When is a proper noun preceded by an article?

Proper nouns are typically not preceded by articles. Some exceptions occur when the proper noun is being used in a specific sense, such as a nickname or title, or when the proper noun is being used to refer to a general category of things. For example:

- "The Beatles" is a proper noun referring to the musical group, but "the Beatles" is also used to refer to a genre of music.

- "President Obama" is a proper noun referring to a specific person, but "the president" is also used to refer to any president in a general sense.