I know US punctuation puts a capital letter after a colon, whereas UK English does not. What's the situation with a dash? I don't know how I've got by so long without this issue coming up, but now I find I have a sentence similar to this (this isn't the actual one, so I'm only interested in the punctuation, not re-writes): A thought struck him -- no one would find out about the robbery now, with Jackson dead. Is it better/possible/impossible to have the part after the dash starting with a capital letter? A thought struck him -- No one would find out about the robbery now, with Jackson dead. I've researched a bit, but can't get much of an answer to this.