Punctuation Marks and Their Uses

Table of Contents

1. Period (.)

• Historical Context: The period has been used since ancient Greek and Latin texts to mark the end of a sentence. In medieval manuscripts, it was often accompanied by a space or a pilcrow (¶) to indicate a new paragraph.
• Used at the end of a sentence.
• Used after some abbreviations (e.g., Dr., Mr., etc.).
• Used for ordinal numbers (e.g., 1. 2. 3.).
• Used after letters and numbers in lists (e.g., a., b., c., I., II., IV.).
• Used in dates to separate day, month, and year (e.g., 12.10.2023).
• If dates are written in word form, no dots are used (e.g., 12 October 2023).
• Used in time notation (e.g., 09.15).
• Used as a multiplication symbol (e.g., 5.2 = 10).
• Used at the end of a biography.
• Used to make reading long numbers easier in groups of three (e.g., 42.632.642.243).
• Used as a decimal separator (e.g., 3.14159265).
• Used to show which part of a text corresponds to a page number in a table of contents (e.g., "Introduction...............5").
• Used to align text when whitespace cannot be used (e.g., in formatted tables or lists).
• Used for empty spaces in quizzes or fill-in-the-blank exercises (e.g., "The capital of France is ........").
• In object-oriented languages to access properties or methods (e.g., object.method()).
• In regular expressions, matches any single character (e.g., "a.c" matches "abc", "aac", "a c").
• In file systems, separates filenames from extensions (e.g., "document.pdf").
• In domain names, separates subdomains and top-level domains (e.g., "example.com").
• In chess notation, indicates a move without commentary (e.g., "1.e4 e5 2.Nf3").
• In music, indicates staccato when placed above/below a note (e.g., ♩. = short detached note).
• In chemical formulas, separates water molecules in hydrates (e.g., CuSO₄·5H₂O).
• In Braille, forms the basis for numerous characters by its placement in the 6-dot cell.
• In Morse code, represents the letter "E" as a single dot.
• In some languages (German, Russian), used in abbreviations without spaces (e.g., "z.B." for "zum Beispiel").
• In Japanese, marks the end of sentences (。), though the symbol differs from Western period.
• In some programming languages, indicates floating-point numbers (e.g., 3. vs 3).
• In version numbers, separates major, minor and patch versions (e.g., 2.5.1).
• In linguistics, marks syllable boundaries in phonetic transcription (e.g., [ˈæ.pl̩]).
• In some shorthand systems, represents common word endings or prefixes.
• In astronomy, precedes the genitive form of constellation names (e.g., "Alpha Centauri" abbreviated as "α Cen.").
• In some numbering systems, separates chapter and verse numbers (e.g., "John 3.16").
• In mathematical notation, indicates a derivative with respect to time (ẋ = dx/dt).
• In some writing systems, marks abbreviation or contraction (e.g., medieval manuscripts).
• In some calendar systems, separates era designations (e.g., "A.D. 2023").
• In some ancient numbering systems, functioned as a zero placeholder.
• In some graphical user interfaces, indicates hidden files when prefixed (e.g., ".bashrc").
• In some markup languages, indicates special processing instructions.
• In some medieval texts, indicated the end of a thought rather than a grammatical sentence.

2. Exclamation Mark (!)

• Historical Context: The exclamation mark originated from the Latin word "io," meaning "joy," which was written vertically and eventually evolved into the modern "!".
• In Spanish, an inverted exclamation mark (¡) is used at the beginning of an exclamatory sentence (e.g., ¡Hola!). In French, a space is often added before the exclamation mark (e.g., "Bonjour !").
• Used at the end of a sentence to show excitement, anger, or pain.
• Used in addressing or warning someone.
• In chess, it indicates a good or great move.
• In programming, it indicates a negation.
• No space before the exclamation mark, but a space and capital letter after it.
• In mathematics the exclamation mark represents the factorial (5! = 5 * 4 * 3 * 2 * 1)
• In mathematics the exclamation mark before the number represents the subfactorial/derangement (!n = n*(n-1)!+(-1)^n)
• In chess '!' denotes a good or great move
• Logical NOT operator (!true == false)
• Negation in many languages (!= for "not equal")
• In Ruby, denotes destructive methods (e.g., sort vs sort!)
• In formal logic, represents the uniqueness quantifier (∃!x).
• In geometry, sometimes marks right angles (90°!)
• In informal writing, multiple exclamation marks ("!!!") show extreme emphasis (though considered poor style in formal writing).
• In some languages (Arabic, Hebrew), appears as mirrored (״) due to right-to-left writing.
• In chemical nomenclature, indicates radical species when after atomic symbols (e.g., Cl!).
• In linguistics, marks clicks in phonetic transcription (e.g., !Kung language).
• In weather maps, sometimes indicates unusual or extreme weather phenomena.
• In musical notation, can appear above notes as an articulation mark (marcato).
• In proofreading, sometimes used in margins to draw attention to important text.
• In regular expressions, has special meaning in certain positions (e.g., negative lookahead).
• In chess problem notation, indicates a key move in the solution.
• In some programming languages, denotes type conversion (e.g., !! in JavaScript for boolean conversion).
• In certain markup languages, indicates special processing instructions.
• In some medieval manuscripts, appeared as a punctus exclamativus before standardization.
• In some board games, marks special actions or events on game cards.
• In certain scripting languages, indicates variable substitution.
• In some word processors, triggers autocorrection or smart punctuation features.
• In certain file formats, appears in magic numbers identifying file types.
• In some command-line interfaces, represents event designators (e.g., !!)
• In certain programming languages, denotes macros or special operators.
• In some chat systems, precedes commands (!help, !join).
• In certain games, indicates special abilities or power-ups.
• In some puzzle notations, marks particularly challenging steps.
• In certain documentation systems, indicates warnings or important notes.

3. Comma (,)

• Historical Context: The comma was introduced by the Greek scholar Aristophanes of Byzantium in the 3rd century BCE as a way to indicate a short pause in speech.
• Used between word groups of the same kind (e.g., apples, oranges, and bananas).
• No space before the comma, but a space after it. No capital letter after the comma.
• Used to divide sequential sentences.
• Used to emphasize a noun that is far from other elements.
• Used in insentence tellings and insistence sentences.
• Used to empower the meaning of repeated words (e.g., "No, no, no!").
• Used as a replacement for quotation marks in some cases.
• Used after acceptance or rejection (e.g., "No, I'd rather not.").
• Used to show disconnection in a sentence.
• Used after addressing someone (e.g., "John, can you help me?").
• Used to make reading long numbers easier in groups of three (e.g., 42,632,642,243).
• Used as a decimal separator in some regions (e.g., 3,14159265).
• Used after the writer's name in bibliographies.
• Used in the surname-first format (e.g., Smith, John).
• Used in music notation to indicate breathing points.
• In programming, the comma is used to separate elements in arrays or parameters in functions (e.g., [1, 2, 3] or function(a, b, c)).
• In music, indicates breath marks or slight pauses.
• In bibliographies, separates author names from titles.
• In inverted name formats (e.g., "Smith, John").
• In some languages (German), used as quotation marks („Guten Tag").
• In chemical formulas, separates ligands.
• In chess notation, separates move numbers from moves (1. e4, e5).
• In regular expressions, has special meaning in certain contexts.
• In some file formats (CSV), serves as field delimiter.
• In linguistics, separates phonetic transcriptions.
• In some shorthand systems, represents common word fragments.

4. Semicolon (;)

• Historical Context: The semicolon was introduced by the Italian printer Aldus Manutius in the 15th century as a way to separate clauses that are more closely related than those separated by a period.
• Used to divide sentences that are already divided by commas.
• Used to divide sequential similar words that are already divided by commas.
• Used in mathematics to show disambiguation in parameters (e.g., Jacobi theta functions: sn(u;m), sn(u;k), sn(u|t)).
• In some notations, separates matrix rows
• In differential equations, separates variables
• In programming, the semicolon is often used to terminate statements (e.g., in C++, Java, or JavaScript).
• Separates clauses in for loops (for(i=0; i<10; i++))
• In some languages, separates array dimensions (array[1;2])
• In CSS, separates property-value pairs
• In Greek, functions as a question mark.
• In some citation styles, separates multiple citations.
• In some file formats, serves as comment indicator.
• In chess notation, separates alternative move sequences.
• In some shorthand systems, represents common word endings.
• In some ancient texts, marked intermediate pauses.

5. Colon (:)

• Historical Context: The colon was used in ancient Greek texts to indicate a pause longer than a comma but shorter than a period. It was also used in medieval manuscripts to introduce lists or quotations.
• In Swedish, the colon is used after greetings in formal letters (e.g., "Kära Anna:"). In Finnish, the colon is used to indicate a long vowel in phonetic transcriptions (e.g., "a:").
• Used to divide sentences that are already divided by semicolons.
• Used to divide sequential similar words that are already divided by semicolons.
• Used before giving examples (e.g., "There are three colors: red, blue, and green.").
• Used to introduce explanations or elaborations (e.g., "The reason is simple: practice").
• Used to introduce quotations (e.g., "He said: 'I'll be there'").
• Used between independent clauses when the second explains the first (e.g., "Life is short: enjoy it").
• Used in time notation (e.g., 10:30 PM).
• Used in ratios and proportions (e.g., 2:1 ratio).
• Used in biblical citations (e.g., John 3:16).
• Used before explanations or elaborations.
• Used before quotations.
• In linguistics, used to show elongation.
• In literature, used before a speech and after the speaker.
• Used in web addresses (e.g., https://example.com).
• Used as a division symbol in mathematics.
• Used as a space in some languages which dont have space (𐱅𐰀𐰭𐰼𐰃:𐰖𐰀𐰺𐱃𐰢𐰃𐱁).
• In some languages (Swedish, Finnish), used after salutations.
• In linguistics, marks vowel length or tone.
• In chess notation, indicates captures (Nxe4).
• In some file systems, separates drive names (C:).
• In some ancient scripts, functioned as word separator.
• In some shorthand systems, represents common prefixes/suffixes.
• In set notation, means "such that" ({x : x > 0})
• In some notations, separates function from domain (f: X→Y)
• In programming, the colon is used in ternary operators (e.g., condition ? true : false) and to define key-value pairs in dictionaries (e.g., {"key": "value"}).

6. Ellipsis (...)

• Historical Context: The ellipsis was first used in the 16th century to indicate omitted text in quotations. It became more common in the 18th century with the rise of the novel.
• Used after unfinished sentences.
• Used to censor words considered rude.
• Used in citations and quotations to indicate omitted text.
• Used in literature to show someone cutting off another's speech.
• Used to show waiting or hesitation.
• Used after ? and ! to reinforce meaning (e.g., "What...?" or "No way...!").
• Used in dialogues to indicate no answer.
• The ellipsis is often used to indicate a pause or hesitation in dialogue
• Only three dots are standard; more than three are not correct, even if used to express longer pauses.
• In programming, the ellipsis is used in variadic functions to indicate a variable number of arguments (e.g., in C: printf("%d...", 1, 2, 3)).

7. Question Mark (?)

• Historical Context: The question mark originated from the Latin word "quaestio," meaning "question," which was abbreviated as "qo" and eventually evolved into the modern "?".
• In Spanish, an inverted question mark (¿) is used at the beginning of a question (e.g., ¿Cómo estás?). In Greek, the question mark is represented by a semicolon (;).
• Used at the end of a question.
• Used after a sentence with a question word but not a direct question (e.g., "I wonder why?").
• Used after unknown, ambiguous, or questionable dates, places, or numbers.
• In sequential sentences, the question mark is placed at the very end.
• Used in chess to indicate a mistake.
• Used in mathematics to represent Minkowski's question-mark function, a function with fractal properties.
• Used in ternary operators, optional chaining, and nullish coalescing in programming.
• In regular expressions to indicate optional elements (e.g., "colou?r" matches both "color" and "colour").

8. Parenthesized Question Mark ( (?) )

• Used to express subtle doubt.
• Used to indicate an unclear or questionable statement.
• In chess, it indicates an inaccuracy or an uncommented inferior move.

9. Parenthesized Exclamation Mark ( (!) )

• Used to express subtle exclamation.
• Used after mockery, ridicule, or sarcasm.
• Used to indicate unclear excitement.
• In chess, it indicates an uncommented good move.

10. Short Line (-)

• Used to divide words that don't fit on the page (e.g., at the end of a line).
• Used to divide in-sentence quotes and in-sentence sentences.
• In linguistics, used to divide the root of a word (e.g., "re-construct").
• Used before extensions suffixes and prefixes (e.g., -ing, -ed, -s).
• Used to divide phonemes and syllables (e.g., syl-la-ble).
• Used in "from-to" constructions (e.g., French-Turkish dictionary).
• Used as a subtraction symbol in mathematics (e.g., 5 - 3 = 2).
• Sometimes used in compound words or to join parts of a word (e.g., mother-in-law).

14. Long Line (—)

• Used in dialogues without the speaker's name (e.g., "—Where are you going?").
• Used in theatre plays after the speaker's name (e.g., "John — I can't believe you did that!").

11. Hyphen (-)

• Historical Context: The hyphen has been used since the Middle Ages to join words or syllables. It became more standardized with the advent of printing in the 15th century.
• Used to join words or parts of words (e.g., well-known, co-operate).
• Used in compound adjectives before a noun (e.g., a high-quality product).
• Used to avoid ambiguity (e.g., re-cover vs. recover).
• Used in numbers (e.g., twenty-one, forty-two).
• Used in prefixes (e.g., ex-president, self-aware).
• In programming, the hyphen is used in variable names (e.g., "user-name") and in CSS for property names (e.g., "background-color").

12. En Dash (–)

• Historical Context: The en dash was introduced in the 18th century to indicate ranges or connections between words. It is named after the width of the letter "n."
• Used to indicate a range (e.g., 1990–2000, pages 10–20).
• The en dash is used for ranges (e.g., "pages 10–20"). In American English, it is often replaced by a hyphen.
• Used to show connections or relationships (e.g., London–Paris flight).
• Used in place of "to" or "through" (e.g., Monday–Friday).
• In mathematics, the en dash is used to indicate subtraction (e.g., 5 – 3 = 2).

13. Em Dash (—)

• Historical Context: The em dash was introduced in the 18th century to indicate a break or pause in a sentence. It is named after the width of the letter "m."
• Used to indicate a break or pause in a sentence (e.g., "I was going to tell you—but never mind.").
• Used to set off parenthetical information (e.g., "The book—which was published last year—is already a bestseller.").
• he em dash is used to set off parenthetical information (e.g., "The book—which was published last year—is already a bestseller.").
• Used to emphasize a point (e.g., "She was the one—the only one—who could solve the problem.").
• Used to replace commas, colons, or parentheses for stronger emphasis.
• In informal writing, the em dash is used to indicate an abrupt change in thought (e.g., "I was going to tell you—but never mind.").

15. Slash (/)

• Historical Context: The slash has been used since the Middle Ages to indicate alternatives or fractions. It became more common with the advent of typewriters in the 19th century.
• Used between things of the same kind (e.g., apple/banana/pear, punctuation symbols/marks).
• Used between lines of a poem if line breaks are not applicable.
• Used in addresses between apartment number and door number, and between city and district (e.g., 123/4, Istanbul/Beyoğlu).
• Used as a variation of extension prefixes or suffixes (e.g., -s/-es, -d/-ed).
• Used in web addresses (e.g., https://tesertcode.github.io/DC.html).
• Used as a division symbol in mathematics (e.g., 10/2 = 5).
• Used in dates (e.g., 17/08/1534).

15.5. Backslash (\)

• Historical Context: The backslash was introduced in the 20th century with the advent of computers. It was originally used to indicate escape sequences in programming languages.
• In programming, the backslash is used to escape special characters (e.g., "\n" for a newline). In file paths, it is used to separate directories (e.g., "C:\Users\Name").
• In mathematics, the backslash is used to denote set difference (e.g., A \ B).

16. Double Quote (")

• Historical Context: Quotation marks were first used in the 16th century to indicate direct speech or quotations. They were originally called "inverted commas."
• In British English, single quotation marks are often used (e.g., 'quote'), while in American English, double quotation marks are standard (e.g., "quote"). In French, guillemets (« ») are used (e.g., «Bonjour»).
• Used in citations (e.g., "According to Einstein...").
• Used in quotations (e.g., She said, "Hello!").
• Used to emphasize a word or phrase (e.g., This is "important").
• Used for satiric effect (e.g., He is so "talented").
• Used for in-sentence sentences (e.g., The term "punctuation" refers to...).
• Used for strings in programming (e.g., "Hello, World!").

17. Single Quote (`)

• Used when quotes within quotes are required (e.g., She said, "He told me, 'I'll be there.'").
• Used for characters in programming (e.g., `a`, `1`).

17.5. Asterisk (*)

• Historical Context: The asterisk has been used since ancient times to indicate footnotes or omissions. It became more common with the advent of printing in the 15th century.
• In linguistics, the asterisk is used to indicate reconstructed or hypothetical forms (e.g., *proto-word). In programming, it is used for multiplication (e.g., 5 * 3 = 15) and as a wildcard character (e.g., "*.txt").
• In mathematics, the asterisk is used to denote convolution (e.g., f * g).

18. Denden ('')

• Used for repeating words that are under each other (e.g., filleth me with thine soul / '' '' '' '' sin).

19. Apostrophe (')

• Historical Context: The apostrophe was first used in the 16th century to indicate omitted letters (e.g., "don't" for "do not"). It later evolved to indicate possession (e.g., "John's book").
• Used after special names with suffixes (e.g., O'Connor).
• Used after people's names (e.g., John's book).
• Used after abbreviations (e.g., gov't for government).
• Used after numbers (e.g., the '90s).
• Used to indicate silent letters (e.g., rock 'n' roll).
• Used after single-letter words or characters that take suffixes (e.g., a's, I'm).

19.5. Ampersand (&)

• Historical Context: The ampersand originated from the Latin word "et," meaning "and." It was commonly used in medieval manuscripts and became a standard character in typefaces.
• In English, the ampersand is frequently used in company names to denote partnerships (e.g., "Johnson & Johnson" and "Barnes & Noble").
• In programming, it has various applications, including logical AND operations (e.g., if (a && b)), bitwise operations (e.g., a & b), and referencing memory addresses in languages like C and C++ (e.g., &variable).
• In typography, the ampersand is often stylized in different fonts to enhance the aesthetic of a logo or brand identity.
• In shorthand writing, the ampersand is used to save space and increase efficiency in note-taking.
• In early English alphabet recitations, children would say "and per se and" when reciting the symbol at the end of the alphabet, which eventually evolved into the modern word "ampersand."
• In some formal and artistic writings, the ampersand is used in place of "and" to add a touch of elegance or uniqueness to a title or phrase.
• In mathematics it can denote "array of" (5&3 = {3,3,3,3,3}).

19.75. At Symbol (@)

• Historical Context: The at symbol was originally used in commerce to indicate "at the rate of" (e.g., "10 apples @ $1"). It gained widespread use with the advent of email in the 20th century.
• In email addresses, the at symbol is used to separate the user’s name from the domain (e.g., user@example.com).
• In social media, the symbol is used to tag or mention users (e.g., "@username" on Twitter and Instagram).
• In programming, the at symbol is used in various contexts, such as decorators in Python (@decorator) and attribute annotations in Java and C#.
• In some languages like Spanish and Portuguese, "arroba" (the word for @) was historically used as a unit of weight.
• In certain contexts, the symbol is used in business and accounting documents to denote "at the rate of" or "per unit."
• Some artistic and typographic designs incorporate the at symbol in creative ways, often stylizing it uniquely for branding.
• In sports and event scheduling, the at symbol is used to indicate location (e.g., "Team A @ Team B").
• In mathematics it can denote the index (phi(1@3) = phi(1,0,0,0)).

19.875. Hash/Pound Symbol (#)

• Historical Context: The hash symbol originated from the Latin abbreviation "lb" for "pound weight." It evolved into the modern "#" symbol and was used in telephony and computing.
• In British English, the symbol is called the "hash," while in American English, it is often referred to as the "pound sign."
• In social media, the hash symbol is widely used to create hashtags, which help categorize content and make topics searchable (e.g., #ThrowbackThursday).
• In programming, the symbol is used to denote comments (e.g., # This is a comment in Python) and in some languages like C for preprocessor directives (e.g., #include).
• In programming, the symbol is used to denote hexadecimal values (#FF0000 = red).
• In musical notation, the hash symbol represents a sharp note, altering a pitch by a half-step (e.g., F#).
• In telephony, the symbol is used for special functions, such as in automated phone menus where users press # to confirm an action.
• In chess notation, the hash symbol represents checkmate (e.g., Qh5# means the queen delivers checkmate on h5).

19.9375. Tilde (~)

• Historical Context: The tilde originated from the Latin word "titulus," meaning "title" or "superscription." It was used in medieval manuscripts to indicate abbreviations.
• In Spanish, the tilde is used to indicate nasalization, as in "mañana."
• In Portuguese, the tilde is used to mark nasal vowels (e.g., "não").
• In mathematics, the tilde is often used to denote approximation (e.g., x ~ y means x is approximately equal to y).
• In Unix-based operating systems, the tilde represents a user’s home directory (e.g., cd ~/Documents).
• In logic and programming, the tilde is used as a bitwise NOT operator (e.g., ~5 in C and JavaScript).
• In URLs and file paths, the tilde is sometimes used as an alias for a specific directory, especially in web hosting.

19.96875. Caret (^)

• Historical Context: The caret originated from the Latin word "caret," meaning "it is lacking." It was used in proofreading to indicate where text should be inserted.
• In mathematics, the caret is commonly used for exponentiation (e.g., x^y).
• In mathematics, the multiple carets is commonly used for hyperoperators (x^^y for tetration x^^^y for pentation etc.).
• In programming, the caret is used in regular expressions to denote the start of a line (e.g., ^start means "start of string").
• In LaTeX and other markup languages, the caret is used to create superscripts (e.g., x^{2} for x²).
• In command-line interfaces, the caret is sometimes used as an escape character (e.g., Windows Command Prompt).
• In some texting and internet slang, two carets are used to represent raised eyebrows or emphasis (e.g., ^^ meaning excitement or agreement).

19.984375. Pipe (|)

• Historical Context: The pipe symbol originated from the vertical bar used in medieval manuscripts to indicate a pause or break. It became more common with the advent of typewriters.
• Programming:
  • Logical OR operations (e.g., if (a || b))
  • Command output redirection in Unix/Linux (e.g., ls | grep file)
  • Backus-Naur form notation (< syntax > ::= < rule > | < rule > << yntax >)
  • List comprehensions ([x*2 | x < - [1..10], even x])
  • Concurrency operator (process1 | process2)(in occam)
  • Pi Calculus Free names (P|Q All free names of P and Q)
  • APL language operations (residue/modulo operation in APL)
  • Pattern matching: (case x of 1 | 3 | 5 -> "Odd", 2 | 4 | 6 -> "Even")
  • Text markup delimiter
  • Pipeline operator: data |> filter |> map |> reduce (JavaScript/Elixir)
  • String concatenation
  • SQL UNION: SELECT a FROM table1 UNION SELECT b FROM table2
• Mathematics:
  • Absolute value notation (e.g., |x|)
  • Set notation (e.g., {x | x > 0})
  • Cardinality in set theory
  • Determinant of a matrix
  • Order of groups in group theory
  • "Divides" relation (a|b)
  • Hypergeometric function parameters (e.g., H^m,n_p,q[z|(a1,A1)...])
  • Function restriction (f|A)
  • Function evaluation (f|_{a=2} = f(2))
  • Function difference (f|_{a}^{b} = f(b)-f(a))
  • Sheffer stroke (a|b is a NAND b)
  • Non-standard existential quantifier (∃x|φ(x))
  • Separation variables in elliptic integrals F(φ|m) = ∫₀^φ (1 - m sin²θ)^-½dθ (where the pipe separates the amplitude φ from the parameter m=k^2=eccentricity^2=elliptic-modulus^2)
• Physics & Chemistry:
  • Bra-ket notation in quantum mechanics |ψ⟩ (quantum state vector), ⟨φ| (dual vector), ⟨φ|ψ⟩ (inner product)
  • Supergroup notation G|H (denoting supergroup G with even subgroup H)
  • Cell notation (e.g., Zn | Zn2+ || Cu2+ | Cu)
• Other Sciences:
  • Conditional probability (P(A|B))
  • Shortest distance notation (A|d)
  • Propositional truncation in homotopy type theory (|a|:||A||)
• Linguistics & Phonetics:
  • Dental click representation (|ǀ (Unicode U+01C0) as in the word "|xam" (Khoisan language))
• Literature & Music:
  • Caesura marker (Devanagari danda) ( "To be | or not to be" (indicating pause in poetry))
  • Stanza separation when other symbols unavailable (The roses bloomed | The river flowed | Birds sang their tune)
  • Music section notation (|: A / / / :|)
• Games: Separation of different hands or scores in card games

19.99.Double Stroke (||)

• Parallel lines notation (AB||DC)
• Norm of a vector/matrix ||v|| = (v₁² + v₂² + ... + vₙ²)
• Propositional truncation in homotopy type theory
• Devanagari double danda "कः सः ||" (marks end of verse in Sanskrit texts)
• Alveolar lateral click in phonetics ||! (IPA notation for the lateral click sound)
• Cell notation separator in chemistry Zn || Zn²⁺ | Cu²⁺ | Cu (double pipe separates half-cells)
• Music repetition notation Repetition notation (||: A / / / :||)

19.9999. Solid Vertical Bar versus Broken Bar (¦)

Many early video terminals and dot-matrix printers rendered the vertical bar character as the allograph broken bar ¦. This distinction was made for several reasons:

• To distinguish from lowercase 'L' and uppercase 'I' on low-resolution devices
• To make vertical lines look more like horizontal dashed lines
• Briefly included in ASCII standard as a distinct character

Keyboard Implementation: Many keyboards display the broken bar on a keycap even though they produce a solid vertical bar, a legacy from 1980s-1990s IBM PC compatible computers.

Unicode: The broken bar is preserved as U+00A6 BROKEN BAR (sometimes called "parted rule").

Usage Notes: The broken bar is not an acceptable substitute for the vertical bar in mathematics, physics, or general typography. In some dictionaries, it marks stress that may be either primary or secondary.

20. Parentheses ( )

• Historical Context: Parentheses were first used in the 16th century to insert explanatory or qualifying material into a sentence. They were originally called "round brackets."
• Used for in-sentence sentences that are unrelated to the current sentence (e.g., "He finally answered (after taking five minutes to think).").
• In theatre plays, used to show movement or stage directions (e.g., "(walks to the door)").
• Used to show the poet or writer (e.g., "(Shakespeare)").
• In citations, triple dots can be parenthesized (e.g., "(...)").
• Exclamation points and question marks can be parenthesized for subtlety (e.g., "(?)" or "(!)").
• Used after matters (e.g., I), II), 1), 2), a), b)).
• Used for functions in mathematics (e.g., sin(x)).
• Used in taxonomy for subgenus, subspecies, and subgen (e.g., "Felis (catus)").
• Used to show structure in chemistry (e.g., "(CH₃)₂CO").
• Used for ranges in mathematics (e.g., "(4,7)" means four to seven).
• Used for combinations in mathematics (e.g., "(n, k)").
• In mathematics, parentheses are used to indicate the order of operations (e.g., (2 + 3) * 4).

21. Square Brackets [ ]

• Historical Context: Square brackets were introduced in the 17th century to indicate editorial additions or modifications to quoted text.
• Used for sounds (e.g., "[laughter]").
• When brackets inside brackets are required, square brackets are the more bordered ones (e.g., "[()]").
• Used for nested brackets in mathematics (e.g., "[(x + y) + z]").
• In bibliographies, used for extra details (e.g., "[2nd ed.]").
• Used for indexing in programming (e.g., "array[0]").
• Used for lists in programming (e.g., "[1, 2, 3]").
• Used for annotations (e.g., "[sic]").
• Used for modified citations (e.g., "[emphasis added]").
• Square-bracketed ellipsis is used for omitted material (e.g., "[...]").
• Used for closed ranges in mathematics (e.g., "[4,5]").
• Reversed square brackets are used for unclosed ranges in mathematics (e.g., "]3,4[").
• In proofreading, used for moving text (e.g., "[move to next paragraph]").
• In mathematics, used for version bracket notation (e.g., "[x]").
• Used for ions in chemistry (e.g., "[Na⁺]").
• In linguistics, square brackets are used to denote phonetic transcriptions (e.g., [ˈæpl̩] for "apple").

22. Curly Brackets { }

• Historical Context: Curly brackets were first used in the 16th century to group related items or to indicate a set of options.
• In music, they are known as "accolades" or "braces" and connect two or more lines (staves) of music that are played simultaneously.
• Used for super and subscripted numbers (e.g., "{n}").
• Used in chemistry to show further structure (e.g., "{CH₃}").
• Used for sets in mathematics (e.g., "{1, 2, 3}").
• In programming, they can mean an expression (e.g., "{x: x > 0}").
• In syntax diagrams, they are used for repetition (e.g., "{A, B}").
• In mathematics, used for Schläfli symbols (e.g., "{5,3}" for the regular dodecahedron).
• In mathematics, used for Stirling numbers of the second kind (e.g., "{n, k}").

23. Chevrons/Angle Brackets ⟨ ⟩

• Historical Context: Angle brackets were first used in the 18th century to denote mathematical expressions or to enclose quotations in some languages.
• In textual criticism, used in editions of pre-modern works.
• In comic books, used to mark dialogue translated notionally from another language.
• In linguistics, used to identify graphemes (e.g., ⟨a⟩).
• In epigraphy, used for mechanical transliterations of a text into the Latin script.
• In East Asian punctuation, used as quotation marks (e.g., ⟨quote⟩).
• In group theory, used for group presentations or ordered pairs and tuples (e.g., ⟨x, y⟩).
• In mathematics, used for Eulerian numbers of the second order (e.g., ⟨n, k⟩).
• In physics, used for expected value (e.g., ⟨x⟩).
• In quantum mechanics, used for the inner product in bra-ket notation (e.g., ⟨ψ|φ⟩).
• In continuum mechanics, used for Macaulay brackets (e.g., ⟨x⟩).
• In programming and ASCII, smaller and greater than symbols are used (e.g., < >).
• In programming, angle brackets are used to denote generics (e.g., in Java: List<String>).

24. Double Brackets ⟦ ⟧

• Used to indicate the semantic evaluation function in formal semantics for natural language and denotational semantics for programming languages.
• In the Wolfram Language, used for list indexing (e.g., ⟦x⟧).

25. Lenticular Brackets 【 】

• Used in East Asian languages for titles and headings (e.g., 【Title】).

26. Floor ⌊ ⌋ and Ceiling ⌈ ⌉ Brackets

• Used to denote the integer floor and ceiling functions (e.g., ⌊x⌋, ⌈x⌉).
• Used to denote continued fractions.

27. Quine Corners ⌜⌝ and Half Brackets ⸤ ⸥ or ⸢ ⸣

• Quine corners are used in mathematical logic for quasi-quotation or to denote the Gödel number of an expression (e.g., ⌜x⌝).
• Half brackets are used in English to mark added text, such as in translations (e.g., "Bill saw ⸤her⸥").
• In papyrological texts, half brackets enclose text missing due to damage (e.g., ⸤missing text⸥).

28. Brackets with Quills ⁅ ⁆

• Known as "spike parentheses," used in Swedish bilingual dictionaries to enclose supplemental constructions (e.g., ⁅example⁆).

29. Interrobang ‽

• Historical Context: The interrobang was invented in 1962 by Martin K. Speckter as a way to combine the question mark and exclamation point into a single character.
• The interrobang is not widely used but is sometimes seen in informal writing to express a rhetorical question or exclamation (e.g., "You did what‽").
• A combination of the question mark and exclamation point.
• Used to mark rhetorical questions or questions stated in a tone of disbelief (e.g., "You did what‽").
• In typography, the interrobang is used to add emphasis to a question that is also an exclamation (e.g., "What the heck‽").

30. Irony Point [Special Symbol] △ ψ

• Historical Context: The irony point was proposed in the 19th century as a way to indicate irony or sarcasm in written text. It has not been widely adopted.
• Used to indicate irony (e.g., "Oh, great △").
• The irony point is rarely used but can be found in some experimental or avant-garde writing (e.g., "Oh, great △").
• In informal writing, the irony point can be used to indicate sarcasm (e.g., "Sure, that's a great idea △").

31. Love Point [Special Symbol] ؟?

• Historical Context: Proposed in Hervé Bazin, in his essay "Plumons l'Oiseau" ("Let's pluck the bird", 1966). The love point is a playful punctuation mark used to express affection or love. It is not widely recognized but is sometimes used in informal writing.
• Used to express love or affection (e.g., "I love you ؟?").

32. Conviction Point [Special Symbol] (Barred !)

• Historical Context: Proposed in Hervé Bazin, in his essay "Plumons l'Oiseau" ("Let's pluck the bird", 1966). The conviction point was proposed as a way to express strong conviction or determination. It is not widely used but can be found in some experimental writing.
• Used to express strong conviction or determination (e.g., "We will win!").

33. Authority Point [Special Symbol] (Inverted Breve !◌̑)

• Historical Context: Proposed in Hervé Bazin, in his essay "Plumons l'Oiseau" ("Let's pluck the bird", 1966). The authority point was proposed as a way to express authority or command. It is not widely used but can be found in some experimental writing.
• Used to express authority or command (e.g., "Do it now!◌̑").

34. Acclamation Point [Special Symbol] \./

• Historical Context: Proposed in Hervé Bazin, in his essay "Plumons l'Oiseau" ("Let's pluck the bird", 1966). The acclamation point was proposed as a way to express acclamation or praise. It is not widely used but can be found in some experimental writing.
• Used to express acclamation or praise (e.g., "Bravo \./").

35. Doubt Point [Special Symbol] ?!

• Historical Context:Proposed in Hervé Bazin, in his essay "Plumons l'Oiseau" ("Let's pluck the bird", 1966). The doubt point was proposed as a way to express doubt or skepticism. It is not widely used but can be found in some experimental writing.
• Used to express doubt or skepticism (e.g., "Really?!").

36. Question Comma and Exclamation Comma ,! and ,?

• Used as question and exclamation marks within a sentence (e.g., "You're coming,? or You're coming,!").
• Normal question and exclamation marks can also be used for this purpose.

37. Snark Mark ~

• Historical Context: The snark mark was proposed as a way to indicate sarcasm or irony. It is not widely used but can be found in some experimental writing.
• Indicates an ironic statement by placing a tilde next to terminal punctuation:
• Dry sarcasm: .~
• Enthusiastic sarcasm: !~
• Sarcastic questions: ?~
• Variations include dry sarcasm (~.), enthusiastic sarcasm (~!), and sarcastic questions (~?).

38. SarcMark .@ {{}}

• Historical Context: The SarcMark was proposed by CollegeHumor as a way to indicate sarcasm. It is not widely used but can be found in some experimental writing.
• Proposed by CollegeHumor as "sarcastisies," resembling ragged or zig-zagged parentheses to enclose sarcastic remarks.
• A "SarcMark" symbol resembling a reversed @ with a period at its center was proposed in 2010.

39. Temherte Slaq ¡

• Historical Context:In Ethipopic languages it denoes sarcasm.
• Used at the end of a sentence with a sarcasm mark (e.g., "Oh, great ¡").

40. Percontation Point (؟)

• Historical Context: The percontation point or the rhetorical question mark was proposed by Henry Denham in 1580. It is not in common use today.
• A reversed question mark used for rhetorical questions (e.g., "You think so؟").

41. Indian Subheading ⟨:-⟩

• Used in place of a colon or after a subheading in Indian contexts.
• For monetary amounts, ⟨/-⟩ or ⟨/=⟩ is used (e.g., Rs. 20/- or Rs. 20/=).

42. Georgian Three Dots ⟨჻⟩

• Historical Context: The Georgian three dots were used as a sentence or paragraph divider in Georgian. They are still used in calligraphy.
• Formerly used as a sentence or paragraph divider in Georgian.
• Still used in calligraphy.

43. Armenian Punctuation

• Historical Context: Armenian punctuation has unique symbols that differ from Western punctuation. The full stop is represented by a colon, and the exclamation mark is represented by a diagonal similar to a tilde.
• The full stop is represented by a colon, and vice versa.
• The exclamation mark is represented by a diagonal similar to a tilde ⟨~⟩.
• The question mark ⟨՞⟩ resembles an unclosed circle placed after the last vowel of the word.

44. Greek Punctuation

• Historical Context: Greek punctuation has unique symbols that differ from Western punctuation. The question mark is written as the English semicolon, and the functions of the colon and semicolon are performed by a raised point.
• The question mark is written as the English semicolon.
• The functions of the colon and semicolon are performed by a raised point ⟨·⟩, known as the ano teleia.

45. Historical and Logographic Punctuation

• Punctuation marks were not needed in logographic or syllabic texts (e.g., Chinese and Mayan scripts).
• Ancient Chinese classical texts were transmitted without punctuation, but symbols like ⟨└⟩ and ⟨▄⟩ were used to indicate the end of a chapter or full stop.
• By the Song dynasty, punctuation became common to aid comprehension.

46. Inverted Interrobang ⸘

• Historical Context: The inverted interrobang was proposed as a mirrored version of the interrobang for languages like Spanish that use inverted punctuation at the beginning of questions/exclamations.
• Used in Spanish and other languages that use initial inverted punctuation (e.g., "⸘Qué estás haciendo⸘").
• Can be combined with regular interrobang for emphasis (e.g., "⸘¡¿Qué?!‽").

47. Section Sign §

• Historical Context: Originated in medieval manuscripts as a scribal abbreviation for the Latin word "sectiō".
• Used to reference numbered sections of documents (e.g., "See §3.2").
• In legal contexts, doubled (§§) indicates multiple sections.
• In some European countries, used as a paragraph marker.
• In mathematics, used to denote a section of a fiber bundle.

48. Pilcrow ¶

• Historical Context: Dates back to medieval manuscripts where it marked new thoughts (from Greek "paragraphos").
• Used to mark paragraphs in legal documents and manuscripts.
• In proofreading, indicates where a new paragraph should begin.
• In some word processors, displays hidden formatting marks.

49. Dagger † and Double Dagger ‡

• Historical Context: Originated in 14th century manuscripts to mark corrections.
• Used for footnotes when asterisk is already used († for first, ‡ for second).
• Mathematics and Physics:
  • Hermitian conjugate (A† for conjugate transpose)
  • Adjoint operator in functional analysis
  • Pseudoinverse of matrices
  • Creation/annihilation operators in quantum mechanics (a†)
• In biology, indicates extinct organisms (e.g., "Tyrannosaurus rex†").
• In genealogy, marks birth and death dates (†1850-‡1900).
• In linguistics, marks obsolete or reconstructed forms.
• In religious texts, indicates significant people or events.

50. Degree Symbol °

• Historical Context: First appeared in the 16th century in astronomical measurements.
• Used for angles (e.g., 90° right angle).
• Used for temperatures (e.g., 25°C, 77°F).
• Alcohol and Chemistry:
  • Alcohol proof (e.g., 40° = 20% alcohol by volume in some systems)
  • Primer (°), sexonder (°°), and tersier (°°°) alcohols in organic chemistry
  • Perfume/cologne alcohol percentage (e.g., Eau de Cologne = ~70° or 70% alcohol)
  • Baumé scale for liquid density (e.g., 10°Bé)
• In mathematics:
  • Indicates function composition (f°g)
  • Denotes degree of polynomial (deg f = n°)
  • In graph theory, vertex degree (deg(v) = 3°)
• In geographic coordinates (e.g., 40°N, 73°W).
• In typography, indicates superior ordinal numbers (1° = primo).

51. Prime ′ and Double Prime ″

• Historical Context: Evolved from Roman numeral notation in the 16th century.
• Used for feet and inches (e.g., 5′10″).
• Mathematical Uses:
  • Denotes derivatives (f′ for first derivative, f″ for second derivative)
  • Transformed coordinates (x′, y′ rotated coordinate system)
  • Dual spaces in linear algebra (V′ for dual space of V)
  • Transpose of a matrix (A′ or Aᵀ)
  • Complement of a set (A′)
  • In group theory, denotes derived subgroup (G′)
  • In number theory, sometimes indicates prime numbers (p′)
• In physics, marks transformed reference frames (x′ in relativity).
• In linguistics, marks stress or syllable boundaries.
• In astronomy, indicates arcminutes (′) and arcseconds (″).

52. Bullet •

• Historical Context: Used since the 18th century to create lists.
• Used for unordered list items.
• In mathematics, denotes multiplication or dot product.
• In chemistry, marks radical species (•OH).
• In linguistics, indicates reconstructed forms (•proto-word).

53. Therefore Sign ∴

• Historical Context: Used since the 18th century in mathematical proofs.
• Used in logical arguments and mathematical proofs.
• In chemistry, marks reaction yields.
• Alternative to :. in some proof notations.

54. Because Sign ∵

• Historical Context: Used alongside the therefore sign in formal logic.
• Used to indicate reasoning or causation.
• Common in mathematical proofs and logical arguments.

55. Reference Mark ※

• Historical Context: Originated in East Asian typography.
• Used in Japanese and Chinese texts as a footnote marker.
• Sometimes called "komastaru" in Japanese.
• Functions similarly to asterisk but more visually prominent.

56. Tie Symbol ⁀

• Historical Context: Developed for phonetic notation in the early 20th century.
• Used to connect letters in digraphs or diphthongs in phonetic transcription.
• In IPA, marks affricates or coarticulated consonants (e.g., [t⁀s] for "cats").
• In programming, represents string concatenation in some esoteric languages (e.g., "Hello"⁀"World" = "HelloWorld").
• In mathematical notation, connects related variables in tensor products (A⁀B).
• In some writing systems, joins compound characters or ligatures.

57. Undertie ‿

• Historical Context: Created for phonetic transcription.
• In IPA, indicates linking without pause between words.
• Used in some conlangs to mark vowel harmony.

58. Interpunct ·

• Historical Context: Used in ancient Latin as word separator.
• In Catalan, separates two Ls (l·l).
• In Japanese, separates foreign names (・).
• In mathematics, denotes dot product or decimal point.
• In chemistry, marks addition compounds (CuSO₄·5H₂O).

59. Commercial Minus ⁒

• Historical Context: Used in European accounting.
• Originally indicated debit balances.
• Now sometimes used in mathematics for symmetric difference.

60. Numero Sign №

• Historical Context: From Latin "numero" abbreviation.
• Used to indicate ordinal numbering.
• Common in Russian and other Slavic languages.
• In English often replaced with # (hash).