It's happening more and more isn't it? I wonder if it won't become an accepted usage in years to come. At the moment, although it's a popular way to use a dash, it's not correct. As you say, they're being used where commas should be used.

There IS a similarity in the way these double dashes are used and commas are used when interrupting a sentence. The only difference really is the level or the power of the interruption...Which is pretty subjective.

Dashes are used in a few ways, but to answer this specific question:

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.) Again, note that word `pair': in principle, at least, dashes come in pairs, though sometimes one of them is not written. (Remember that the same thing is true of bracketing commas, which set off weak interruptions.) Here are some examples:

An honest politician - if such a creature exists - would never agree to such a plan.

The destruction of Guernica - and there is no doubt that the destruction was deliberate - horrified the world.

When the Europeans settled in Tasmania, they inflicted genocide - there is no other word for it - upon the indigenous population, who were wiped out in thirty years.

If the strong interruption comes at the end of the sentence, then of course only one dash is used:

In 1453 Sultan Mehmed finally took Constantinople - and the Byzantine Empire disappeared from the map forever.

There was no other way - or was there?

In the case in which the original sentence is never resumed after the interruption, only one dash is used:

John, do you suppose you could - oh, never mind; I'll do it.

This sort of broken sentence is only found in representations of conversation, such as you might find in a novel; it is never appropriate in formal writing.

Hope that helps!

These two get in such a muddle. They're practically identical twins, but they DO have their own personalities and we should respect that!

• A hyphen click the 'line' button on the keyboard once: -
• A dash click twice: —

*many keyboards are different as are the processing programs used, so take a couple of moments to identify the short and long bars.

There are two types of dash: an 'en dash' (-)and an 'em dash'(—), known simply because of the length of the dash. The bar for the en dash is the same length as the letter n and that of the em dash, the letter m.

Although they all look very similar, they have very different uses:

The Hyphen

Used to divide words or join words.

If you have to split a word over two lines, put a hyphen at the end of a line between the syllables.

The film I watched last week was very ex-

citing, with lots of twists and turns.

Use a hyphen to join words, or join prefixes and words.

• He has a lot of self-confidence.
• My three-year-old is very energetic.
• My boss is very easy-going.
• Our records are finally up-to-date.

When it comes to joining words together there is a fair amount of leeway. Consider each word on its own merit: recreation and re-creation, unionized and un-ionized. If there can be some kind of mis-interpretation or the word looks clumsy without a hyphen, then add one. Think about how the phrase fits into the sentence great grandmother has a different meaning to great-grandmother.

The hyphen really is a helpful little chap, very willing to ensure your words don't muddle your reader; let him do his job!

Em Dash/Long Dash

The em dash is used to emphasis a point at the end of a sentence, it also has the same purpose as rounded brackets or bracketing commas within a sentence (to add a surprising point or a sudden change of thought):

• I'll meet you tonight at eight o'clock — if I can get out.
• An honest politian — if there is such a thing — would never agree to such a plan.

En Dash/Short Dash

Used to link numbers and words that are separate entities (not create a new word as the hyphen does):

• Michael Jackson (1958-2009) was known as The King of Pop
• The Thatcher-Reagan years were less than ideal socially.

Some publishing houses are now losing the distinction between the em (long) and en (short) dashes; there is also a move to reduce the number hyphens as well, but guage for yourself whether you feel you need — or want — it!