Sorry to resurrect an old post, but I don't think Write Write received a full answer, and I'm a bit curious about this topic myself. Ruslana is right that commas should not set off most adverbial dependent clauses that occur at the end of a sentence. However, sometimes a comma is necessary before because for the sake of clarity. Here's an example from Fowler's Modern English Usage:
I know he committed suicide, because his wife told me.
In this example, the comma lets readers know that I heard about the suicide from the wife. Without the comma, one might believe that the reason that the man decided to committ suicide was because his wife told me something. You may also find a comma before because if the adverbial clause that follows is parenthetical. Here's another example from Fowler's:
He’d have to watch his step…not to make a hash of things, because of over-anxiety.
I might write it without the comma, but I suppose the comma helps illustrate that the over-anxiety is more of an afterthought and not the driving force. However, I'm a bit confused myself--
Question: does because of perform a different role than just plain because? That is, I've seen it referred to as a preposition instead of subordinating conjunction. Could this be part of the reason there's a comma before the because? And what about when because begins a sentence? I've read that most introductory adverbial dependent clauses (i.e., clauses that answer the why question--because clauses) should not have a comma after the initial phrase, but Fowler's provides this sentence as a legitimate example of because: Because of the deterioration of the sugar in the blood it was decided, after consultation, to carry out an exchange blood transfusion.
Why?
-Andrew