Here's why:
* Common nouns refer to general categories or things. They are not specific to one particular person, place, or thing.
* Proper nouns are specific names of people, places, or things and are capitalized.
Since "literature" refers to the general concept of written works, it's a common noun.
However, if you're referring to a specific literary work (like "The Great Gatsby" or "Hamlet"), those would be proper nouns because they are specific names.