Should I use a comma before and after an appositive?

An appositive is a word or phrase that helps to further identify a noun. Often the appositive can be swapped with the noun it helps describe.

• Example 1: Manuel Picon, the former French President, visited the UK yesterday.
• Example 2: The former French President Manuel Picon visited the UK yesterday.

Notice that in the first example, we use commas around the appositive, but in the second example we don't. That's the trick here. If the appositive is essential to the meaning of the phrase then we don't have commas, i.e. in Example 2 if we remove "Manuel Picon" we don't know which former French President we're talking about. In Example 1, we know exactly who visited the UK, so we add commas around the appositive because it is non-essential.

In some cases it can be tricky to decide. For example, if I say: My sister, Mary, will come then I may or may not use commas depending on the context. If I have several sisters and it is unclear which one will come without the appositive then I should not use commas. If I have only one sister then I should use commas. Just consider whether the meaning is unclear if the appositive is removed and if it is then don't use commas.