I often see writers and editors putting a comma before the word because, for example, This won’t surprise anyone who has known her for a long time, because she has always espoused both liberal and conservative perspectives.

The problem with this construction is that the word because is a subordinating conjunction, which means that it introduces a subordinate clause. When there is an independent clause first, and then a subordinating conjunction is used to introduce another clause, that subordinating conjunction does not get a comma before it.

• This won’t surprise anyone who has known her for a long time because she has always espoused both liberal and conservative perspectives.

If, however, a clause that starts with a subordinating conjunction comes at the beginning of a sentence, then a comma must be used after the clause.

• Because she has always espoused both liberal and conservative perspectives, this won’t surprise anyone who has known her for a long time.

Other examples:

• I stayed home instead of venturing out for the evening because I was tired.

• Because I was tired, I stayed home instead of venturing out for the evening.

• His explanation did not satisfy her but, rather, made her suspicious because she’d just seen a similar plot on the late, late show.

• Because she’d just seen a similar plot on the late, late show, his explanation did not satisfy her but, rather, made her suspicious.

Sherry’s Grammar List