The/A and a Person's Name

Here's another post on the proper use of articles. Normally, we omit the articles the and a when we're using a person's name. We certainly do not say "I saw the Peter yesterday," or "A Margaret, who is my best friend, was in school with me."

However, there are cases when the/a can be used with proper names. These have something to do with pointing out specific persons who many have the same names as others. Consider these:

"The Peter I know would never cheat in a test." This sentence refers to a person called Peter, perhaps in reference to other persons called Peter (who might cheat on a test). The speaker here is certain that the Peter she knows is not a cheat.

"A Margaret from the office left a message for you." Here, Margaret is one woman from the office. There could be others but this particular woman may or may not be known to the receiver of the message. It could be a specific Margaret who is in-charge of certain messages.

"You met Piolo Pascual? The Piolo Pascual?" Here, the is used to emphasize a famous person.

We can't say "I saw the Peter yesterday" because the speaker is already talking about a specific Peter (there are no other Peters). We can't say "A Margaret, who is my best friend" either because there is already a specific Margaret (the best friend).