A proper noun is the specific name of a unique person, place, organization, or thing. Proper nouns identify one particular entity rather than a general category. In English, proper nouns are written with an initial capital letter. Common nouns refer to general categories and are not capitalized unless they begin a sentence.

Proper nouns include names of people, places such as cities and countries, organizations and institutions, and titles of works. Days of the week, months, holidays, and languages are also treated as proper nouns in English. The category determines what counts as a unique name to be capitalized.

Word/Phrase	Definition
names	A specific person or group of people is a proper noun.
places	A specific geographic location is a proper noun.
organizations	A specific group, institution, or company is a proper noun.
titles	The specific name of a book, work, or event is a proper noun.
days and months	The names of days and months are proper nouns in English.

In English, the first letter of each proper noun is capitalized. In multi-word proper nouns, each main word is usually capitalized, including names of people and most words in place names. Articles and short connectors within titles may follow specific style guides but do not change the status of the proper noun. The rule applies regardless of sentence position.

Rule
Capitalize the first letter of a proper noun.
Capitalize each main word in a multi-word proper noun.
Do not lowercase a proper noun because it appears in the middle of a sentence.

Common nouns name general categories such as city, river, or company, while proper nouns give the specific name such as London, Nile, or Google. The same word can function as common or proper depending on whether it names a unique entity. Capitalization signals that the word is being used as a proper noun in context.

Word/Phrase	Definition
city	A general category is a common noun and is not capitalized.
London	The specific name of a city is a proper noun and is capitalized.
river	A general term for rivers is a common noun.
Nile	The name of a particular river is a proper noun.
company	A general term for businesses is a common noun.
Google	The name of a specific company is a proper noun.

Proper nouns can appear as subjects, objects, or possessives without changing their capitalization. In possessive forms, the proper noun remains capitalized and the possessive marker is added. When a common noun is part of an official name, the whole name is treated as a proper noun and capitalized accordingly.

Rule
Keep the initial capital in a proper noun when forming the possessive.
Capitalize official names that include common nouns as part of the full name.
Do not capitalize a common noun unless it begins a sentence or is part of a full proper name.

Proper nouns are specific names and are capitalized in English. Recognizing the category and context helps distinguish proper nouns from common nouns. Consistent capitalization marks the word as a unique reference in writing.