* Common Noun: When used to refer to a general concept of a river, it becomes a common noun. Example: "The Shannon is a major river in Ireland."
* Proper Noun: When referring to a specific person, river, or place named Shannon, it's a proper noun. Example: "My friend's name is Shannon." or "The River Shannon is known for its beauty."
It depends on the context to determine if "Shannon" is a common or proper noun.