What is a proper noun for each common noun?

A proper noun is a specific name that identifies a particular person, place, or organization, distinguishing it from common nouns, which are general names. For example, "city" (common noun) can be specified as "New York" (proper noun), "book" (common noun) can be "Harry Potter" (proper noun), and "company" (common noun) can refer to "Apple Inc." (proper noun). Proper nouns are typically capitalized to highlight their specificity.