In writing, you can show parenthesis in several different ways. You can, for example, use two brackets. You may also use two commas or two dashes.
Note that removing a parenthesis from the sentence will not create any ungrammaticality. Parentheses are essentially used to mark off words or phrases inserted into a sentence.
- Susie, my friend, accompanied me to school.
Here the writer employs two commas to mark off the phrase (my friend). Brackets and dashes are also possible in this case.
- Susie (my friend) accompanied me to school.
- Susie – my friend – accompanied me to school.
Brackets are preferred when the sentence already contains one or more commas.
- Last week, Charlie (a coast guard) saved four boys from drowning.
Here the writer employs brackets because the sentence already contains a comma.
Generally speaking, the conjunctive adverbs however, therefore, as a result, as far as concerned, subsequently, so to speak etc., are not usually used with brackets. Instead we use commas.
English has few vowel sounds. Some languages, on the other hand, use thirty or more.
Which one to use?
It is essentially your choice.
Brackets are easily seen and hardly create any confusion. However, you must limit their use. Too many brackets can make your writing look unorganized or even clumsy.
Commas look perfectly alright, but when you use commas as parenthesis, they might get confused with other commas in the sentence.
Dashes are mainly used in informal writing.