Punctuation, Spelling, and Style

In This Section


Common examples of appropriate punctuation, capitalization, spelling, and general usage are provided here to help you prepare your manuscript according to AIAA style. Be advised that accepted manuscripts also are copyedited and formatted by our production team to further ensure uniformity of style and usage across articles published in a journal, and sometimes an author’s style preferences are changed for the sake of consistency. You will have the opportunity to review changes and respond to queries when you receive the final proofs. For more complete guidance on grammar and spelling, AIAA also recommends the latest editions of Chicago Manual of Style and Merriam Webster’s Collegiate Dictionary, both of which are available online.

Colons, Semicolons, and Dashes
Quotation Marks
Using Italics
Parentheses and Other Enclosures
Plurals and Possessives
Spelling and Hyphenation
Abbreviations and Acronyms
Preferred Style and Usage
Computer Terminology
  • Generally, commas are used around, before, and after nonrestrictive clauses and phrases. A nonrestrictive clause or phrase is one that is informative but not essential to the meaning of the sentence.
  • Commas also may be logically used in pairs to set off dependent clauses where particular emphasis or clarity is required (e.g., “Wall chamber damage was an interesting, if unwelcome, result.” Or., “Note that, when going from Eq. (18) to Eq. (19), the pairs of events shown are statistically independent of each other.”
  • The use of commas following a short introductory phrase is optional, but there are many common words and phrases that always use a comma at the beginning of a sentence: For example, Furthermore, In general, That is, In particular, Nonetheless, Moreover, Therefore, Hence, and others.
  • Always insert a comma following a long introductory phrase.
  • Items in a series are normally separated by commas. When a conjunction, usually and or or, joins the last two elements in a series of three or more, a comma (known as the serial comma) should appear before the conjunction.
  • When independent clauses are joined by andbutorsoyet, or any other coordinating conjunction, a comma usually precedes the conjunction. If the clauses are very short and closely connected, the comma may be omitted (unless the clauses are part of a series). 
  • When a dependent clause precedes the main independent clause, it should be followed by a comma. A dependent clause is generally introduced by a subordinating conjunction such as ifbecause, or when.
  • When a conjunction is used together with “if” (but if, that if, and if) a comma is not needed between the two conjunctions, unless misreading can result.
  • Don’t follow that with a comma when the subsequent phrase or clause is restrictive, that is, essential to the meaning of the sentence  (e.g., “It was understood that given the aforementioned conditions, a positive result was unlikely.”)
  • Use a comma before which when the subsequent phrase or clause is nonrestrictive (e.g., “The engine used radially inward quadlet injectors, which now pointed directly at the centerbody.”)
  • Use commas with a series of adjectives where the order of the adjectives can be reversed without affecting the meaning (e.g., “Visible plume length caused the chamber to be redesigned as a single, longer, uniform piece.”)
  • Use commas in numbers of five or more digits (12,000) but not four digits (2000). An exception is made in tables when alignment of columns is affected (2,000 if table also includes five-digit numbers).
  • Always set off these expressions with commas: i.e., e.g., etc., Inc., Ltd., and the words respectively and however.
  • Use commas preceding a coordinating conjunction (andbutorso, for, nor, yet) to separate the parts of compound sentences. Compound sentences comprise independent clauses that tie together similar ideas where each clause can stand alone as a complete thought.
  • Unless misreading will result, do not use a comma before a conjunction that separates two verbs with the same subject: “The missile launch was successful and cleared the way for future funding” (where there is no comma before “and”).
  • Parallel dependent clauses also do not use a comma before the conjunction: “Analysis of Figure 4 indicates that the midlatitude values are insignificant for this parameter and that high-latitude values are quite divergent.”
  • Do not use a comma preceding the suffixes Jr., II, III, etc. In the reference list, however, where the name is inverted, do use a comma: Doe, J.S., Jr. (Note that the suffix “Jr.” is placed after the initials.)
Colons, Semicolons, and Dashes
  • Use a colon in a sentence only if a period also would be correct: “This is true for the following reasons: …” but no colon in “This is true because….”
  • Pay particular attention to the proper use of colons in figure captions and in sentences immediately preceding displayed equations or numbered lists.
  • Use a semicolon to separate parts of a compound sentence where the two independent clauses can stand as separate sentences but where the related ideas will benefit from staying connected.
  • Conjunctive adverbs such as however, thus, hence, accordingly, therefore are preceded by a semicolon (and followed by a comma).
  • Semicolons may be used to separate subcaptions for multiple-part figures.
  • Use semicolons to separate the parts of a list if commas are used within one or more of the parts. In this case, use of a conjunction before the final entry in the list may be appropriate.
  • Colons and semicolons should be placed outside of quotation marks and superscript reference numbers.
  • Avoid using dashes in scholarly writing. Pairs of dashes can be replaced with commas or parentheses, and colons are preferred in place of a single dash introducing a separate thought or a list.  A colon also is preferable to a dash in the paper title or in section headings.
  • If you use hyphens to indicate a range of numbers in your manuscript, they will be changed to “en-dashes” (–) during copyediting: April 10–12, 6–8 ft, Figs. 2–4, etc.
  •  Do not use a dash in a “between…and” or a “from…to” construction: “The frequencies ranged from 2 to 6 s.”
  • If you use hyphens to join entities of equal weight linked in a common context, they will be changed to en-dashes during copyediting: man–machine interface, pressure–time history, U.S.–Japan conference, Newton–Raphson equation, red–blue, free–free, proportional–integral derivative.
  • An en dash also can be used to join a prefix to an open compound; e.g., pre–Cold War.
Quotation Marks
  • Use quotation marks around direct quotes in your manuscript.
  • Quotations longer than 50 words will be indented and set as block quotes in the final published paper.
  • Only use sets of single quotation marks for quotes within a quote.
  • Quotation marks may be used to coin a term for a specific use in your manuscript when the term is first introduced. If the term is used again, the quotation marks are not used.
  • Never use quotation marks for words or terms following so-called.
  • Place closing quotation marks aftercommas and periods but before colons and semicolons.
Using Italics
  • Italics strictly used for visual emphasis is discouraged. Never use italics for long phrases, as a complete sentence, or for whole paragraphs.
  • You may use italics to define or introduce a key term or ranges on a scale: “Because RDE’s ideally rely on combustion in a detonative mode, there can be overmixing, which leads to….”  “In this case, the relationship is tangential ….” Or, “The results ranged between 3.25 (important) and 0.01 (not important) for the cases being studied.” After the term has been introduced to the reader, do not continue to italicize it.
  • Singular headings within your manuscript such as Theorem, Proof, Lemma, Remark, etc., may be italicized and followed by a colon or a period depending on the substance of the statement or paragraph, but be consistent in usage throughout the manuscript.
  • Names unique to a specific aircraft or space vehicle are italicized, following naval convention for names of ships.
  • Refer to the Guidelines for Mathematics for proper use of italics within equations.
Parentheses and Other Enclosures
  • If a parenthetical expression is used at the end of a sentence, the period must be placed after the closing parenthesis. The opening parenthesis never is preceded by a comma or other punctuation.
  • If a complete sentence is enclosed in parentheses, it must begin with a capital letter and end with a period inside closing parenthesis. A citation such as “(see Fig. 2)” is treated as a parenthetical expression, not as a complete sentence.
  • Use brackets for a parenthetical remark that already contains parentheses, such as “[see Eq. (4)].”
  • In reference citations, always use brackets in the following manner: [1], [1, 2], [1–3, 5].
  • In citations for equations, always use parentheses in the following manner: Eqs. (1) and (3) [not Eqs. (1 and 3)]; Eqs. (1), (3), and (6) [not (1, 3, 6)]; Eqs. (1–3) [not (1)–(3)].
  • Do not use parentheses to enclose parts of figures: Figs. 2a and 2b [not Figs. 2(a) and 2(b)].
  • Use a single parenthesis following each number in a list: “The cases are 1) isotropic, 2) elastic, and 3) inelastic.” When referring back to listed elements, however, do not include the single parenthesis: “In case 1 we …” not “In case 1) we….”
  • The hierarchy for enclosures within a sentence is { [ ( ) ] }. The use of parentheses, brackets, and braces for mathematical expressions may be similar but will be determined by the intended meaning.
Plurals and Possessives
  • Do not use apostrophes to form the plural of acronyms and numbers: UAVs, 2000s. Note that the plural “s” is lowercase when used with an acronym. Also, do not add an “s” if the last word of the acronym or abbreviation is not plural, such as AOA (angles of attack) or rpm (revolutions per minute).
  • Do not add “ ’s” to mathematical symbols or units of measure: “The various ci indicate that …,” “At a force of 3 g …,” etc.
  • Apostrophes precede the “s” for singular possessives. Add a second “s” to create possessives of singular words (not plural) and names that already end in “s”: Jones’s theory, not Jones’ theory, but the missiles’ trajectories.
  • Capitalize prepositions with five or more letters in headings and titles, including titles of references.
  • Particles that are part of proper names (de, du, la, von, van, etc.) may be capitalized or lowercased depending on the individual’s preference or native practice. All, however, should be capitalized if they begin a sentence.
  • Do not capitalize numbered terms such as model 4, column 6, sample 3, type 2, region 8. On the other hand, do capitalize parts within a manuscript such as Table 6, the Appendix, Theorem 3, and so forth.
  • Capitalize only the element that is the proper name for laws, numbers, and similar expressions, such as Ohm’s law or the Reynolds number.
  • Trademark-protected names, such as Plexiglas, must be capitalized. The symbols ® or™ may be used the first time the trademark appears, although such use is not required so long as the term is properly capitalized.
Spelling and Hyphenation
  • Use shorter forms of most words that have alternative spellings: analog not analogue, equaled not equalled, modeling not modelling, judgment not judgement, acknowledgment not acknowledgement.
  • Use American spelling, not British: color not colour; analyze not analyse.
  • Commonly used compound words that formerly were hyphenated are now frequently written as one word: buildup, crossover, cutoff, output, stepwise, counterexample, airstream breakpoint, etc. (Note that when used as verbs many of these examples become two words.)
  • Words with prefixes that used to be hyphenated now are written as one word, even those with double vowels or consonants: nonporous, multidimensional, nonnegative, subbody, semiconductor, reentry.
  • There are important exceptions when closing up prefixes. Hyphenate double vowels with semi and multi (semi-illuminated, multi-output); hyphenate all prefixes that are separated from the second half of a compound (over- and underused). Hyphenate prefixes when combined with more than one word (quasi-one-dimensional, non-time-dependent).
  • spell quasi open as a noun compound but hyphenate as an adjective (quasi steady-state system, quasi-public corporation).
  • Compound modifiers (also called phrasal adjectives) such as high-profile, one-dimensional, and real-time precede a noun, and hyphenation usually lends clarity. It is never incorrect to hyphenate adjectival compounds before a noun. When such compounds follow the noun they modify, hyphenation is usually unnecessary.
  • Compound modifiers that signify relative size or position (high, intermediate, medium, middle, large, low, long, short, small, etc.) should be hyphenated. Hyphens are not needed when the compound is combined with an adverb, however (high-frequency waves vs very high frequency waves).
  • Don’t use a hyphen when the first word of a compound modifier is an“-ly” adverb: rapidly increasing attenuation. Compounds that include comparative adverbs such as more, most, very, least also are not hyphenated.
  • Phrases that act as attributive modifiers usually are hyphenated for clarity (month-by-month improvement, order-of-magnitude change, day-to-day comparison, one-to-one relationship, charged-particle fluctuations).
  • Numerals in combination with units of measure or with “by” or “x” are not hyphenated: 3 × 9 ft plane, 2 in. long pipe, 10–20 km wide area, 33 m distance, 6 mm diam tube.
  • For clarity, use hyphens for homographs and to avoid misreading of real words: un-ionized. Use hyphens when the prefixes or suffixes are combined with proper names or numbers: non-Newtonian, pre-1945.
  • Hyphenate ordinal numbers in combination with nouns: nth-order equation, second-order equation.
  • In general, use words for single-digit numbers (including zero), and use numerals for two or more digits; exceptions are noted next.
  • Use numerals for all of the numbers in self-contained lists with varying digits: 6, 12, and 100 particles; 4 cones and 16 cylinders.
  • Numbers used as parts of nouns are written as numerals: case 3, 2:3 ratio, value of 6.
  • Numbers preceding units of measure or chemical abbreviations are always written as numerals, except at the beginning of a sentence.
  • Days, months, weeks, and years, if smaller than 10 and not primary measurements within a manuscript, are described in words in the main text: five days, two years. (Use numerals in tables or figures.)
  • Except for years, spell out numerals at the beginning of a sentence, or recast the sentence to avoid stilted wording.
  • Spell out ordinals smaller than 10, including “zeroth.” Variables that represent ordinals should be followed by “th” without a space or a hyphen (e.g., ith, nth.)
  • Insert a 0 (zero) before a decimal point for numbers less than 1 (e.g., 0.6, never .6.)
  • In text and in tables, use 106 instead of 1,000,000; Reynolds number is alwayswritten as Re = 3 × 106 instead of 3,000,000; or Re = 1.3 x 106 instead of 1,300,000.
  • Use standard (Arabic) numerals (not roman numerals) throughout, including tables, figure and equation numbers, and for volume, issue, and chapter numbers in reference lists.
Abbreviations and Acronyms
  • An abbreviation for a single word should be lowercase and unpunctuated unless misreading could result: vs for versus, av for average, const for constant, max for maximum, min for minimum, but long. for longitude and in. for inches.
  • Only “vs” from the preceding list is abbreviated regularly in the text. The remainder of these examples should be abbreviated only when they are used in mathematical expressions.
  • Acronyms always are spelled out in full the first time they are used in the text and are followed by the initials in all-capital letters enclosed in parentheses. Don’t assume that an acronym that seems common to you will be familiar to the reader.
  • When acronyms are spelled out, only proper names or trademarks need to be capitalized. It is not necessary to show how an acronym was derived by use of italic or underscored letters, or a mixture of capital and lowercase letters, within each word.
  • Acronyms and abbreviations in figure captions and table headings may be used so long as they are defined somewhere in the text.
  • Abbreviate 2-D, 3-D, including hyphens, for two-dimensional, three-dimensional, and so forth.
  • Do not spell out complicated chemical abbreviations. (Retain dashes where needed and use numerals for numbers under 10.)
  • Common Latin abbreviations such as e.g., i.e., and cf. are best reserved for parenthetical statements if you choose to use them. Using their spelled-out English forms in running text (for example, that is, etc.) is preferred in formal writing. When citing a reference with more than two authors, et al. may be used in regular text.
  • Abbreviate academic degrees (M.S., Ph.D., etc.) and use periods as shown here.
  • Use the following standard abbreviations (or their plural forms) before numbers: Eq., Fig., Sec. Spell them out in full, however, when they begin a sentence.
  • Do not abbreviate equation if it is part of an expression: “The state equations (3–6) ….” Note that mathematical expressions also may be labeled as something other than an equation: matrix (7), inequality (4), functions (2) and (3).
  • Do not begin a sentence with a lowercase symbol or with an abbreviation. When a reference begins a sentence, do not use the abbreviation “Ref.” Instead use Reference [4] or use the author’s name.
  • Spell out Air Force Base in full in the affiliation and the main text but abbreviate it (AFB) in the reference list, tables, and figure captions.
  • Use the diam abbreviation for diameter in combination with units: 3 ft diam plane. Do not abbreviate diameter when it is separated from the unit or if it represents a unit: 3 ft in diameter, 3 diameters.
  • Abbreviate units of measure when used with numbers; spell them out in full, however, when used without a specific value: “a few centimeters,” not “a few cm.”
  • Spell out all months in the main text and in footnotes. Use the following abbreviations in references and tables: Jan., Feb., Aug., Sept., Oct., Nov., Dec.
  • Use country abbreviations U.K. and U.S. only as modifiers.
Preferred Style and Usage
  • The plural tense of the verb is used for “data”: data are, not data is.
  • Change while to although or whereas, unless “at the same time” or “during” is the intended meaning.
  • Do not begin a sentence with Due to or Due to the fact that; change to Because. Within a sentence, “due to,” when used to mean “caused by” or “attributed to,” is correct.
  • Use based on to modify a noun, as in, “The results based on Johnson’s theory show ….” Use on the basis of when the verb is being modified: “On the basis of Johnson’s theory we found …” not, “Based on Johnson’s theory we found ….”
  • In regular text change since to because unless the passage of time is being indicated; following convention in mathematics, “since” is acceptable when introducing an equation.
  • Substitute before for prior to.
  • Change in order to at the beginning of a sentence (and frequently at the beginning of a clause within a sentence) to simply to.
  • Shorten more importantly, when used as an introductory phrase, to more important, where the adjective form is needed to indicate that one fact is more important than another. Reserve the “-ly” adverb form for cases where something is being done in an important manner.
  • Use full, formal versions of words: photograph, not photo.
  • Use regular type, not italic, for foreign terms and Latin expressions (e.g.,carte blanche, fait accompli, et al., in situ, a priori).
  • Use regular type for all names of space programs, satellites, missiles, and planetary spacecraft, with the exception of names that are unique to individual aircraft or space vehicles, which are italicized following naval convention for names of ships.
  • Always use that (or who/whom/whose) to introduce a restrictive or essential clause: “The missile that was launched in May 1996 was the first in the series.” Use which to introduce a nonrestrictive or parenthetical clause: “The missile, which was launched in May 1996, was the first in the series.” Nonrestrictive clauses can be omitted without changing the meaning of the sentence, and they are set off from the rest of the sentence by commas.
  • Use compared to when the purpose is to liken two things or to put them in the same category. Use compared with when the purpose is to place things side by side to examine their differences or similarities.
  • Use composed of (made up of or constituting) or comprises or comprising (includes/encloses or including/enclosing), but never comprised of.
  • Use ensure when the meaning is to make certain of, use insure when the meaning is to protect against a loss, and use assure when the meaning is to convince.
  • Affect is a verb meaning to influence (“the budget constraints will not affect missile performance”), and effect is a noun referring to the influence on something or the result of something (“the study showed the effect of 0 g on humans”). “Effect” also is used to mean “bring about,” as in “to effect a settlement.”
  • Use preceding or next to refer to elements within a manuscript (the preceding section, the next equation); use previous to refer to earlier works (the previous literature). Avoid above and below.
  • Replace utilize with use.
  • Expressions that include proper names are not always possessive (e.g., the Prandtl number). Those that are possessive should not be preceded by an article (“a,” “the”), as in “Young’s modulus.
Computer Terminology
  • Processes and products for which acronyms have been derived should be spelled out in full when they are first used, unless they are extremely common [e.g., multi-input/multi-output (MIMO), CD-ROM].
  • Names of computer software and programming languages are typeset in capital letters if they are acronyms: FORTRAN. Otherwise follow the established spelling and capitalization: Python, JavaScript.
  • Use small caps or lowercase according to the syntactic rules of each language for computer coding, including names of algorithms, routines, subroutines, and commands (e.g., IF/THEN, GO TO, printf, mov).
  • The font you choose for computer code displayed in your manuscript can be distinguishable from the regular text; be mindful of the column width in the final PDF format of the published article if you want to include guidance for where line breaks are acceptable in lines of code.
  • Computer code names and algorithm names that are acronyms do not need to be spelled out in titles, headings, or the text (e.g., POST, MUSCL, LAURA).