Is it simply a matter of preference? The em-dash can be used for any sort of interruption, and unless I'm unaware of some rule, I think this qualifies as one. Oftentimes I prefer the use of the em-dash in situations like this because I'm never quite sure whether a comma really gets the job done, or if it is technically proper. The em-dash offers a more abrupt break than the comma, which aligns better with how I want the sentence to sound, influenced by how I read. As for the technical aspect, I know there isn't really a good argument for why I feel that the use of a comma here may be improper—this isn't a comma splice. It's simply an interjection, an additional thought that is relevant to the meaning of the sentence, but not an essential piece of the sentence. I think of it as a flower in a woman's hair—the flower isn't essential, her hair is usually beautiful in and of itself, but the flower adds to the overall effect. At the risk of extending this metaphor too far, maybe this debate is as pointless as a debate about how to attach the flower—bobby pin or the stem alone?
. This is a standalone phrase which doesn't alter the whole sentence (could be omitted), therefore the em-dash is in order. The alternative is to consider if you'd have used brackets instead of the dash. If yes, then the dash is in order. IMVHO of course.
Why don't we expand the question to a general comma versus em-dash debate? I think there's plenty of room for interesting discussion, particularly considering the cases where they are interchangeable. When do you use an em-dash? When do you use a comma? Do you use both, or only one? Some examples:
a comma, em-dash and brackets are pretty much interchangable in fiction, but preference depends on style. --Passersby offered me nods and smiles—typical Charlestonian friendliness—and although I was in no mood for such pleasantries, it was my duty as a Charlestonian to return them. --Passersby offered me nods and smiles, typical Charlestonian friendliness, and although I was in no mood for such pleasantries, it was my duty as a Charlestonian to return them. --Passersby offered me nods and smiles (typical Charlestonian friendliness) and although I was in no mood for such pleasantries, it was my duty as a Charlestonian to return them. I'd probably not use a fragment with a comma in academic writing, for greater clarity: Passersby offered me nods and smiles, which was typical Charlestonian friendliness, and although I was in no mood for such pleasantries, it was my duty as a Charlestonian to return them.
I see no reason for debate here. We kind of agree on the basic use of Em dashes; whether you want to use them or not is a choice of style: which makes it a bit stupid to debate someone over style. And besides, turning everything into a debate is getting a bit irritating.
I couldn't disagree more. Perhaps using the word debate is misleading—I'm more interested in discussion than I am in a heated argument. I don't want to try and convince you that my style is correct, I simply want to find out why your preferences are the way they are. Discussion often leads to new ways of thinking—it's a great learning tool—and I don't see any problem with that here.
My take on this is that em dashes are over-used. They do have specific functions, such as setting off sources of quotes, but their parenthetical use should be sparing, at least in my opinion. A piece of text littered with dashes looks somewhat unpleasing on the eye, and often leads to a jarring reading experience, for me at least. However, when used sparingly they can add a more dramatic pause than a simple comma. It is a discussion on stylistic preference, sure. But I suggest it's a discussion worth having.
I tend to use em dashes when I want to emphasize the sub-clause, and commas when I want to include a sub-clause that is less important than the main clause. versus In the first case the important detail is that the house was on fire. In the second case I am clarifying that I went into the green house (versus one of another color). I also use em dashes when I have several commas in a sentence and I need to set a sub-clause apart: *I realize that this is a cumbersome sentence, but when working with grant applications I sometimes have obscure requirements to work with (like using only a single sentence) **Sadly, those numbers are accurate
