5 Calls for a Comma Before “Because”

Use of the word because as a subordinating conjunction — to link a main clause to a subordinating clause — should be simple, but a sentence’s meaning often hinges on whether it’s preceded by a comma.
A straightforward sentence such as “We’re off to see the wizard because of the wonderful things he does” requires no comma; the meaning of this sentence — “This is what we’re doing, and that is why we’re doing it” — is unambiguous. But when the sentence begins with a negative proposition, that’s not the case, as these examples show:
1. “Few adult Romanians speak English because it was forbidden during the Ceausescu era.”
This sentence, as (not) punctuated, absurdly implies a meaning of “This is not the primary reason adult Romanians speak English,” accompanied by the expectation of a follow-up sentence identifying one or more other causes for bilingual ability despite its prohibition.
But it doesn’t mean “There are more common reasons adult Romanians speak English”; it means “This is the reason few adult Romanians speak English.” Insert a comma, and the sentence tells you what, and then tells you why: “Few adult Romanians speak English, because it was forbidden during the Ceausescu era.”
2. “They don’t want to diagnose or treat Lyme disease because it is very costly to do so.”
Oh. Then why do they want to diagnose or treat Lyme disease? Again, a comma makes it clear that this sentence doesn’t serve to set up one or more alternate reasons; rather, the subordinating clause provides an explanation for the reluctance: “They don’t want to diagnose or treat Lyme disease, because it is very costly to do so.”
3. “Dementia can’t be ignored by the larger community because individuals with the disease cannot manage independently.”
Why, then, can dementia be ignored? That’s not what the sentence is trying to tell you. It’s explaining why the general populace should attend to the affliction: “Dementia can’t be ignored by the larger community, because individuals with the disease cannot manage independently.”
4. “I wouldn’t recommend chicken pox parties because of the risk.”
Tell me, then, why you would recommend them? (Aside: Said parties are often organized by groups of parents to deliberately expose their kids to chicken pox to get it over with.) The subordinate clause explains the statement in the main clause: “I wouldn’t recommend chicken pox parties, because of the risk.”
5. “The model couldn’t be applied to other sectors because it evolved to care for water, not civilization’s infrastructure.”
The implication is that the model could be applied to other sectors, but not for the reason stated. But the point is that it couldn’t be applied, and the reason follows: “The model couldn’t be applied to other sectors, because it evolved to care for water, not civilization’s infrastructure.”
See how a comma’s presence or absence can drastically change a sentence’s meaning? Sometimes, it’s important even when the sentence doesn’t begin with a negative proposition: “I know he got the biggest raise in the department because his wife told me” reads as if the writer is aware that the person got the raise because the person’s wife told the writer that the person got the raise — and the sentence turns into a Moebius strip. A comma nips this perpetual-motion machine in the bud: “I know he got the biggest raise in the department, because his wife told me.”

sumber