Learn Hardcore Japanese: kamera ga kowareta node, mise ni henpinsimasu. - Because the camera broke, I will return it to the store.

が marks the subject and often introduces new or factual information—in this case, that the camera is what broke. Using は would topicalize it: カメラは壊れたので… means “As for the camera, since it broke…,” which can sound more contrastive or as if the camera was already the topic. Both are grammatically fine; が feels neutral/new-information, は feels topical/contrastive.

Why is 壊れた in the past but 返品します is in non-past? Is that a tense mismatch?

This is normal in Japanese. The clause with 壊れた states a completed event (“it broke”), while 返品します states a present decision/near-future plan (“I will return it”). Japanese non-past covers both habitual and future actions.

What’s the difference between ので and から for “because”?

ので: softer, more explanatory/objective, often preferred in polite contexts.
から: more direct/casual, can sound a bit stronger or personal.
Here, both 壊れたので and 壊れたから work. With します, ので feels especially natural and polite.

Could I say 壊れているので instead of 壊れたので?

Yes.

壊れたので emphasizes the breaking event happened.
壊れているので emphasizes the current state (it is broken).
For returns, both are common; 壊れているので slightly highlights the defective state.

Is 壊れる transitive or intransitive? What if I want to say “I broke the camera”?

壊れる is intransitive (“to break” by itself): カメラが壊れた.
The transitive partner is 壊す (“to break [something]”): 私がカメラを壊したので、店に返品できません (“Since I broke it, I can’t return it”).

Where is the direct object of 返品します? Shouldn’t there be を?

It’s omitted because it’s clear from context. You can say it explicitly:

カメラを店に返品します。
Word order is flexible: 店にカメラを返品します also works. The most typical is object first, then destination: カメラを店に返品します.

Why 店に and not 店へ or 店で?

に marks the recipient/target: returning the item “to” the store is 店に返品する (most standard).
へ also marks direction, but it’s less specific about the target; it’s possible but less common here.
で marks the place where the action occurs: 店で返品します = “I’ll do the return at the store.” It focuses on the location rather than the recipient.

What’s the nuance difference among 返品する, 返す, and 返却する?

返品する: return purchased goods to the seller (store/online).
返す: return something to its owner in general (e.g., borrowed items, someone’s pen).
返却する: formal/polite “to return” (often for libraries, rentals).
For a defective purchase, 返品する is the precise verb.

Is 返品します future, intention, or a plan? How could I make the intention clearer?

Non-past 返品します can mean “will return” or “intend to return.” To be explicit:

返品するつもりです。 (I intend to return it.)
返品する予定です。 (I plan/schedule to return it.)

Can I use polite form before ので, like 壊れましたので?

Yes. 壊れましたので is common in formal speech and customer-service contexts. In everyday speech, the plain form before ので (壊れたので) is also perfectly natural. Both are correct; choose based on politeness level.

How would I say this politely to a store clerk?

すみません、カメラが壊れたので、返品したいのですが。
Even more formal: すみません、カメラが壊れましたので、返品をお願いできますか。
If you want to sound extra polite: 返品させていただけますか。

Should I say 店, お店, or 店舗?

店（みせ）: neutral, everyday.
お店: adds politeness/respect toward the store; common in conversation.
店舗（てんぽ）: formal/businesslike, common in written notices.
Any is fine; choose based on context.

Is the comma after ので required?

No. The Japanese comma 、 is optional and used for readability. …壊れたので店に返品します。 is also correct.

If I want to specify “the store I bought it from,” how do I say that?

Use a relative clause:

買った店に返品します。 (I’ll return it to the store where I bought it.)
More explicit: このカメラを買った店に返品します。

How does ので work with nouns and na-adjectives?

With nouns/na-adjectives, use なので:

Noun: 故障（こしょう）なので、返品します。 (Because it’s a defect…)
Na-adjective: 不良品（ふりょうひん）なので、返品します。 (Because it’s defective…)

How about using ため（に） instead of ので?

For cause, ため (often without に) is more formal/written:

壊れたため、店に返品します。
It sounds firmer and a bit more formal than ので. Note ために also means “for the sake of/in order to,” so for “because,” writers often use ため (no に).

How do you read the key words?

カメラ: kamera
壊れる: kowareru (past: 壊れた: kowareta)
店: mise
返品する: henpin-suru (polite: 返品します: henpin-shimasu)