Capitalization is the practice of writing some letters in an uppercase (capital) form and others in a lowercase form. English uses a Latin-script convention in which certain words or letters are regularly capitalized: the first word of a sentence, the personal pronoun "I," proper names, acronyms and initialisms, and headings depending on style. Spelling differs regionally — for example, capitalize (North American) versus capitalise (British) — and the general notion can be expressed as changing characters to upper case or lower case (letters).

Common rules and conventions

Many languages and style guides give practical rules for when to capitalise. In English, typical cases include:

  • First word of a sentence or quoted sentence (sentence starts).
  • Names of people, organizations, places and specific works (proper nouns).
  • The pronoun "I" and the first word after certain punctuation marks.
  • Acronyms, initialisms and abbreviations (e.g., NASA, EU).
  • Headings and titles, which may follow "title case" or "sentence case" rules depending on a style manual.

Different languages apply capitalization differently. For instance, German is notable for capitalising all nouns; other languages may capitalise only the first word of a sentence or not use case distinctions at all (languages vary).

Variation, styles and exceptions

Style guides and typographic traditions affect how capitalization is used. "Title case" capitalizes most words in a headline, while "sentence case" capitalizes only the first word and proper names. Some brands choose idiosyncratic forms (all-lowercase or ALL-CAPS) for marketing. Punctuation, hyphenation and prepositions often determine whether a word is capitalized in title case. Legal documents, bibliographies and programming languages may apply stricter or different rules.

Historical development

Uppercase and lowercase forms grew out of ancient writing and medieval scripts. Early Latin inscriptions used only majuscule (capital) letterforms; later cursive and minuscule scripts developed distinct small letters to improve speed and legibility. The modern pairing of capitals for emphasis and lowercase for body text became established with the rise of printing and standard orthography.

Technical considerations

Computing introduces additional complexity: many systems are case-sensitive, so "File.txt" and "file.txt" can be distinct. Software libraries provide functions to convert case, but conversions must respect locale-specific rules. A famous example is the dotted and dotless forms of the letter "i" in Turkish, which require locale-aware handling. Unicode defines mappings for case conversion and case folding to support searching and normalization across scripts.

Some notable points: German’s practice of capitalising nouns makes it stand out among modern European languages, though capitalization traditions differ worldwide (German and other conventions). The verb "to capitalize" also has other meanings in English; it is a homonym that can mean to finance or convert income into capital (homonym), especially in business contexts (investment).

Understanding capitalization improves clarity, signals grammatical roles, and helps maintain conformity with readers’ expectations. In unfamiliar situations, consult a relevant style guide (for example, a journal, publisher or institutional manual) to learn whether to use sentence case, title case, or an alternative convention.