What are Parentheses?
Parentheses are commonly used to set off information within a paragraph or text and provide more details to the preceding statement or paragraph. They are used in pairs and are a huge mainstay in many writings.
Brackets (or square brackets) are used when you intentionally include additional words to a quote. This might be necessary in cases where additional information will make for better understanding of the quote. For example, if you quote the sentence:
"It is always better in the morning."
There's likely not much that can be inferred from the sentence apart from its literal meaning. However, you may want to include more information to make the context clearer. This additional information should be enclosed in square brackets.
Thus, the statement can be further expounded:
"It is always better [to have your breakfast early] in the morning."
Failing to include this bracket results in a misquote, and this can be a serious pitfall if sensitive information were misquoted.
Parentheses or Brackets With Surrounding Punctuation
It is always best practice to make a distinction between parenthetical elements and the words making the rest of a sentence. This way, the sentence will still make sense even in the absence of the parenthetical elements. For example:
"Peter (just left for home) not long ago" surely doesn't read right if the words in parentheses are removed.
So it would make more sense to express as:
"Peter just left (for home) not long ago."
When dealing with question marks, periods and exclamation points, they should all go outside the parentheses or brackets, except in rare situations where these punctuation marks belong to the parenthetical elements. So you should never put a comma or other punctuation marks immediately before closing a parenthesis.
Thus; the following sentences are wrong:
Having played today, (the whole 90 minutes of the match), Paul arrived home visibly tired.
Having played today (the whole 90 minutes of the match,), Paul arrived home visibly tired.
The correct sentence is:
Having played today (the whole 90 minutes of the match), Paul arrived home visibly tired.