Parenthetical expression includes information that may be helpful but is not essential to the meaning of a sentence. They are de-emphasize by

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being enclosed in parentheses (or sometimes dashes). While parenthetical expressions provide additional information, they can be removed from the sentence without altering the essential meaning.

To identify a parenthetical expression in a sentence, look for words or phrases that provide additional, but not crucial, information or clarification. These can be surrounded by parentheses, dashes, or commas. Sometimes, the expression is set off from the rest of the sentence by punctuation marks.

Here's an example:
- The weather (although it was predicted to be sunny) turned out to be rainy.

In this sentence, the expression "although it was predicted to be sunny" is a parenthetical expression. It provides additional information about the weather but can be removed without changing the essential meaning of the sentence.

It's important to note that parenthetical expressions are de-emphasized in writing. They are often used to provide supplemental information, but they are not crucial to the overall message or understanding of the sentence.