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I have noticed that some native english speakers use the "-" sign to explain some additional things in a sentence: eg

Sophie is going to the shop - which happened to be around the corner - to buy some groceries.

Before knowing this notation I would write the same sentence as follows:

Sophie is going to the shop, which happened to be around the corner, to buy some groceries.

To me the "-"-sign seems much clearer than a comma. Am I using the "-" correctly. If so what is the difference between a "," and a "-".

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    Note that there is a difference between a dash ( — ) and a hyphen ( - ).
    – Andrew Leach ♦
    Oct 14, 2013 at 15:17
  • Both commas and dashes serve specific roles as punctuation. The only case they truly overlap is the way you've used them here. You wouldn't, for instance, use dashes in place of commas for lists: "I would like to buy apples -- bananas -- pears."
    – MrHen
    Oct 14, 2013 at 15:55
  • Personally I often use the dash a lot in colloquial written messages such as in chat rooms or comments. I use more commas when I'm trying to be more formal/less colloquial so I would use the comma more than the dash in a question or answer here for instance. But I'm sure I actually use both and unless I'm being very formal I'll use a single hyphen character to stand in for a dash.
    – hippietrail
    Oct 14, 2013 at 16:44
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    @AndrewLeach: Not only that, there are also differences between the many kinds of dash: en dash (–) and em dash (—) are probably most common in English, and quotation dash (―) is also very common in many languages.
    – hippietrail
    Oct 14, 2013 at 16:57
  • Previous discussion at Parentheses vs. double commas vs. dashes to provide additional detail and the related questions linked from there. And as others have pointed out, using hyphens, as you just did, is incorrect.
    – RegDwigнt
    Oct 14, 2013 at 23:06

4 Answers 4

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Dashes, commas, and parenthesis are similar in that they are all used for parenthetical elements in a sentence, but they are are not identical.

The 'normal' is to use commas: the cat, which was dead, was in the middle of the road

Dashes are used when you want to 'shout' the parenthetical element, or it is surprising in some way: the cat - which was dead - was in the middle of the road

Dashes should also be used when the parenthetical element itself contains a comma: the cat - which was dead, and rather flat - was in the middle of the road

Parenthesis, which are slightly different in needing an opening and closing bracket, are used when you want to 'whisper' the parenthetical element: the cat (which was dead...) was in the middle of the road

There is no right or wrong as such; it is more of a style thing.

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  • With your particular example, all three versions are grammatical. But there are different types of parentheticals (see the Nichol article). With some parentheticals, the comma punctuation just doesn't work.
    – Edwin Ashworth
    Oct 15, 2013 at 21:59
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I'll import what I posted on a now-closed thread:

Perhaps it would be better to address parentheses [as in OP's example] as parts of sentences before discussing the punctuation involved; it can be confusing that the word has such a dual role. Jose Carillo comments:

... information ... set off by the punctuation marks — whether by commas, dashes, or parentheses — is called a parenthetical [or simply parenthesis, EA], and its distinguishing characteristic is that the sentence remains grammatically and semantically correct even without it. A parenthetical is basically added information; however, it isn’t necessarily optional or semantically expendable. It may be needed to put the statement in a desired context, to establish the logic of the sentence, or to convey a particular tone or mood for the statement. In fact, the punctuation chosen for a parenthetical largely determines its optionality or importance to the statement.

Carillo goes on to discuss the choice between commas, dashes, or parentheses to set off parentheses (parentheticals). He may be over-analytical; it is true, however, that commas signal the least abrupt interruption to the matrix sentence and dashes the most abrupt.

Mark Nichol discusses different uses of parentheticals, though parentheses would not be preferred over commas say for all types in all situations.

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  • This is all very nice, but how does it answer the OP's question?
    – Roaring Fish
    Oct 15, 2013 at 4:08
  • As MrHen implies, commas and dashes have varied roles in English. The above answer confirms the nature of and endorses the role they play in OP's example (setting off a parenthetical). It also addresses the nature of parentheticals — that their omission, while leaving a grammaticality and semantically acceptable matrix sentence, may drastically reduce the semantic content of the whole. It also attempts to tie in the importance of the omissible material to the optimal choice of punctuation, along with the abruptness of the interruption the parenthetical makes when included.
    – Edwin Ashworth
    Oct 15, 2013 at 8:34
  • The OP asks 'what is the difference between a "," and a "-". He wants to know how to use them, which you don't address. If you want to tell him at length what a parenthetical clause is, that is fine even though he didn't ask for it. It does no harm and may help him, but unless you also tell him how to choose between dashes and commas you haven't answered his question.
    – Roaring Fish
    Oct 15, 2013 at 10:20
  • I have directed OP to Carillo's treatment of the issue - which is too long to go into properly here, and far more thorough than your answer, including instances where the 'normal'(!) comma'd version just wouldn't work* (see follow-on comment). It is important to read all that 4-part article. I did address the 'some native English speakers use the "-" sign to [add] some additional things in a sentence . . . [if I do this] Am I using the "-" correctly?' question.
    – Edwin Ashworth
    Oct 15, 2013 at 21:40
  • *See what happens when we use commas instead to punctuate [that] kind of parenthetical: “Their kindly uncle was terminally ill, they said they didn’t know it then, but his nephews and nieces just went on their merry ways.” The pauses provided by the two commas are much too brief to indicate the sudden shift from the major developing thought to the subordinate idea; structurally, they also truncate the sentence... (Carillo)
    – Edwin Ashworth
    Oct 15, 2013 at 21:41
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This piece of punctuation is called a dash. It is used to indicate a strong interruption in a sentence. In your example, a pair of commas would be the normal way to set off the non-defining relative clause. In general, you need a very good reason to use a pair of dashes.

From the advice of Larry Trask:

The dash has only one use: a pair of dashes separates a strong interruption from the rest of the sentence. (A strong interruption is one which violently disrupts the flow of the sentence.) Here are some examples:

  • An honest politician — if such a creature exists — would never agree to such a plan.
  • There was no other way — or was there?
  • John, do you suppose you could — oh, never mind; I'll do it.
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Sometimes the em dash is indicated by two hyphens together, like this: --.

I think em dashes might be used more widely in America than in England. Here you can use a pair of them just as you have done, instead of parentheses or instead of commas around an appositive. The difference between em dashes and those marks often seems insignificant to me, though the Chicago Manual says the dash indicates a more abrupt change of thought.

You can also use a single em dash instead of a colon:

"We ate them all: bread, crackers, and chips."

"We ate them all--bread, crackers, and chips."

I'd say the choice in all cases is a matter of personal style, though dashes get confusing if you use more than two in a sentence.

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  • Well they would be most differentiated in edited typeset text and least differentiated in handwritten text. In the middle in amateur electronic contexts like a forum or chat room it will be very inconsistent with some people using a single hyphen, some using two hyphens, some finding a way to enter an n- or m-dash, and also varying as to whether and when to put spaces before or after them.
    – hippietrail
    Oct 14, 2013 at 16:50

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