Without going too much into the nitty gritty and all the many rules that govern the use of punctuation, this post will help you to better understand when to use commas, dashes and brackets in your everyday writing.
Commas (,) = subordination
You use these to enclose words that form part of the flow of your sentence, words that don’t really need to stand out and which do not convey the most important information.
e.g. He is, and he knows it, brilliant.
The use of the commas in the above example says that first and foremost, ‘He’ is brilliant, and secondly, he knows it.
Dashes (–) = emphasis
When you want to highlight words and make them stand out, it’s best to surround them with dashes. These puncs create a bit of disturbance in the flow of your sentence, so be sure the words between them are worth the drama.
e.g. Darlene – innocent, timid Darlene – was behind the whole mess.
Most important info here? Darlene is known as ‘innocent’ and ‘timid’. Secondly, she was behind the whole mess.
Brackets / parenthesis ( ) = understating
When words feel a bit out of place in a sentence, but you’d like to make the info known, enclose them in brackets. These guys are great for including any extra info, like dates or side comments, in your sentence.
e.g. I’m going out tonight (second date!), but I’ll phone you tomorrow.
The Night Flight (also called the Star run) is cancelled.
Firstly, s/he is going out tonight and will phone the person on the other end of the message tomorrow. That s/he is going on a second date is a side comment, as it falls out of the flow of the sentence and is extra info.
The Night Flight being cancelled is the important info to be conveyed, that it is also called the Star run is additional info.
REMEMBER! Dashes and brackets have opposite effects. Dashes highlight and emphasise, brackets understate.