Is it really necessary to put a comma before since clause?
If I omit the comma before since clause in formal writing, will that be taken as a mistake?
We often use as and since when we want to focus more on the result than the reason. As and since are more formal than because. We usually put a comma before since after the main clause:
- [result]I hope they've decided to come as [reason]I wanted to hear about their India trip.
- [result]They're rather expensive, since [reason]they're quite hard to find.
We use since as a subordinating conjunction to introduce a subordinate clause. We use it to give a reason for something:
Sean had no reason to take a taxi since his flat was near enough to walk to.
- Since her husband hated holidays so much, she decided to go on her own.
- They couldn't deliver the parcel since no one was there to answer the door.
Best Answer
No; or rather, only in exactly the same way as it’s ‘necessary’ to put a comma before an ‘as clause’ like the one in your example.
Formal writing or not, in modern English, at least, most commas are optional.
My limited experience of it is that Cambridge is one of the worst English dictionaries available, which is why almost no-one living in England has heard of it.
Prove this for yourself by comparing anything of which you are not certain to Oxford or Webster, for instance. Not in my but in your view, which is better?
With or without any comma, ‘I hope they’ve decided to come as I wanted to hear about their India trip’ throws up at least three questions which might not be truly important in or of themselves, but as evidence for the reliability of a dictionary, cut about as much mustard as a dead, red herring. At best, that sentence is unnatural; it’s rather clearly not a quoted but an artificially constructed example, and not a good one.
In the same way ‘Sean had no reason to take a taxi since his flat was near enough to walk to’ is wholly comprehensible, but was it supposed to be merely comprehensible, or intended to give a clear and helpful illustration of a specific point, while at the same raising no irrelevant questions?