Learn Hardcore Japanese: mosi densya ga mata okuretara, basu de ikemasu. - If the train is late again, I can go by bus.

もし is a particle that marks a hypothetical “if” clause in Japanese. It makes the sentence conditional, roughly equivalent to “if” or “in case” in English. You’ll often see it paired with conditional endings like ～たら, ～ば, or ～なら.

Why is が attached to 電車 instead of は?

Here が marks 電車 as the subject of the subordinate (conditional) clause 電車が遅れたら (“if the train is delayed”). Using が highlights the new or important information—in this case, whether the train delays again—whereas は would topically frame “the train” as already-known information.

What nuance does また add in また遅れたら?

また means “again” or “once more.” Its presence tells us that the train has already been delayed at least once earlier, and you’re considering the possibility of another delay.

How is the conditional ～たら formed, and what nuance does it carry?

You take the past tense plain form of a verb (here 遅れる → 遅れた) and add ら to get 遅れたら. It expresses a condition that, when or if met, leads to the main clause. Compared to other conditionals, ～たら can imply “once X happens, then Y.”

Why is バスで used for “by bus”?

The particle で indicates the means or method of an action. バスで行く literally means “go by bus.” If you used に, you’d be marking a location or destination, not the transport method.

Why do we see 行けます instead of 行きます?

行きます is the standard “go,” whereas 行けます is the potential form, meaning “can go.” Here it tells you that taking the bus is a possible alternative if the train doesn’t run on time.

Could this sentence be made more casual?

Yes. Drop the polite ending ます and use the plain potential form:
もし電車がまた遅れたら、バスで行けるよ。

Why is there a comma after 遅れたら?

Japanese often uses a comma (、) to separate clauses for clarity, much like in English. Here it visually splits the “if” clause (電車がまた遅れたら) from the main clause (バスで行けます).