Grammar basics: A noun is a person, a place, or a thing. A proper noun is a subset of noun, referring to specific people, places, or things. This specificity leads to the key qualifiers of a proper noun; it refers to something unique, or one-of-a-kind, and is therefore capitalized.
For example, the "Taj Mahal" is a place (and arguably a thing), but as it is the only one in the world, it’s capitalized, making it a proper noun.
People's names are also proper nouns. Sure, there may be more than one "Sandra" or "Jack" in the world, but there's only one specific Sandra who sits next to you at work.
Let's dig into this grammar rule further.
The Difference Between Common Nouns and Proper Nouns
Non-proper nouns are called common nouns and do not reference one specific or unique thing. For example, “I feel like eating a cookie.” This sentence features a common noun, "cookie." To use a proper noun, try “I feel like eating an Oreo.” "Oreo" is a unique classification within the category of cookie.
Another type of cookie, perhaps an oatmeal cookie, would not be capitalized. The adjective "oatmeal" is adding a descriptor, but it's not calling out a specific, one-of-a-kind cookie, so "oatmeal cookie" is still a common noun.
Are Proper Nouns Always Capitalized?
Almost always, yes — that’s part of what makes a proper noun proper. There could be a trademarked product or company with a lowercase name, or perhaps someone chooses to spell their name with a lowercase letter. Those nouns are still proper, even though they are not capitalized.
However, some words can function as both common and proper nouns, depending on the context. For example, “We went swimming with dolphins on our vacation,” versus, “I hope the Dolphins win this weekend.” Here we’re talking about a common noun (dolphins as a species) versus a proper noun (the Miami Dolphins football team).
Are Titles Proper Nouns?
If you are pairing a title with someone’s name, you will generally capitalize it. You would capitalize President Bush as a proper noun, but “The president of Walmart will be visiting the warehouse next week,” would use a lowercase title. Same goes for, “The doctor will see you now,” versus, “Doctor Banner gave me a prescription to fill.”
What About Eponyms?
An "eponym" refers to a noun named after someone, or derived from a proper noun. Some eponyms are capitalized, some are not. Again, the difference between caps and non-caps comes down to being unique or specific. The word "sandwich" is an eponym named after the fourth Earl of Sandwich in the mid-18th century. While it was named for him, the noun "sandwich" is so broadly used, it’s no longer capitalized.
"Marxism" is a school of thought named after German political theorist Karl Marx. Because this body of teachings specifically relates to one person (Marx) and no one else, it’s capitalized.
Are There Any Outliers?
As with most of the English language, there are exceptions to every rule. For example, we capitalize the days of the week and months of the year, but do not capitalize the seasons, unless they're part of a formal name, as in "Winter Olympics."
Looking to the heavens, all of our celestial bodies are capitalized, while "sun" and "moon" generally are not, because there's more than one sun and moon in the universe. Earth is another one of those names that functions as both a common and proper noun. “She dug into the earth,” compared to, “The Earth is the third planet from the sun.”
These rules are really only suggestions. If a style guide or publication wants to capitalize certain nouns, they can make a decision and just stick to it.
Photo credit: Sylwia Bartyzel/ Unsplash