* Common nouns refer to general things or concepts. They are not capitalized unless they are at the beginning of a sentence.
* Proper nouns are specific names of people, places, or things. They are always capitalized.
Examples:
* Common noun: The surf was high today.
* Proper noun: I visited Hawaii to go surfing.
In the first sentence, "surf" refers to the general concept of waves breaking on the shore. In the second sentence, "Hawaii" is a specific place name and is therefore capitalized.