Capitalization rules tend to vary by language and can be quite complicated. It is widely understood that the first word of a sentence and all proper nouns are always capitalized. However, what is not so clear is the origin of the upper case distinction that has become common practice, especially in regards to Modern English. To unmask the origin of the capital letter we need to refer to a script derived from the Old Roman cursive called uncial.
Uncial is a majuscule script, a synonym meaning “large or capital letter,” commonly used by Latin and Greek scribes beginning around the 3rd century AD. The word is derived from the Latin uncialis meaning “of an inch, of an ounce.”
The first use of the word uncial, and thus the possible origin of its modern meaning, is from St. Jerome’s preface to the Book Of Job and the following passage: “Let those who so desire have old books, or books written in gold and silver on purple parchment, or burdens (rather than books) written in uncial letters, as they are popularly called.” It is believed that St. Jerome is referring to the uppercase letters within the text. In addition, as St. Jerome makes reference to – the move from the rough writing surface of papyrus to the smoother parchment and vellum made possible a more rounded single stroke writing style instead of the former angular, multiple stroke style.
The original twenty-one letters in the Latin alphabet are derived from the uncial style of writing. As the Latin alphabet was adapted for other languages over time, more letters were added that also incorporated the majuscule lettering thus giving us the Modern Latin alphabet from which the English alphabet is derived.
As the uncial script evolved, a smaller, more rounded and connected Greek-style lettering called minuscule was introduced around the 9th century AD. It soon became very common to mix miniscule and some uncial or capital letters within a word, the latter used to add emphasis. In contrast, many other writing systems such as the Georgian language and Arabic make no distinction between upper and lowercase lettering – a system called unicase.