also say 公園に散歩に行きます (“go to the park to take a walk”).

Can I say 雨じゃなかったら instead of 雨が降らなかったら?

Yes, in casual speech 雨じゃなかったら行く is common and understood as “if it’s not rainy.” It’s a broader/weather-state wording. Textbooks prefer the verb pattern 雨が降らなかったら because it directly ties to the event of rain.

Is it okay that the conditional clause is plain form but the main clause is polite (散歩します)?

Yes. Subordinate clauses (like conditionals) are normally in plain form even in polite speech. You can also make everything plain (散歩する) or use other polite conditionals like 降らなければ. Avoid overly stiff forms like 降りませんでしたら in everyday conversation.

Could I use 降りませんでしたら for extra politeness?

It’s grammatically possible but sounds stiff and uncommon in daily speech. Prefer 降らなければ or stick with 降らなかったら + polite main clause.

Why does 散歩します (non-past) refer to a future action?

Japanese non-past (〜ます/〜る) covers both present and future. The time word 明日 sets it in the future. If you want to stress intention, you can also say 散歩するつもりです.

Can I change the word order?

There’s flexibility, but the natural flow is: time → condition → companions → place → action: 明日、雨が降らなかったら、友達と一緒に公園で散歩します。 Keep 明日 near the clause it modifies and avoid odd placements like 雨が明日降らなかったら, which sounds unnatural.

Do I need the comma after 降らなかったら?

It’s not strictly required, but it’s standard and improves readability by marking the boundary between the conditional clause and the main clause.

Are spaces between the words normal in Japanese?

No. The spaces in the provided sentence are for learners. Standard Japanese writing doesn’t insert spaces between words, but it does use punctuation like the comma 、.

Can I drop some particles in casual speech?

Yes, in very casual speech you might hear 明日雨降らなかったら… (dropping が). Learners should keep particles until they’re comfortable with when omission sounds natural.