Not to Mention Comma

This all seems to be weighing down on him, not to mention [that] he is haunted by his past.

It’s best not to substitute that with a comma.

Oh, I see. But I hear "not to mention" without a "that" after it all the time, though. Is that sentence not stand-alone? Is that why you connected it to the first part as if it's a dependent clause?

SnarfBut I hear "not to mention" without a "that" after it all the time, though.

Idiomatically, that is usually implicit in the expression. Note how I bracketed the word in my previous post.

SnarfIs that sentence not stand-alone? Is that why you connected it to the first part as if it's a dependent clause?

Yes, that’s

Aspara GusIdiomatically, that is usually implicit in the expression. Note how I bracketed the word in my previous post.

Oh, so it's either "that" or a comma has to be there, however "that" is better.

No, no, no. You should never use a comma there, regardless of whether that is included. Even when you don’t use that, it’s still there, which is why I advised not to use a comma as a substitute.