Letter case

Letter case is the distinction between the letters that are in larger uppercase or capitals and smaller lowercase in the written representation of certain languages. The writing systems that distinguish between the upper- and lowercase have two parallel sets of letters: each in the majuscule set has a counterpart in the minuscule set. Some counterpart letters have the same shape, and differ only in size, but for others the shapes are different. The two case variants are alternative representations of the same letter: they have the same name and pronunciation and are typically treated identically when sorting in alphabetical order.
Letter case is generally applied in a mixed-case fashion, with both upper and lowercase letters appearing in a given piece of text for legibility. The choice of case is often denoted by the grammar of a language or by the conventions of a particular discipline. In orthography, the uppercase is reserved for special purposes, such as the first letter of a sentence or of a proper noun, which makes lowercase more common in regular text.
In some contexts, it is conventional to use one case only. For example, engineering design drawings are typically labelled entirely in uppercase letters, which are easier to distinguish individually than the lowercase when space restrictions require very small lettering. In mathematics, on the other hand, uppercase and lowercase letters denote generally different mathematical objects, which may be related when the two cases of the same letter are used; for example, may denote an element of a set.

Terminology

The terms upper case and lower case may be written as two consecutive words, connected with a hyphen, or as a single word. These terms originated from the common layouts of the shallow drawers called type cases used to hold the movable type for letterpress printing. Traditionally, the capital letters were stored in a separate shallow tray or "case" that was located above the case that held the small letters.

Majuscule

Majuscule, for palaeographers, is technically any script whose letters have no or very few ascenders and descenders. Consequently, all of the letters of a majuscule script are of roughly the same height and it is written within the space of just two parallel lines. This is contrasted with the four lines required by a minuscule script, on which see below. While majuscule scripts were originally used to write entire texts, their letters eventually came to be used primarily with the modern function of uppercase letters in European writing, so the term may sometimes be used as a synonym of 'uppercase letter' or 'capital' in contemporary contexts.

Minuscule

Minuscule refers to lower-case letters. In paleography, the term refers to a script which includes letters of different heights, with ascenders and descenders, so it needs to be written within a space of four parallel lines. Minuscule script letters eventually came to be used with the function of lowercase letters in European writing.

Typographical considerations

The glyphs of lowercase letters can resemble smaller forms of the uppercase glyphs restricted to the baseband or can look hardly related. Here is a comparison of the upper and lower case variants of each letter included in the English alphabet :
Typographically, the basic difference between the majuscules and minuscules is not that the majuscules are big and minuscules small, but that the majuscules generally are of uniform height.
There is more variation in the height of the minuscules, as some of them have parts higher or lower than the typical size. Normally, b, d, f, h, k, l, t are the letters with ascenders, and g, j, p, q, y are the ones with descenders. In addition, with old-style numerals still used by some traditional or classical fonts, 6 and 8 make up the ascender set, and 3, 4, 5, 7, and 9 the descender set.

Bicameral script

A minority of writing systems use two separate cases. Such writing systems are called bicameral scripts. These scripts include the Latin, Cyrillic, Greek, Coptic, Armenian, Glagolitic, Adlam, Warang Citi, Old Hungarian, Garay, Zaghawa, Osage, Vithkuqi, and Deseret scripts. Languages written in these scripts use letter cases as an aid to clarity. The Georgian alphabet has several variants, and there were attempts to use them as different cases, but the modern written Georgian language does not distinguish case.
All other writing systems make no distinction between majuscules and minuscules a system called unicameral script or unicase. This includes most syllabic and other non-alphabetic scripts.
In scripts with a case distinction, lowercase is generally used for the majority of text; capitals are used for capitalisation and emphasis when boldface is not available. Acronyms are often written in all-caps, depending on various factors.

Capitalisation

Capitalisation is the writing of a word with its first letter in uppercase and the remaining letters in lowercase. Capitalisation rules vary by language and are often quite complex, but in most modern languages that have capitalisation, the first word of every sentence is capitalised, as are all proper nouns.
Capitalisation in English, in terms of the general orthographic rules independent of context, is universally standardised for formal writing. Capital letters are used as the first letter of a sentence, a proper noun, or a proper adjective. The names of the days of the week and the names of the months are also capitalised, as are the first-person pronoun "I" and the vocative particle "O". There are a few pairs of words of different meanings whose only difference is capitalisation of the first letter. Honorifics and personal titles showing rank or prestige are capitalised when used together with the name of the person or as a direct address, but normally not when used alone and in a more general sense. It can also be seen as customary to capitalise any word in some contexts even a pronoun referring to a deity.
Other words normally start with a lower-case letter. There are, however, situations where further capitalisation may be used to give added emphasis, for example in headings and publication titles. In some traditional forms of poetry, capitalisation has conventionally been used as a marker to indicate the beginning of a line of verse independent of any grammatical feature. In political writing, parody and satire, the unexpected emphasis afforded by otherwise ill-advised capitalisation is often used to great stylistic effect, such as in the case of George Orwell's Big Brother.
Other languages vary in their use of capitals. For example, in German all nouns are capitalised, while in Romance and most other European languages the names of the days of the week, the names of the months, and adjectives of nationality, religion, and so on normally begin with a lower-case letter. On the other hand, in some languages it is customary to capitalise formal polite pronouns, for example De, Dem, Sie, Ihnen, and Vd or Ud.
Informal communication, such as texting, instant messaging or a handwritten sticky note, may not bother to follow the conventions concerning capitalisation, but that is because its users usually do not expect it to be formal.

Exceptional letters and digraphs

The German letter "ß" formerly existed only in lower case. The orthographical capitalisation does not concern "ß", which generally does not occur at the beginning of a word, and in the all-caps style it has traditionally been replaced by the digraph "SS". Since June 2017, however, capital ẞ is accepted as an alternative in the all-caps style.
The Greek upper-case letter "Σ" has two different lower-case forms: "ς" in word-final position and "σ" elsewhere. In a similar manner, the Latin lower-case letter "S" used to have two different lower-case forms: "s" in word-final position and " ſ " elsewhere. The latter form, called the long s, fell out of general use before the middle of the 19th century, except in countries that continued to use blackletter typefaces such as Fraktur. When blackletter type fell out of general use in the mid-20th century, even those countries dropped the long s.
The treatment of the Greek iota subscript with upper-case letters is complicated.
Unlike most languages that use Latin-script and link the dotless upper-case "I" with the dotted lower-case "i", Turkish, Tatar, Crimean Tatar as well as Azeri in Azerbaijan have both a dotted and dotless I, each in both upper and lower case. The two pairs represent distinct phonemes.
In some languages, specific digraphs may be regarded as single letters, and in Dutch, the digraph "IJ/ij" is even capitalised with both components written in uppercase. In other languages, such as Welsh and Hungarian, various digraphs are regarded as single letters for collation purposes, but the second component of the digraph will still be written in lower case even if the first component is capitalised. Similarly, in South Slavic languages whose orthography is coordinated between the Cyrillic and Latin scripts, the Latin digraphs "ǈ/ǉ", "ǋ/ǌ" and "ǅ/ǆ" are each regarded as a single letter, but only in all-caps style should both components be in upper case. Unicode designates a single character for each case variant of the three digraphs.
Some English surnames such as fforbes are traditionally spelt with a digraph instead of a capital letter.
In the Hawaiian orthography, the okina is a phonemic symbol that visually resembles a left single quotation mark. Representing the glottal stop, the okina can be characterised as either a letter or a diacritic. As a unicase letter, the okina is unaffected by capitalisation; it is the following letter that is capitalised instead.