The term ‘parenthesis’ (or ‘parentheses’ in the plural) is commonly used as an alternative term for ‘brackets’.

In fact, parenthesis is the explanatory or additional wording that goes inside the brackets. And this information can be separated from the main text by a number of different punctuation marks: not just brackets, but also dashes, or, simply, commas.

So, which kind of punctuation should you choose? That’s partly determined by the degree of relevance of the parenthesis to the main clause. Consider the following sentences:

  1. The man, who made his fortune from cookies, was an expert baker.
  2. The man — who made his fortune from cookies — started out poor.
  3. The man (who made his fortune from cookies) was South African.

In sentence 1, we understand that there is a strong relationship between his skill as a baker and the fact that he made money from cookies. We use commas to show that there is no real separation of detail.

In sentence 2, the fact that he was originally poor is stressed, but the source of his fortune is not so important — it just happened to be cookies.

By the time we reach sentence 3, how he made his fortune is not at all relevant, and the brackets allow us to safely remove the information about the cookies from the main thrust of the sentence.

In all three cases, the sentence MUST still read correctly if we take out the parenthesis. This is a crucial test for proofreaders’ understanding of punctuation.