Subscript and superscript

This article is about the terms 'subscript' and 'superscript' as used in typography. "SuperScript" can also refer to a commercially available Reverse transcriptase.

A subscript or superscript is a number, figure, symbol, or indicator that appears smaller than the normal line of type and is set slightly below or above it – subscripts appear at or below the baseline, while superscripts are above. Subscripts and superscripts are perhaps best known for their use in formulas, mathematical expressions, and descriptions of chemical compounds or isotopes, but have many other uses as well.

In professional typography, subscript and superscript characters are not simply ordinary characters reduced in size; to keep them visually similar to the rest of the font, typeface designers make them slightly heavier than a reduced-size character would be. Likewise, the amount that sub- or superscripted text is moved from the original baseline varies by typeface and by use.

Uses

A single typeface may contain sub- and super-script glyphs at different positions for different uses. The four most common positions are listed here. Because each position is used in different contexts, not all alphanumerics may be available in all positions. For example, subscript letters on the baseline are quite rare, and many typefaces only provide a limited number of superscripted letters. Despite these differences, all reduced-sized glyphs go by the same generic name of subscript and superscript. Note that the terms subscript and superscript are synonymous with the terms inferior letter (or number) and superior letter (or number), respectively.

Subscripts which are dropped below the baseline

Perhaps the most familiar example of subscripts is in chemical formulas. For example, the formula for glucose is C₆H₁₂O₆, meaning that it is a molecule with 6 carbon atoms, 12 hydrogen atoms and six oxygen atoms.

A subscript can also distinguish between different versions of a subatomic particle. Thus electron, muon, and tau neutrinos are denoted and . A particle may be distinguished by multiple subscripts, such as for the triple bottom omega particle.

Similarly, subscripts are also used frequently in mathematics to define different versions of the same variable; for example, in an equation x₀ and x_f may indicate the initial and final value of x, while v_rocket and v_observer would stand for the velocities of a rocket and an observer. In addition to this, subscript can be use to refer to members in a sequence or set. For example, in the sequence O = (45, -2, 800), O₃ refers to the third member of sequence O, which is 800.

Also in mathematics and computing, subscript can be used to represent the radix, or base, of a written number, especially where multiple bases are used alongside each other. For example, comparing values in hexadecimal, denary, and octal one might write C_hex = 12_dec = 14_oct.

Subscripted numbers dropped below the baseline are also used for the denominators of stacked fractions, like this: $tfrac\{67\}\{68\}$.

Subscripts which are aligned with the baseline

The only common use of these subscripts is for the denominators of diagonal fractions, like ½ or the signs for percent %, permille ‰, and basis point ‱. Certain standard abbreviations are also composed as diagonal fractions, such as ℅ (care of), ℀ (account of), ℁ (addressed to the subject), or in Spanish ℆ (cada uno/a, "each one").

Superscripts which typically do not extend above the ascender line

These superscripts typically share a baseline with numerator digits, the top of which are aligned with the top of the full-height numerals of the base font; lower-case ascenders may extend above. See also: superior letter.

Ordinal indicators are sometimes written as superscripts (1^st, 2^nd, 3^rd rather than 1st, 2nd, 3rd), although many English-language style guides recommend against this use. Other languages use a similar convention, such as 1^er or 2^e in French, or 4ª and 4º in Italian, Portuguese, and Spanish.

Many abbreviations use superscripts, especially historically. Examples in English include J^os and W^m (for Joseph and William), y^e (for the, originally þe), th^t or y^t (that), y^r (your), or ma^ty (majesty) In handwritten shorthand, many abbreviations are still written this way, such as defⁿ (definition), exp^t (experiment), or gov^t (government). In French, superscript abbreviations are still quite common, such as M^lle (for Mademoiselle) and G^le (for générale). The standard abbreviation for “number,” №, also uses a superscript. In early modern writing, two-letter abbreviations were sometimes written with the superscript directly above the base letter, as in yͤ or yͭ.

In early Middle High German, umlauts and other modifications to pronunciation would be indicated by superscript letters placed directly above the letter they modified. Thus the modern umlaut ü was written as uͤ; both vowel and consonants were used in this way, as in ſheͨzze or boͮsen In modern typefaces, these letters are usually smaller than other superscripts, and their baseline is slightly above the base font’s midline, making them extend no higher than a typical ordinal indicator.

Superscripts are used for the standard abbreviations for service mark ℠ and trademark ™. The signs for copyright © and registered trademark ® are also sometimes superscripted, depending on the use or the typeface.

On hand-written documents and signs, a monetary amount may be written with the cents value superscripted, as in $8⁰⁰ or 8€⁵⁰. Often the superscripted numbers will be underlined: $8⁰⁰, 8€⁵⁰. The currency sign itself may also be superscripted, as in ^$80 or 6^¢.

Superscripted numerals are used for the numerators of diagonal fractions, like ¾ or the signs for percent %, permille ‰, and basis point ‱. Certain standard abbreviations are also composed as diagonal fractions, such as ℅ (care of), ℀ (account of), ℁ (addressed to the subject), or in Spanish ℆ (cada uno/a, "each one").

Superscripts which typically extend above the ascender line

Both low and high superscripts can be used to indicate the presence of a footnote in a document, like this⁵ or this.^xi Any combination of characters can be used for this purpose; in technical writing footnotes are sometimes composed of letters and numbers together, like this.^A.2 The choice of low or high alignment depends on one’s taste, but high-set footnotes tend to be more common, as they stand out more from the text.

In mathematics, high superscripts are used to indicate that one number or variable is raised to the power of another number or variable. Thus y⁴ is y raised to the fourth power, 2^x is 2 raised to the power of x, and the famous equation E = mc² includes a term for the speed of light squared.

The charges of ions and subatomic particles are also denoted with superscripts. is a negatively charged chlorine atom, is an atom of lead with a charge of positive four, is an electron, is a positron, and is an antimuon.

Atomic isotopes are written using superscripts. In symbolic form, the number of nucleons is denoted as a superscripted prefix to the chemical symbol (for example , , , , and ). The letters m or f may follow the number to indicate metastable or fission isomers, as in or

Subscripts and superscripts can also be used together to give more specific information about nuclides. For example, denotes an atom of uranium with 235 nucleons, 92 of which are protons. A chemical symbol can be completely surrounded: is an ion of carbon with 14 nucleons, of which six are protons and 8 are neutrons.

The numerators of stacked fractions (such as $tfrac\{34\}\{35\}$) usually use high-set superscripts, although some specially designed glyphs keep the top of the numerator aligned with the top of the full-height numerals.

Alignment examples

This image shows the four common locations for subscripts and superscripts, according to their typical uses. The typeface is Minion Pro, set in Adobe Illustrator. Note that the default superscripting algorithms of most word processors would set the “th” and “lle” too high, and the weight of all the subscript and superscript glyphs would be too light.

Software support

Desktop publishing

Many text editing and word processing programs have automatic subscripting and superscripting features, although these programs usually simply use ordinary characters reduced in size and moved up or down – they are not true subscript or superscript glyphs. Professional typesetting programs such as QuarkXPress or Adobe InDesign also have similar features for automatically converting regular type to subscript or superscript. These programs, however, may also offer native OpenType support for the special subscript and superscript glyphs included in many professional typeface packages (such as those shown in the image above). See also OpenType, below.

Comparison of software support
Software	OpenType support for professional glyphs?	Default values for glyph transformation (non-professional glyphs)				Keyboard Shortcuts
		size	subscript position	superscript position	user-modifiable settings?	subscript	superscript
OpenOffice 2.3	no	58%	-33%	+33%	yes	CTRL+SHIFT+b	CTRL+SHIFT+p
Microsoft Word 2002	no	65%	-14.1%	+35%	manual1	CTRL+=	CTRL+SHIFT+=
Adobe Illustrator CS3	yes	58.3%	-33.3%	+33.3%	yes
Adobe Photoshop CS3	ordinal letters only	58.3%	-33.3%	+33.3%	manual1	ALT+CTRL+SHIFT+=	CTRL+SHIFT+=
Notes: 1. Default subscript and superscript options can be overcome by manually changing the font size and raising/lowering text.

HTML subscripts and superscripts
Ab Cd

HTML

In HTML and Wiki syntax, subscript text is produced by putting it inside the tags <sub> and </sub>. Similarly, superscripts are produced with and . The exact size and position of the resulting characters will vary by font and browser, but are usually reduced to around 75% original size. Note that superscripts are usually placed too high for many typographic purposes.

TeX

In TeX's mathematics mode (as used in MediaWiki), subscripts are typeset with the underscore, while superscripts are made with the caret. Thus $X_{ab}$ produces $X\_\{ab\}$, and $X^{ab}$ produces $X^\{ab\}$.

Unicode

Unicode defines subscript and superscript characters in several areas. Note, however, that fonts which include these characters may align them quite differently: subscripts may be at or below the baseline, while superscripts may stop at the cap line or extend above it. The same font may even align letters and numbers in different ways. Because of these inconsistencies, these glyphs may not be suitable for some purposes (see Uses, above).

Unicode includes subscript and superscript characters in the following blocks:

• the Latin-1 Supplement block contains the feminine and masculine ordinal indicators ª and º, superscript numerals ¹, ², and ³, the permille sign ‰, and the precomposed diagonal fractions ½, ¼, and ¾. The copyright © and registered trademark signs ® are also in this block.
• the General Punctuation block contains the permille sign ‰ and the per-ten-thousand sign ‱.
• the Number Forms block contains several pre-composed diagonal fractions: ⅓ ⅔ ⅕ ⅖ ⅗ ⅘ ⅙ ⅚ ⅛ ⅜ ⅝ ⅞ ⅟
• the Combining Diacritical Marks block contains medieval superscript letter diacritics. These letters are written directly above other letters appearing in medieval Germanic manuscripts, and so these glyphs do not include spacing, for example uͤ. They are shown here over a long string of periods: ....ͣ...ͤ...ͥ...ͦ...ͧ...ͨ...ͩ...ͪ...ͫ...ͬ...ͭ...ͮ...ͯ..
• the Subscripts and Superscripts block contains superscripts of numbers, mathematical symbols, and a few letters: ⁰ ⁱ ⁴ ⁵ ⁶ ⁷ ⁸ ⁹ ⁺ ⁻ ⁼ ⁽ ⁾ ⁿ ₀ ₁ ₂ ₃ ₄ ₅ ₆ ₇ ₈ ₉ ₊ ₋ ₌ ₍ ₎ ₐ ₑ ₒ ₓ ₔ
• the Letterlike Symbols block contains a few symbols composed of subscript and superscript characters: ℀ ℁ ℅ ℆ № ℠ ™
• the Spacing Modifier Letters block has superscripted letters and symbols used for phonetic transcription: ʰ ʱ ʲ ʳ ʴ ʵ ʶ ʷ ʸ ˀ ˁ ˠ ˡ ˢ ˣ ˤ
• the Phonetic Extensions block has several sub- and super-scripted letters and symbols: ᴬ ᴭ ᴮ ᴯ ᴰ ᴱ ᴲ ᴳ ᴴ ᴵ ᴶ ᴷ ᴸ ᴹ ᴺ ᴻ ᴼ ᴽ ᴾ ᴿ ᵀ ᵁ ᵂ ᵃ ᵄ ᵅ ᵆ ᵇ ᵈ ᵉ ᵊ ᵋ ᵌ ᵍ ᵎ ᵏ ᵐ ᵑ ᵒ ᵓ ᵔ ᵕ ᵖ ᵗ ᵘ ᵙ ᵚ ᵛ ᵜ ᵝ ᵞ ᵟ ᵠ ᵡ ᵢ ᵣ ᵤ ᵥ ᵦ ᵧ ᵨ ᵩ ᵪ ᵸ
• the Phonetic Extensions Supplement block has a few more: ᶛ ᶜ ᶝ ᶞ ᶟ ᶠ ᶡ ᶢ ᶣ ᶤ ᶥ ᶦ ᶧ ᶨ ᶩ ᶪ ᶫ ᶬ ᶭ ᶮ ᶯ ᶰ ᶱ ᶲ ᶳ ᶴ ᶵ ᶶ ᶷ ᶸ ᶹ ᶺ ᶻ ᶼ ᶽ ᶾ ᶿ

Consolidated for cut-and-pasting purposes, the Unicode standard defines complete sub- and super-scripts for numbers and common mathematical symbols (⁰ ¹ ² ³ ⁴ ⁵ ⁶ ⁷ ⁸ ⁹ ⁺ ⁻ ⁼ ⁽ ⁾ ₀ ₁ ₂ ₃ ₄ ₅ ₆ ₇ ₈ ₉ ₊ ₋ ₌ ₍ ₎ ), a full superscript latin lowercase alphabet except q (ᵃ ᵇ ᶜ ᵈ ᵉ ᶠ ᵍ ʰ ⁱ ʲ ᵏ ˡ ᵐ ⁿ ᵒ ᵖ ʳ ˢ ᵗ ᵘ ᵛ ʷ ˣ ʸ ᶻ ), a limited uppercase latin alphabet (ᴬ ᴮ ᴰ ᴱ ᴳ ᴴ ᴵ ᴶ ᴷ ᴸ ᴹ ᴺ ᴼ ᴾ ᴿ ᵀ ᵁ ᵂ ), a few subscripted lowercase letters (ₐ ₑ ᵢ ₒ ᵣ ᵤ ᵥ ₓ ), and some greek letters (ᵅ ᵝ ᵞ ᵟ ᵋ ᶿ ᶥ ᶲ ᵠ ᵡ ᵦ ᵧ ᵨ ᵩ ᵪ ). Note that since these glpyhs come from different ranges, they may not be of the same size and position, depending on the typeface.

OpenType

One of the advanced features of OpenType typefaces is support for professionally designed subscript and superscript glyphs. Exactly which glyphs are included varies by typeface; some have only basic support for numerals, while others contain a full set of letters, numerals, and punctuation. Since many of these glyphs are not included in Unicode, they are typically placed in the Unicode Private Use Area.

See also

• Mathematical notation
• Typographical conventions in mathematical formulae
• Superior letter
• Furigana
• Ruby character
• Typesetting
• Font

External links

• Vincent Connare’s type-design standards for Microsoft
• Vertical alignment questions from Typophile.com