Capitalization Rules in English: A Practical Guide

The basic rules

English capitalizes the first word of every sentence, the pronoun I, proper nouns and the main words of titles. These four rules cover most of what you write. The first word of a sentence is capitalized, including the first word of a quotation that is a full sentence: She said, "We start at nine." The pronoun I is always a capital letter, also in contractions such as I'm and I'll.

Everything else is a refinement. Proper nouns name a specific person, place, organization or thing, and common nouns do not. The rest of this guide goes through the areas where writers hesitate: names and titles, days and months, directions, school subjects, organizations and the words after a colon.

Proper nouns and common nouns

Capitalize the names of people, places and organizations: Maria Lopez, Lake Michigan, the European Union. Capitalize nationalities, languages and religions: French, Spanish, Buddhist. Capitalize the names of specific events and historical periods: World War II, the Industrial Revolution. Brand names are capitalized as the brand spells them: iPhone, eBay, LinkedIn.

A common noun is not capitalized: a river, a company, a war. When it forms part of a name, it is capitalized: the Mississippi River, Acme Corporation. In the plural form it is lowercase again: the Mississippi and Missouri rivers. This rule explains most of the cases in which writers wonder whether to use a capital letter.

Titles of people

A job title is capitalized when it comes directly before a name and is used as part of the name: President Lincoln, Professor Chen, Dr. Patel. It is lowercase when it follows the name or stands alone: Abraham Lincoln, the president; Ms. Chen, a professor at the university. In formal documents, some organizations capitalize the title of their own officers, such as the Chief Executive Officer, but style guides such as Chicago and AP recommend lowercase unless the title is directly before a name.

Family words are capitalized when they serve as a name: I told Mom about it. They are lowercase when a possessive comes before them: I told my mom about it. The same test works for words such as Grandma, Uncle and Aunt.

Days, months, seasons and directions

The days of the week and the months of the year are capitalized in English: Monday, October. Holidays are capitalized too: Thanksgiving, Independence Day. The seasons are not: spring, summer, autumn, winter, unless they are part of a name, such as the Winter Olympics.

Compass directions are lowercase when they show direction, as in drive north, and capitalized when they name a region: the South, the Midwest, the Far East. School subjects are lowercase except for languages and for the names of specific courses: I study history and Spanish; she enrolled in Biology 101.

Titles of works and headings

The titles of books, films, songs and articles use title case, which capitalizes the main words and lowercases articles, short conjunctions and prepositions. The exact line between big and small words depends on the style guide. The article on title case rules compares APA, AP, Chicago and MLA, and the one on what title case is explains the basics.

Headings inside documents can use title case or sentence case. Pick one and apply it throughout. Many technology companies prefer sentence case for headings, and many publishers prefer title case. The article on sentence case versus title case has the trade-offs.

After a colon, in lists and in quotations

After a colon, capitalize the next word if it begins a complete sentence in AP style, and keep it lowercase if it begins a fragment: The rule is simple: capitalize the first word of a complete sentence. The Chicago Manual of Style capitalizes after a colon only if what follows is two or more complete sentences. Check your style guide, because the two differ.

The items of a vertical list start with a capital letter if they are complete sentences, and with a lowercase letter if they continue the sentence that introduces the list, often with a semicolon or comma at the end. A quotation starts with a capital letter if it is a full sentence on its own, and lowercase if it continues your sentence: He called the plan "a mistake from the start."

Common mistakes and how to avoid them

The most common mistakes are capitalizing words for emphasis (Important, Please Note), capitalizing common nouns that feel important (the Company, the Customer), writing seasons in capitals, and lowercasing names after a person's first mention. Another is over-capitalizing job titles in running text, which makes a page look like a legal agreement.

Acronyms and initialisms keep their capitals in every context: NASA, FBI, PDF, HTML. Words that began as acronyms but became ordinary words, such as laser and radar, are written in lowercase. A simple method is to ask: is this word the name of one specific thing, or does it start a sentence or a title? If not, it is lowercase. Use a case converter when you have a block of text in the wrong case, and then restore proper nouns by hand. Run a spell checker, but remember that it cannot catch every capitalization mistake.