# What is this use of the dash?

The sentence is

The periodic table proposed by Mendeleev was the culmination of many observations and discoveries — but, like every culmination, this end was also a beginning.

I learnt that the dash is used to indicate a parenthetical element and that it is to be used in pairs. When only one is used, is it still to indicate a parenthetical element or is it something else?

• Yes, it's a parenthetical--a supplement--but it's not closed with a matching dash because the sentence comes to an end without resuming at the matrix level. Jan 18, 2017 at 5:37
• I see, so if the parenthetical element is at the end then it doesn't have to be closed with a dash. Jan 18, 2017 at 5:50
• I don't see a dash in that sentence. Jan 24, 2018 at 0:40
• In this case, it's there purely for emphasis. Take it out, and how does the meaning of ther passage change? You must be very, very careful about dashes in English writing. Any number of people will pop out of the woodwork to explain "rules" for using various different dashes but most of them won't see that Joe Average doesn't understand the question, let alone care about the answer. Apr 8, 2018 at 16:16

Yes, the dash functions the same in this sentence as it would in any situation with a pair, it is very much the same as finishing a sentence with brackets but brackets look out of place without closing them and therefore it is never seen with just one bracket.

In this case, the em dash is taking the place of a semicolon, possibly providing slightly more emphasis on the break:

The periodic table proposed by Mendeleev was the culmination of many observations and discoveries; but, like every culmination, this end was also a beginning.

The periodic table proposed by Mendeleev was the culmination of many observations and discoveries — but, like every culmination, this end was also a beginning.

In general, the em dash is fairly versatile. It can take the place of commas, parentheses, colons, and semicolons. The trick is not overusing them. There's a reason that the standard punctuation marks exist, and in most cases, it's best to use them.