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A subscript or superscript is a character (such as a number or letter) that is set slightly below or above the normal line of type, respectively. It is usually smaller than the rest of the text. Subscripts appear at or below the baseline, while superscripts are above. Subscripts and superscripts are perhaps most often used in
formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the terminology, term ''formula'' in science refers to the Commensurability (philosophy o ...
s, mathematical expressions, and specifications of
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A homonuclear molecule, molecule co ...
s and
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbe ...
s, but have many other uses as well. In professional
typography Typography is the art and technique of typesetting, arranging type to make written language legibility, legible, readability, readable and beauty, appealing when displayed. The arrangement of type involves selecting typefaces, Point (typogra ...
, subscript and superscript characters are not simply ordinary characters reduced in size; to keep them visually consistent with the rest of the font, typeface designers make them slightly heavier (i.e. medium or bold typography) than a reduced-size character would be. The vertical distance that sub- or superscripted text is moved from the original baseline varies by typeface and by use. In typesetting, such types are traditionally called "superior" and "inferior" letters, figures, etc., or just "superiors" and "inferiors". In English, most nontechnical use of superiors is archaic. Superior and inferior figures on the baseline are used for
fraction A fraction (from la, fractus, "broken") represents a part of a whole or, more generally, any number of equal parts. When spoken in everyday English, a fraction describes how many parts of a certain size there are, for example, one-half, eight ...
s and most other purposes, while lowered inferior figures are needed for chemical and mathematical subscripts.


Uses

A single typeface may contain sub- and superscript 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 provide only a limited number of superscripted letters. Despite these differences, all reduced-size glyphs go by the same generic terms ''subscript'' and ''superscript'', which are synonymous with the terms ''inferior letter'' (or ''number'') and ''superior letter'' (or ''number''), respectively. Most fonts that contain superscript/subscript will have predetermined size and orientation that is dependent on the design of the font.


Subscripts that are dropped below the baseline

Perhaps the most familiar example of subscripts is in
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
s. For example, the chemical formula for
glucose Glucose is a simple sugar with the Chemical formula#Molecular formula, molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis f ...
is C6 H12 O6 (meaning that it is a molecule with 6
carbon Carbon () is a chemical element with the chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—its atom making four electrons available to form covalent bond, covalent chemical bonds. It belongs to gro ...
atoms, 12
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the chemical ...
atoms and 6
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...
atoms). One of the most famous molecules,
water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
, is known almost universally by its chemical formula: H2O (meaning that it contains 2 hydrogen atoms and 1 oxygen atom.) A subscript is also used to distinguish between different versions of a
subatomic particle In physical sciences, a subatomic particle is a particle that composes an atom Every atom is composed of a atomic nucleus, nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of n ...
. Thus electron, muon, and tau
neutrino A neutrino ( ; denoted by the Greek letter Nu (letter), ) is a fermion (an elementary particle with spin-1/2, spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electric charge, electricall ...
s 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 ''x''0 and ''x''f might 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. Commonly, variables with a zero in the subscript are referred to as the variable name followed by " nought" (e.g. v0 would be read, "v-nought"). Subscripts are often used to refer to members of a mathematical
sequence In mathematics, a sequence is an enumerated collection of mathematical object, objects in which repetitions are allowed and order theory, order matters. Like a Set (mathematics), set, it contains Element (mathematics), members (also called ''eleme ...
or set or elements of a vector. For example, in the sequence ''O'' = (45, −2, 800), ''O''3 refers to the third member of sequence ''O'', which is 800. Also in mathematics and computing, a subscript can be used to represent the
radix In a positional numeral system, the radix or base is the number of unique numerical digit, digits, including the digit zero, used to represent numbers. For example, for the decimal/denary system (the most common system in use today) the radix (b ...
, or base, of a written number, especially where multiple bases are used alongside each other. For example, comparing values in
hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a Numeral system#Positional systems in detail, positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system ...
, denary, and
octal The octal numeral system, or oct for short, is the base-8 number system, and uses the digits 0 to 7. This is to say that 10octal represents eight and 100octal represents sixty-four. However, English, like most languages, uses a base-10 numbe ...
one might write Chex = 12dec = 14oct. Subscripted numbers dropped below the baseline are also used for the denominators of stacked
fraction A fraction (from la, fractus, "broken") represents a part of a whole or, more generally, any number of equal parts. When spoken in everyday English, a fraction describes how many parts of a certain size there are, for example, one-half, eight ...
s, like this: .


Subscripts that are aligned with the baseline

The only common use of these subscripts is for the denominators of diagonal fractions, like or the signs for
percent In mathematics, a percentage (from la, per centum, "by a hundred") is a number or ratio expressed as a fraction (mathematics), fraction of 100. It is often Denotation, denoted using the percent sign, "%", although the abbreviations "pct.", "p ...
%, permille ‰, and
basis point A basis point (often abbreviated as bp, often pronounced as "bip" or "beep") is one hundredth of 1 percentage point. The related term '' permyriad'' means one hundredth of 1 percent. Changes of interest rates are often stated in basis points. If ...
‱. Certain standard abbreviations are also composed as diagonal fractions, such as (care of), (account of), (addressed to the subject), or in Spanish (cada uno/una, "each one").


Superscripts that typically do not extend above the ascender line

These superscripts typically share a baseline with
numerator A fraction (from la, fractus, "broken") represents a part of a whole or, more generally, any number of equal parts. When spoken in everyday English, a fraction describes how many parts of a certain size there are, for example, one-half, eight ...
digits, the top of which are aligned with the top of the full-height numerals of the base font; lowercase ascenders may extend above. Ordinal indicators are sometimes written as superscripts (, , , , rather than 1st, 2nd, 3rd, 4th), although many English-language
style guide A style guide or manual of style is a set of standards for the writing, formatting, and design of documents. It is often called a style sheet, although that term also has multiple other meanings. The standards can be applied either for gene ...
s recommend against this use. Other languages use a similar convention, such as 1er or 2e in French, or 4ª and 4º in Galician and Italian, or 4.ª and 4.º in Portuguese and Spanish. In medieval manuscripts, many superscript as well as subscript signs were used to abbreviate text. From these developed modern
diacritical mark A diacritic (also diacritical mark, diacritical point, diacritical sign, or accent) is a glyph added to a letter (alphabet), letter or to a basic glyph. The term derives from the Ancient Greek (, "distinguishing"), from (, "to distinguish"). T ...
s (
glyph A glyph () is any kind of purposeful mark. In typography, a glyph is "the specific shape, design, or representation of a character". It is a particular graphical representation, in a particular typeface, of an element of written language. A g ...
s, or "accents" placed above or below the letter). Also, in early
Middle High German Middle High German (MHG; german: Mittelhochdeutsch (Mhd.)) is the term for the form of German language, German spoken in the High Middle Ages. It is conventionally dated between 1050 and 1350, developing from Old High German and into Early New Hi ...
, 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 vowels and consonants were used in this way, as in ſheͨzze and 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 A service mark or servicemark is a trademark used in the United States and several other countries to identify a Service (economics), service rather than a product (business), product. When a service mark is federally registered, the standard ...
() and
trademark A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign (semiotics), sign, design, or expression (language), expression that identifies Good (economics and accounting), product ...
(). The signs for
copyright A copyright is a type of intellectual property that gives its owner the exclusive right to copy, distribute, adapt, display, and perform a creative work, usually for a limited time. The creative work may be in a literary, artistic, education ...
© and
registered trademark The registered trademark symbol, , is a typographic symbol that provides notice that the preceding word or symbol is a trademark or service mark that has been registered with a national trademark office. A trademark is a symbol, word, or word ...
® are also sometimes superscripted, depending on the typeface or house style. On handwritten documents and signs, a monetary amount may be written with the cents value superscripted, as in $ or . Often the superscripted numbers are underlined: $, ⁵⁰. The
currency symbol A currency symbol or currency sign is a graphic symbol used to denote a currency unit. Usually it is defined by the monetary authority, like the national central bank for the currency concerned. In formatting, the symbol can use various format ...
itself may also be superscripted, as in . Diagonal fractions with subscripts that are aligned with the baseline also fall into this category.


Superscripts that typically extend above the ascender line

Both low and high superscripts can be used to indicate the presence of a
footnote A note is a string of text placed at the bottom of a page (paper), page in a book or document or at the end of a chapter, volume, or the whole text. The note can provide an author's comments on the main text or citations of a reference work in ...
in a document, like this5 or thisxi. 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 taste, but high-set footnotes tend to be more common, as they stand out more from the text. In
mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
, high superscripts are used for
exponentiation Exponentiation is a mathematics, mathematical operation (mathematics), operation, written as , involving two numbers, the ''Base (exponentiation), base'' and the ''exponent'' or ''power'' , and pronounced as " (raised) to the (power of) ". W ...
to indicate that one number or variable is raised to the power of another number or variable. Thus ''y''4 is ''y'' raised to the fourth power, 2''x'' is 2 raised to the power of ''x'', and the famous equation includes a term for the
speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special relativity, special theory of relativity, is ...
squared. This led over time to an "
abuse of notation In mathematics, abuse of notation occurs when an author uses a mathematical notation in a way that is not entirely formally correct, but which might help simplify the exposition or suggest the correct Mathematical intuition, intuition (while possi ...
" whereby superscripts indicate iterative
function composition In mathematics, function composition is an operation that takes two function (mathematics), functions and , and produces a function such that . In this operation, the function is function application, applied to the result of applying the ...
, including
derivative In mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented ...
s. In an unrelated use, superscripts also indicate contravariant tensors in
Ricci calculus In mathematics, Ricci calculus constitutes the rules of index notation and manipulation for tensors and tensor fields on a differentiable manifold, with or without a metric tensor or Connection (mathematics), connection. It is also the modern nam ...
. The charges of ions and
subatomic particle In physical sciences, a subatomic particle is a particle that composes an atom Every atom is composed of a atomic nucleus, nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of n ...
s are also denoted by superscripts. is a negatively charged
chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
atom, is an atom of
lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...
with a positive charge of four, is an
electron The electron ( or ) is a subatomic particle with a negative one elementary charge, elementary electric charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are generally thought t ...
, is a
positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 ''elementary charge, e'', a spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest ...
, and is an
antimuon A muon ( ; from the Greek alphabet, Greek letter mu (letter), mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 ''elementary charge, e'' and a spin-½, spin of , but with a m ...
. Atomic
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbe ...
s are written using superscripts. In symbolic form, the number of
nucleon In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number, mass number (nucleon number). Until the 1960s, n ...
s is denoted as a superscripted prefix to the
chemical symbol Chemical symbols are the abbreviations used in chemistry for chemical elements, functional groups and chemical compounds. Element symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with th ...
(for example , , , , and ). The letters ''m'' or ''f'' may follow the number to indicate metastable or fission
isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. Isomerism is existence or possibil ...
s, as in or . Subscripts and superscripts can also be used together to give more specific information about
nuclide A nuclide (or nucleide, from atomic nucleus, nucleus, also known as nuclear species) is a class of atoms characterized by their number of protons, ''Z'', their number of neutrons, ''N'', and their nuclear energy state. The word ''nuclide'' was co ...
s. For example, denotes an atom of
uranium Uranium is a chemical element with the Symbol (chemistry), symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. ...
with 235 nucleons, 92 of which are
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s. A chemical symbol can be completely surrounded: is a divalent cation of
carbon Carbon () is a chemical element with the chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—its atom making four electrons available to form covalent bond, covalent chemical bonds. It belongs to gro ...
with 14 nucleons, of which six are protons and 8 are
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the atomic nucleus, nuclei of atoms. Since protons and ...
s, and there are two atoms in this chemical compound. The numerators of stacked fractions (such as ) 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. Another minor adjustment that is often omitted by renderers is the control of the direction of movement for superscripts and subscripts, when they do not lie on the baseline. Ideally this should allow for the font, e.g. italics are slanting; most renderers adjust the position only vertically and do not also shift it horizontally. This may create a collision with surrounding letters in the same italic font size. One can see an example of such collision on the right side when rendered in HTML (see the figure on the right). To avoid this, it is often desirable to insert a small positive horizontal margin (or a thin space) (on the left side of the first superscript character), or a negative margin (or a tiny backspace) before a subscript. It is more critical with glyphs from fonts in Oblique styles that are more slanted than those from fonts in Italic style, and some fonts reverse the direction of slanting, so there is no general solution except when the renderer takes into account the font metrics properties that specifies the angle of slanting, However the same problem occurs more generally between spans of normal glyphs (non-superscript and non-subscript) when slanting styles are mixed.


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 downrather than separately designed subscript or superscript glyphs. Professional typesetting programs such as
QuarkXPress QuarkXPress is a desktop publishing Desktop publishing (DTP) is the creation of documents using page layout software on a personal ("desktop") personal computer, computer. It was first used almost exclusively for print publications, but now it ...
or
Adobe InDesign Adobe InDesign is a desktop publishing and page layout designing software application software, application produced by Adobe Inc. and first released in 1999. It can be used to create works such as posters, flyers, brochures, magazines, newspap ...
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).


HTML

In
HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScript ...
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 MediaWiki is a Free and open-source software, free and open-source wiki software. It is used on Wikipedia and almost all other Wikimedia movement, Wikimedia Website, websites, including Wiktionary, Wikimedia Commons and Wikidata; these sit ...
), subscripts are typeset with the
underscore An underscore, ; also called an underline, low line, or low dash; is a line drawn under a segment of text. In proofreading, underscoring is a convention that says "set this text in italic type", traditionally used on Manuscript (publishing), man ...
, while superscripts are made with the caret. Thus $X_$ produces X_, and $X^$ produces X^. In LaTeX text mode the math method above is inappropriate, as letters will be in math italic, so the command n\textsuperscript will give nth and A\textsubscript will give Abase (textual ''sub''scripts are rare, so \textsubscript is not built-in, but requires the ''fixltx2e'' package). As in other systems, when using UTF-8 encoding, the masculine º and feminine ª ordinal indicators can be used as characters, with no need to use a command. In line with its origin as a superscript circle, the
degree symbol The degree symbol or degree sign, , is a typography, typographical symbol that is used, among other things, to represent Degree (angle), degrees of arc (e.g. in geographic coordinate systems), hours (in the medical field), degree (temperature), d ...
(°) is composed by a superscript circle operator (∘). ^. Superscripts and subscripts of arbitrary height can be done with the \raisebox command: the first argument is the amount to raise, and the second is the text; a negative first argument will lower the text. In this case the text is not resized automatically, so a sizing command can be included, e.g. go\raisebox.


Unicode

Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, ...
defines subscript and superscript characters in several areas; in particular, it has a full set of superscript and subscript digits. Owing to the popularity of using these characters to make fractions, most modern fonts render most or all of these as cap height superscripts and baseline subscripts. The same font may align letters and numbers in different ways. Other than numbers, the set of super- and subscript letters and other symbols is incomplete and somewhat random, and many fonts do not contain them. Because of these inconsistencies, these glyphs may not be suitable for some purposes (see ''Uses'', above).


OpenType

Several advanced features of
OpenType OpenType is a format for scalable computer fonts. It was built on its predecessor TrueType, retaining TrueType's basic structure and adding many intricate data structures for prescribing typography, typographic behavior. OpenType is a registered ...
typefaces are supported 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. They can be available via activating subs or sups feature tag. These feature tags can be turned on if software environment support optional features. In addition, some other typefaces placed them in a Unicode
Private Use Area In Unicode, a Private Use Area (PUA) is a range of code points that, by definition, will not be assigned characters by the Unicode Consortium. Three private use areas are defined: one in the Plane (Unicode)#Basic Multilingual Plane, Basic Multili ...
.


See also

*
Mathematical notation Mathematical notation consists of using glossary of mathematical symbols, symbols for representing operation (mathematics), operations, unspecified numbers, relation (mathematics), relations and any other mathematical objects, and assembling the ...
*
Typographical conventions in mathematical formulae Typographical conventions in mathematical formulae provide uniformity across mathematics, mathematical texts and help the readers of those texts to grasp new concepts quickly. Mathematical notation includes letters from various alphabets, as well ...
* Superior letter *
Furigana is a Japanese language, Japanese reading aid consisting of smaller kana or syllabic characters printed either above or next to kanji (Logogram, logographic characters) or other characters to indicate their pronunciation. It is one type of ruby ...
*
Ruby character Ruby characters or rubi characters () are small, annotative gloss (annotation), glosses that are usually placed above or to the right of logogram, logographic characters of languages in the East Asian cultural sphere, such as Sinitic languages, Ch ...
*
Typesetting Typesetting is the composition of Written language, text by means of arranging metal type, physical ''type'' (or ''sort'') in mechanical systems or ''glyphs'' in digital systems representing ''character (symbol), characters'' (letters and ot ...
*
Font In movable type, metal typesetting, a font is a particular #Characteristics, size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "Sort (typesetting), sort") for each glyph. A typeface consists of a range of ...
* Superscripts and Subscripts (Unicode block)


References


Bibliography

* Bringhurst, Robert (2005), '' The Elements of Typographic Style'', 3rd ed., Vancouver: Hartley and Marks, .


External links


Vincent Connare's type-design standards for Microsoft

Vertical alignment questions
from Typophile {{DEFAULTSORT:Subscript And Superscript Typography