gamecomplete wrote:I'm still curious about one thing. Why wouldn't we need a connector before "but". I've always been taught that connectors such as and, but so, etc. require a comma before hand. To your point, I also noticed that the official guide has a comma sometimes, and other times not. It just seems really random. I'd appreciate your insight!
The choice of whether to use a comma before a conjunction such as
but,
and, or
because depends on the context.
Look at the following sentence. Generally, unless you were seeking to emphasize the fact that you also saw Fred, you would not put a comma before
and.
I saw Jill and Fred.
So in a simple two element list, generally there is no need for a comma.
Look at these.
I saw not only Jill but also Fred.
I ran up the stairs and dove through the doorway. (another list)
It is either a dog or a wolf.
None of them require commas.
So what does require a comma?
One thing that requires at least one comma is a list with three or more elements.
I ran up the stairs, dove through the doorway and shut the window.
In that construction, you could put a comma, often called the "Oxford comma" before
and or leave it out, people do it either way, but you need one between
stairs and
dove.
In the GMAT questions you are talking about, I think what you are seeing are situations in which the comma separates two clauses.
Jim ran up the stairs, but he could not find the door.
Notice that before and after the comma there are two clauses, each with a subject and verb.
Jim ran....
he could not find
The convention is to separate clauses with a comma.
Fred asked many questions, because he wanted to find out what really happened.
While Jeremy was studying, his brother ate all the pudding.
Natalie made cookies, and she delivered them herself.
If we shortened that last sentence and made the second clause part of a list, then we could leave out the comma.
Natalie made cookies and delivered them herself.
