Markr.01891's comments

"Now consider the below sentences –

3. My friend, John, is a good painter.

4. My friend John is a good painter.

Both these sentences are correct and convey the same thing. The rule is – either have the commas both before and after a name, or don’t add it at all. This is because the sentence is talking about a particular person John. The addition of commas gives extra emphasis to the name."

These sentences do not convey the same thing.

The second example of 'My friend John is a good painter' is correct as the writer is talking about one of his/her friends out of several friends whose name is John. This is fine.

However, the second sentence of 'My friend, John, is a good painter' is different because the commas become appositive commas, and mean the writer is talking about his/her one and only friend who is called John. more »

If you write 'My twin brother Martin won a prize' then you are talking about one twin brother out of many. We can assume you only have one twin brother, so this would be the incorrect way to write it.

If you write 'My twin brother, Martin, won a prize', then you are using what's known as appositive commas, and in this case the meaning is that you are talking about your only twin brother, which would be correct. more »