The dash is used, rather indiscriminately, for various purposes. It may replace a comma where a stronger break is required. It may be used in place of parentheses, the colon and the semicolon. Often it is used, in a rather informal or conversational style, to drop an interrupting phrase into a sentence.

A dash is not the same as a hyphen. It is used in a different way and it is longer than a hyphen. It may not be present on all keyboards, but you can create a dash by pressing the hyphen along with the ALT or OPTION key. This will give you an en dash (slightly longer than a hyphen). You can create an em dash (slightly longer still) by pressing the hyphen along with the SHIFT + ALT or OPTION key.

1. Interrupting Phrases

   An interrupting phrase may be an appositive, an example, or an explanatory aside.

   • The planet Saturn is very oblate – dash opening appositive adjective non-sphericalappositive adjective explaining what oblate means – dash closing appositive adjective because it rotates very fast.
   • A spore is made of just one part – dash opening appositive noun phrase a single cellappositive noun phrase – dash closing appositive noun phrase while a seed contains many cells, each with different jobs to do.

     This appositive noun phrase would be just as happy resting between two commas.

   • Small-world play – dash opening complex prepositional phrase such as with dolls houses or toy farm setscomplex prepositional phrase giving an example of "small-world play" – dash closing complex prepositional phrase can be used to help children learn to see things from other viewpoints and understand differences in spatial scale. 
   • Imagine you place a heavy bowling ball in the centre of a trampoline – dash opening an independent clause its mass bends the fabric, and it creates a dipindependent clause giving more information about the previous clause - a colon would serve just as well as a dash to introduce this.  
    
   

2. Coordinated Clauses

   • It’s easier for gametophytes to join together when its wet – dash opening a coordinated clause (a comma would serve just as well) and that’s why plants that use spores usually need to grow in wet placescoordinated clause introduced with the coordinator 'and'.
   • Modern life is full of distractions – dash opening a coordinated clause and some of them can have a negative effect on our ability to concentrate when studyingcoordinated clause introduced with the coordinator 'and'.
   • Ultra-processed foods are designed to be hyper-palatable – dash opening a coordinated clause and together with persuasive marketing, this can make resisting them an enormous challenge for some peoplecoordinated clause introduced with the coordinator 'and'.
    
   

3. Final Phrases

   Dashes are used to dive emphasis to a final word or phrase of a sentence.

   • Imagine how a drop of food coloring spreads in a glass of water – dash introducing final phrasethat’s diffusionfinal phrase.
   • Human impact spans the entire globe – dash introducing final phrase from the land to sea, and the south pole to the north polefinal phrase.
   • Ice is more reflective than water, and snow is extremely reflective – dash introducing final phrase more so than ice or waterfinal phrase.

Test your understanding of dash punctuation with the Dash Punctuation Quiz.

These examples were sourced from articles in The Conversation: Why are planets round?; Seeds; Spatial thinking; Gravity; How to avoid distractions; Ultra-processed foods; Why does nature create patterns?; Apex predators; Planet Rings

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