What are the most common grammar mistakes in academic writing?

The marks cluster on ten failures: subject-verb agreement (especially intervening nouns and one of the…), data treated as whichever form the house style rejected, outdated he or she after APA 7, CMOS 18, and MLA endorsed singular they, comma splices, Because… fragments, missing serial commas, that / which commas, dangling openers, unparallel lists (including not only… but also), and apostrophes in plurals. Start there before you hunt for exotic usage.

Is singular they allowed in APA, Chicago, and MLA?

Yes. In APA 7 it is endorsed (§4.18; student-paper checklist §§4.16–4.21). Write they are, not they is. Use a person’s stated pronouns, including they. CMOS 18 accepts generic singular they in formal writing (someone forgot their coat; each student should bring their own lunch) and already accepted referential they in the 17th edition. The MLA Style Center (4 March 2020) tells writers to follow stated pronouns (Jules… their research paper) and encourages generic they (Each taxpayer must file their tax return). If the course uses APA, Chicago, or MLA, do not “fix” they to he or she to look more formal.

Is data singular or plural in academic writing?

CMOS Q&A #364: treat data as a mass noun in common usage (less data) or as a plural in the sciences (fewer data). The same answer prefers fewer CO₂ emissions and less CO₂. AMA still supports the plural reading. Pick the journal’s form and keep it. Do not write the data shows in one paragraph and the data show in the next.

How do I fix a comma splice?

UNC: you cannot just add a comma between two complete sentences. Use a period, a semicolon, an em-dash, a comma plus and/but/or/so/yet/for/nor, or a subordinating word (because, although). However and therefore are not FANBOYS — they need a period or semicolon before them. If you are unsure the sentence is fused, try UNC’s yes/no and tag tests on the whole string.

Do I need the Oxford comma in an academic paper?

Yes if you are in APA, CMOS, or MLA. APA’s checklist: use a serial comma before the final element in a list of three or more. APA’s accessibility page and the MLA Style Center both reject the “use it only when needed” habit. UNC’s comma handout still calls that last comma optional in a short list; that is the writing-center outlier, not the handbook rule. AP news style is the other optional holdout. If the comma creates a new ambiguity, rewrite the sentence — do not drop the comma.

When do I use that versus which?

Default US academic rule, from the CMOS Q&A and UNC: that (no commas) restricts which thing you mean — Pizza that’s less than an inch deep; the paintings that hang in the SASB North lobby. Which (commas) adds extra information — Pizza, which is a favorite among Chicagoans; The Economic Growth and Tax Relief Reconciliation Act of 2001, which became law on June 7, 2001. That cannot open the extra-information clause. Who does the same job for people. Restrictive which without commas is tolerated in British English; do not treat it as the US classroom default.

What is a dangling modifier in a research paper?

MLA: the opener describes the wrong noun, or no noun at all. A renowned author, her work has received several awards leaves the author with nothing to modify. Using regression analysis, the data showed… makes the data the analyst. Tired and cranky, Jack’s morning cup of coffee… makes the coffee tired. Put the person or thing that actually did the action immediately after the comma, or rewrite so the opener is not needed. MLA’s exception is a phrase that modifies the whole situation: Given the weather conditions, schools and offices closed for the day.

Can I rely on Grammarly or a grammar checker?

Use it as a flag, then check the manual. UNC: grammar checkers work with a limited number of rules, miss errors, and give thin explanations. They are especially bad on current they rules, data, serial commas, and dangling openers, because those are style-manual decisions, not generic “correct English.”

How is this different from writing clearly or punctuating a citation?

Clarity is choosing a short verb and cutting jargon. Citation punctuation is where the period goes around a parenthesis. Grammar is whether the sentence is well-formed under APA 7, CMOS 18, or MLA 9. A crystal-clear comma splice is still a splice. Use the clarity guide for wordiness, the citation-punctuation guide for the period around (Author, year), and this page for agreement, clauses, modifiers, and required commas.

How should I proofread a paper for grammar?

UNC: edit structure first, proofread last. Get distance, proofread one error type per pass, read aloud, isolate sentences, and circle punctuation. A second reader beats a second software pass. UNC’s own proofreading handout plants seven intentional errors; use it as a drill, not as model prose. Then check the citation style the venue named — a clean sentence in the wrong documentation system still fails.

Common Grammar Mistakes in Academic Writing (APA 7, CMOS 18, MLA 9) [2026]

How to Fix Common Grammar Mistakes in Academic Writing: Quick Answer

Find the real subject and match the verb. Put a period, a semicolon, a dash, or a comma plus and/but/or/so between two complete sentences. Attach every Because… clause to an independent sentence. Use the serial comma in a list of three or more when the course follows APA, CMOS, or MLA — UNC’s comma handout is more flexible, the manuals are not. Keep a modifier next to the noun it describes. Do not let a grammar checker decide a current handbook rule. UNC’s editing and proofreading handout says those tools work from a limited rule set and often guess wrong.

Ten failures, with the official test

Agreement. Find the true subject, not the nearest noun. The collection of samples takes was, not were (template). APA 7 §4.15: the verb agrees in number with the subject. UNC: in one of the problems that…, the verb agrees with problems.
Data. CMOS treats data as a mass noun in common usage (less data) or as a plural in the sciences (fewer data). Do not force one form on every field.
Singular they. APA 7 §4.18, CMOS 18, and the MLA Style Center all accept generic and referential they. Write they are, not they is. Do not “correct” a person’s stated pronoun to he or she.
Comma splice / run-on. Two independent clauses need a period, a semicolon, a dash, or a comma plus a coordinating conjunction. A comma alone is a splice. UNC: you cannot just add a comma.
Fragment. A Because… clause is not a sentence until it is attached to an independent clause.
Serial comma. APA, CMOS, and MLA require the comma before the final and or or in a series of three or more. UNC treats that last comma as optional in a short list. Academic papers follow the assigned manual, not a news desk and not UNC’s optional default.
That / which. Restrictive clause: that (no commas) is the US academic default. Extra information: which (commas). That cannot open a non-restrictive clause.
Dangling modifier. MLA: a phrase that modifies nothing, or the wrong noun, dangles. A renowned author, her work… has no noun for the author to attach to.
Parallel lists. Every item in the series must share a grammatical shape. UNC: supporting…, reducing…, and education is the failure mode. MLA: not only sits after the verb that governs both items.
Apostrophes. MLA: it’s = it is; its is possessive. Plurals of names and weekdays take no apostrophe: The Wallaces, Sundays.

Repair templates (fill with your claim; labelled templates are not papers)

Agreement template, incorrect

The collection of samples were completed in March.

Agreement template, correct

The collection of samples was completed in March.

Clause-boundary template

Two complete thoughts: period, semicolon, dash, or comma + and/but/or/so. Not a comma alone.

Modifier template

Opening phrase + the person or thing that actually did it. Not the data, the paper, or the results.

What this page is (and is not)

Use this guide when a draft has a markable error: the verb does not match the subject, two sentences are glued with a comma, a dependent clause is standing alone, a modifier is attached to the wrong noun, or a list is missing the comma the assigned manual requires. How to write clearly is word choice and sentence rhythm. Active vs passive voice is which voice to pick. Revision strategies is the process. Format academic papers is headings, margins, and title pages. Punctuation in citations is where the period goes around a parenthesis. Keep those jobs off this URL.

The examples below come from pages we opened on 17 September 2026: the APA Style website (grammar hub; lists overview via the 21 September 2024 Wayback copy; singular-they page via the 29 December 2024 Wayback copy; accessible-typography page last updated February 2024 via Wayback), the APA student-paper formatting checklist PDF (© 2021; last updated 8 September 2021), the Alamo Colleges reprint of singular they (last updated 29 May 2026, 1:38 PM), CMOS Shop Talk (16 April 2024), the CMOS Q&A (still tagged to the 17th edition unless otherwise noted), University of Chicago News (21 February 2025), the MLA Style Center, and UNC Writing Center handouts. Live apastyle.apa.org HTML was Incapsula-blocked on this refresh. Invented journal articles, fake DOIs, and made-up studies do not appear here. Where a pattern is useful but no official sentence exists, the row is labelled as a template.

What the manuals actually say

Advice blogs still hedge on singular they and treat the serial comma as optional. The current handbooks do not. APA 7 (2020) puts grammar in Chapter 4 and lists in Chapter 6. CMOS 18 (2024) is the first Chicago edition to endorse generic singular they in formal writing. MLA 9 requires the serial comma in every series of three or more. The Style Center now has two grammar pages students actually need: five common grammar questions (29 December 2021) and How do I use singular they? (4 March 2020). The older version of this guide quoted APA and Chicago on they and left MLA as a hedge. That gap is closed here.

Official wording (keep these English in every locale)

APA Style, Singular “they” (§4.18; last updated July 2022)

The singular “they” is a generic third-person singular pronoun in English. Use of the singular “they” is endorsed as part of APA Style because it is inclusive of all people and helps writers avoid making assumptions about gender.

APA Style, Singular “they” (verb agreement)

Use a plural verb form with the singular pronoun “they” (i.e., write “they are” not “they is”).

APA Style student-paper checklist, Grammar (Publication Manual §4.15)

Use verbs that agree in number (i.e., singular or plural) with their subjects.

APA Style student-paper checklist, Pronouns (Publication Manual §§4.16–4.21)

Use the singular “they” when referring to a person who uses it as their self-identified pronoun or to a person whose gender is unknown or irrelevant.

CMOS Shop Talk (announcing CMOS 18)

The generic singular they will now be considered acceptable even in formal writing—for example, when the antecedent is an indefinite pronoun (someone forgot their coat) or when referring to a person whose gender is unknown or irrelevant (will the driver of the yellow sedan please move their car) or whose identity must be concealed (the author wants their privacy protected).

University of Chicago News, 21 February 2025 (CMOS 18)

Though the 17th edition of the Manual had previously endorsed the use of “they/them” as a personal pronoun, the newest edition now explicitly endorses the use of the generic singular “they” when referring to a person whose gender is unknown or unspecified (for example, each student should bring their own lunch).

MLA Style Center, How do I use singular they? (4 March 2020)

The MLA advises writers to always follow the personal pronouns of individuals they write about.

MLA Style Center, Serial Commas and Serial Semicolons

Proponents of the serial comma, like the MLA, would decry the inconsistency of the use-it-when-you-need-it approach and advocate using the serial comma in all series of three or more items or phrases.

APA Style, Accessible typography (Myth 6; last updated February 2024)

Not everyone calls for the serial comma: APA’s Publication Manual, the MLA Handbook, the Chicago Manual of Style, and Elements of Style require it, whereas The Associated Press Stylebook leaves it optional.

APA Style, student-paper formatting checklist

Use a serial comma before the final element in lists of three or more items.

Chicago Manual of Style Q&A (Usage and Grammar #364)

Even though “data” doesn’t look like a plural, you would write “less data” or “fewer data” depending on whether you consider “data” as a mass noun (as in common usage) or as a plural (as in the sciences).

Chicago Manual of Style Q&A (Which vs. That)

The basic rule: Use “which” plus commas to set off nonrestrictive (unnecessary) clauses; use “that” to introduce a restrictive (necessary) clause:

UNC Writing Center, Fragments and Run-ons

You CANNOT simply add a comma between the two sentences, or you’ll end up with what’s called a “comma splice.”

MLA Style Center, dangling modifiers

When a modifier modifies the wrong word or has nothing to modify at all, writing experts say that the modifier dangles.

APA Style, Lists

When writing a list, ensure all items are syntactically and conceptually parallel.

Chelsea Lee’s APA Style post Welcome, singular “they” (31 October 2019) is the publication-rule announcement that points to Publication Manual §4.18. CMOS Shop Talk published the 18th-edition they change on 16 April 2024. University of Chicago News restated it on 21 February 2025; the older /story/chicago-manual-style-updated-18th-edition URL now 404s. The live APA singular-they HTML page was Incapsula-blocked on this refresh; the §4.18 sentences above match the official-page Wayback copy (last updated July 2022) and the Alamo Colleges reprint of the same Style Center wording (last updated 29 May 2026).

Subject-verb agreement (including data and one of the)

The verb agrees with the head of the subject, not with a noun in a prepositional phrase and not with the nearest plural. Intervening words are the usual trap. APA’s checklist restates Publication Manual §4.15 in one sentence. A labelled template, then the UNC relative-clause cases that students actually miss:

Head noun, not the nearest noun (templates)

Template, incorrect

The collection of samples were completed in March.

Template, correct

The collection of samples was completed in March.

Template, incorrect

Each of the participants were given a questionnaire.

Template, correct

Each of the participants was given a questionnaire.

Each is singular even when a plural noun follows. The subject of the first pair is collection, not samples.

The UNC relative-clauses handout is the official worked case for one of the… constructions. The verb in the relative clause agrees with the noun the relative pronoun replaces — problem (singular) or problems (plural) — not with one.

UNC Writing Center (relative clauses)

UNC, plural

People who win the lottery are lucky. (plural verb)

UNC, singular

A person who wins the lottery every year is lucky. (singular verb)

UNC, that agrees with problem

Homelessness is a problem that needs to be addressed. (singular problem)

UNC, that agrees with problems

Homelessness is one of the problems that need to be addressed. (plural problems)

Is data singular or plural?

The old classroom rule “data is always plural” is no longer the whole story. The CMOS Q&A on *less* vs *fewer* treats data two ways and gives both official example sentences. The same answer prefers fewer with a plural noun (fewer CO₂ emissions) and less with a mass noun (less CO₂). Match the house style of the journal or lab: many science editors still want the plural verb; CMOS allows the mass-noun reading in ordinary prose. Be consistent inside one paper. The Q&A is still tagged to CMOS 17 unless otherwise noted; the data pair did not change in the 18th-edition announcement.

Chicago Manual of Style Q&A #364

CMOS, data as mass noun

We had a lot less data to support our hypothesis than we wanted. [data as mass noun]

CMOS, data as a plural noun

The second group of researchers returned fewer data than the first. [data as a plural noun]

CMOS, emissions (official preference)

fewer CO₂ emissions, but less CO₂ (carbon dioxide is a mass—or noncount—noun: CO₂ is; CO₂ emissions are)

CMOS: the latter usage, including fewer, is the one AMA Manual of Style (10th ed., §7.8.2) supports. The same answer says lower emissions is a good alternative; less emissions will not satisfy sticklers.

Latin pairs still split in formal writing: criterion / criteria, phenomenon / phenomena, medium / media. Write the criteria are and this criterion is. Do not treat criteria as a singular.

Pronouns: singular they is no longer a hedge — including in MLA

The 2026-08-30 version of this page said APA 7 and CMOS 18 endorse singular they and left MLA as a silence. That is incomplete. The MLA Style Center’s How do I use singular they? (published 4 March 2020) tells writers to follow a person’s stated pronouns and encourages generic they so the sentence does not invent a gender. APA 7 §4.18 endorses generic they. CMOS 18 endorses generic they in formal writing. Both already required referential they when a person uses those pronouns. The failure mode now is the opposite of 2015: do not “correct” they to he or she on a paper that follows APA, Chicago, or MLA.

MLA Style Center (singular they)

MLA, specific use

Jules is writing their research paper on Jane Austen’s Persuasion.

MLA, specific use, reflexive

Ari read the instructions to themselves [or themself] before beginning the test.

MLA, generic (do not invent a gender)

Each taxpayer must file his or her tax return before 15 April.

MLA, generic, singular they

Each taxpayer must file their tax return before 15 April.

MLA, generic, they after When a celebrity

When a celebrity joins Twitter they gain tens of thousands of followers within minutes.

MLA, anonymous reviewer

The anonymous reviewer recommends in their report that the essay be published after minor revisions.

MLA, Everyone

Everyone wants to do well on their midterm.

MLA: for generic uses, writers should not use he or she alone or alternate he and she. A plural recast or a pronoun-free rewrite is also acceptable. Do not use those workarounds to avoid a person’s stated they.

APA Style and CMOS 18 (what to write)

APA / CMOS 18, generic (official CMOS example)

someone forgot their coat

APA / CMOS 18, generic (UChicago News example)

each student should bring their own lunch

APA Style, official form table (Casey)

Casey is a gender-fluid person. They are from Texas and enjoy tacos.

APA verb form

they are (not they is)

APA noun form

Casey is or a person is (not Casey are or a person are)

Do not invent a gender

Do not use he as a generic. APA: do not use combination forms such as (s)he or s/he. Use he or she only when those pronouns actually match the people being described.

When they feels awkward

APA allows a rewrite that drops the pronoun, or a plural recast (Students must submit their assignments). Do not use those workarounds to avoid a person’s stated they.

Unclear antecedents are still an error. If they could mean either the researchers or the participants, name the noun. That is a reference problem, not a reason to ban singular they.

Unclear antecedent (template)

Template, unclear

The researchers discussed the results with the participants, and they were satisfied.

Template, clear

The researchers discussed the results with the participants, and the participants were satisfied.

Comma splices, run-ons, and FANBOYS

The UNC fragments-and-run-ons handout and the UNC commas handout are the worked cases. A complete sentence needs a subject, a predicate, and a complete thought. Two of those in a row need a real boundary. A comma is not that boundary. UNC’s shortest complete sentence is They waited. UNC also lists an em-dash as a legal run-on repair; a comma is still not.

UNC Writing Center (run-on and comma splice)

UNC, shortest complete sentence

They waited.

UNC, run-on (fused sentence)

My favorite Mediterranean spread is hummus it is very garlicky.

UNC, semicolon

My favorite Mediterranean spread is hummus; it is very garlicky.

UNC, comma + coordinating conjunction

My favorite Mediterranean spread is hummus, and it is very garlicky.

UNC, two sentences

My favorite Mediterranean spread is hummus. It is very garlicky.

UNC, subordinating conjunction

My favorite Mediterranean spread is hummus because it is very garlicky.

UNC, em-dash

My favorite Mediterranean spread is hummus—it is very garlicky.

UNC, comma splice (the illegal “fix”)

My favorite Mediterranean spread is hummus, it is very garlicky.

If you are not sure the sentence is a run-on, UNC reprints Rei R. Noguchi’s two tests from Grammar and the Teaching of Writing: turn the sentence into one yes/no question, then into one tag question. A complete sentence survives both tests. A fused sentence does not.

UNC / Noguchi tests (official hummus pair)

UNC, yes/no on a complete sentence

Is my favorite Mediterranean spread hummus?

UNC, tag on a complete sentence

My favorite Mediterranean spread is hummus, isn’t it?

UNC, the fused sentence fails the single-question test

Is my favorite Mediterranean spread hummus is it very garlicky?

UNC’s comma handout uses FANBOYS — for, and, nor, but, or, yet, so — as the only coordinating conjunctions that can join two independent clauses with a comma. However, therefore, and moreover are conjunctive adverbs. They take a period or a semicolon before them and a comma after, not a comma on both sides of a splice. The same handout rejects two comma myths: a long sentence does not automatically need a comma, and a pause in your breath is not a comma test.

UNC Writing Center (commas)

UNC, comma splice

My hamster loved to play, I gave him a hula-hoop.

UNC, second splice

You wore a lovely hat, it was your only defense.

UNC, FANBOYS repair

You wore a lovely hat, for it was your only defense.

UNC, conjunctive adverb, correct

Basketball is my favorite sport; however, table tennis is where I excel.

UNC, conjunctive adverb, also correct

Basketball is my favorite sport. However, table tennis is where I excel.

UNC, conjunctive adverb, incorrect

Basketball is my favorite sport, however, table tennis is where I excel.

Sentence fragments

UNC: the fragments students miss are dependent clauses. They have a subject and a verb, so they look finished, but a subordinator (because, after, when, since, if, although) leaves the thought incomplete. Attach the clause to an independent sentence, or drop the subordinator. UNC’s test question after a lone Because… clause is still What did they do?

UNC Writing Center (fragments)

UNC, fragment

Because their car was in the shop.

UNC, complete (clause first)

Because their car was in the shop, they took the bus.

UNC, complete (clause second)

They took the bus because their car was in the shop.

UNC, fragment (time)

After the rain stops

UNC, fragment (condition)

When you finally take the test

Template, -ing fragment

Fragment: The participants ranging in age from 18 to 65. Complete: The participants ranged in age from 18 to 65.

Serial commas: APA, CMOS, and MLA agree — UNC is the flexible outlier

In a series of three or more, put a comma before the final and or or if the paper follows APA, CMOS, or MLA. APA’s lists overview requires the comma (or a semicolon when an item already contains commas) before the final item. The accessible-typography page (last updated February 2024) calls optional serial commas a myth: the Publication Manual, the MLA Handbook, CMOS, and The Elements of Style require the comma; AP Style leaves it optional. UNC’s commas handout is the one academic page that still says the last comma is optional in a short, simple list and required only when the items get long. That is a writing-center convenience, not the APA / MLA / CMOS rule. If the assigned manual is one of those three, keep the comma. If the comma creates a new ambiguity, rewrite — do not drop the comma.

Official serial-comma examples

APA Style, accessible typography (no serial comma)

Jiji the cat likes sleeping in the sun, cuddles and treats.

APA Style, accessible typography (serial comma)

Jiji the cat likes sleeping in the sun, cuddles, and treats.

APA Style, Tasha is not the sister

I bought presents for my sister, my father, and Tasha.

APA Style, Tasha is the sister

I bought presents for my father and my sister, Tasha.

APA Style, rewrite rather than drop the comma

I play basketball with Lebron James, Sheryl Swoops, and my son.

MLA Style Center, ambiguous without the comma

Lia ordered three smoothies: strawberry, peach and mango and pineapple.

MLA Style Center, why that sentence fails

Without a serial comma placed after peach or after mango, it isn’t clear if “peach and mango” is one flavor or if “mango and pineapple” is.

MLA Style Center, second ambiguity

Sam took his dog for a walk and ran into Deirdre, a friend and his dentist.

The MLA Style Center’s serial commas and serial semicolons page (15 June 2017; the older /serial-commas-and-serial-semicolons/ URL now 404s) also points to a real overtime case: Daniel Victor’s 16 March 2017 *New York Times* report on the Maine truck-driver dispute. MLA’s point is not that one lawsuit rewrote the handbook. It is that “use the comma only when needed” is the habit that created the ambiguity. When the items already contain commas, bump the separators up to semicolons. That is the same rule on APA’s lists page, the MLA Style Center’s Suzette Tanner example, and UNC’s semicolons handout.

Official serial-semicolon examples

UNC Writing Center, semicolons

I bought shiny, ripe apples; small, sweet, juicy grapes; and firm pears.

MLA Style Center, four speakers

The invited speakers are the association’s president; the vice president; the councilwoman, Suzette Tanner; and Walter McCarthy, the executive director.

Relative clauses: that versus which

The academic default is the CMOS Which vs. That Q&A and UNC’s relative-clauses handout. A restrictive clause identifies which noun you mean; it takes that and no commas. A non-restrictive clause adds extra information; it takes which (or who) and commas on both sides. That cannot open a non-restrictive clause. Two nuances the short rule hides: UNC accepts which in a restrictive clause (some readers object; that is preferred). CMOS says using which restrictively is “more or less okay” in British English if you leave the commas off. US academic papers should still default to that for the necessary clause. The Q&A still cites CMOS 17 §§6.27 and 5.250; Shop Talk’s 18th-edition list did not rewrite the that / which pair.

Official that / which examples

CMOS Q&A, official rewrite of the tax-act sentence

The Economic Growth and Tax Relief Reconciliation Act of 2001, which became law on June 7, 2001, is the largest change in tax regulations in over two decades.

CMOS Q&A, restrictive

Pizza that’s less than an inch deep just isn’t Chicago-style.

CMOS Q&A, non-restrictive

Pizza, which is a favorite among Chicagoans, can be either bad for you or good, depending on how much of it you eat.

CMOS Q&A, restrictive which (British, no commas)

Pianos which have a fourth pedal to mute the strings are popular among apartment owners.

UNC, restrictive

I like the paintings that hang in the SASB North lobby.

UNC, non-restrictive

My mother, who is an excellent cook, is thinking of opening a restaurant.

UNC, not okay

I’m planning to grow roses, that I find quite beautiful.

UNC, okay

I’m planning to grow roses, which I find quite beautiful.

Dangling modifiers

The MLA Style Center and its five common grammar questions are the official worked cases. A modifier at the start of a sentence has to describe the next noun. If that noun is not the person or thing doing the action, the phrase dangles. The old template on this page (Using regression analysis, the data…) is still the failure mode; the rows below are MLA’s own sentences. MLA’s one named exception: a phrase can modify the situation of the whole sentence (Given the weather conditions, schools and offices closed for the day.) rather than the next noun.

MLA Style Center (dangling modifiers)

MLA, five common questions, dangling

A renowned author, her work has received several awards.

MLA, five common questions, attached

A renowned author, she has received several awards for her work.

MLA, five common questions, exception

Given the weather conditions, schools and offices closed for the day.

MLA, pizza dangler

Topped with pepperoni and covered with extra cheese, the children devoured the pizza.

MLA, pizza revised

Topped with pepperoni and covered with extra cheese, the pizza was devoured by the children.

MLA, no agent

Turning the corner, a house came into view.

MLA, agent supplied

As we turned the corner, a house came into view.

MLA, mid-sentence dangler

Class participation should be considered when giving final grades in the course.

MLA, mid-sentence revised

Instructors should consider class participation when giving final grades in the course.

MLA, adjective dangler

Tired and cranky, Jack’s morning cup of coffee got him through the day.

MLA, adjective revised

Tired and cranky, Jack needed his morning cup of coffee to get him through the day.

MLA, like dangler

Like most office workers these days, our in-boxes are filled with e-mail.

MLA, as dangler

As a dancer, your feet need proper care.

MLA, as revised

As a dancer, you need to take proper care of your feet.

Template, research opener

Dangling: Using regression analysis, the data showed significant trends. Attached: Using regression analysis, we found significant trends in the data.

Parallel structure

The UNC parallelism handout says a series should share one grammatical shape. APA’s lists page says the same thing: items must be syntactically and conceptually parallel. The student-paper checklist restates it for Publication Manual §§6.49–6.52: ensure items in lists are parallel; use commas in simple lists and semicolons when any item already contains commas. Faulty parallelism is not always ungrammatical, but it is the list that reads as if the last item came from a different sentence. MLA’s extra trap is correlative conjunctions: not only has to sit after the verb that governs both items.

UNC Writing Center and MLA Style Center (parallelism)

UNC, not parallel

The three pillars of the Mayor’s campaign are supporting local business, reducing crime, and education.

UNC, parallel gerunds

The three pillars of the Mayor’s campaign are supporting local business, reducing crime, and increasing educational funding.

UNC, parallel nouns

The three pillars of the Mayor’s campaign are local business development, crime reduction, and education.

UNC, non-parallel terms

The study included teenagers, people in their thirties, and octogenarians.

UNC, parallel terms

The study included people in their teens, in their thirties, and in their eighties.

MLA, not only too early

John not only noticed Bob’s new car but also Bob’s new toupee.

MLA, not only after the governing verb

John noticed not only Bob’s new car but also Bob’s new toupee.

Apostrophes, hyphens, and the because-comma

MLA’s five common grammar questions is the official short list. Apostrophes mark possession or a contraction, not a plural. Hyphenate a pair of words only when they work together as an adjective before a noun. After a negative statement, a comma before because can stop the not from swallowing the reason. Joseph Wallace’s 26 January 2022 Style Center reply is honest about the limit: this is not an ironclad rule if the sentence is already unambiguous. Use the comma when the not could attach to the reason.

MLA Style Center (apostrophes, hyphens, because)

MLA, contraction versus possessive

“It’s” is a contraction of “it” and “is,” and “you’re” is a contraction of “you” and “are.” “Its” is the possessive form of “it,” and “your” is the possessive form of “you.”

MLA, no apostrophe in the plural

For family names and any other proper noun, leave out the apostrophe to make them plural: “The Wallaces,” “Sundays.”

MLA, hyphenate the compound adjective

In phrases like “problem-solving strategies” and “event-planning guidelines,” hyphens make sense.

MLA, do not hyphenate the noun phrase

I have seen references to “the world-order,” “advanced problem-solving,” and “event-planning.” But these phrases don’t need hyphens.

MLA, ambiguous because after a negative

He did not learn anything that day because he was asleep in class.

MLA, comma before because

He did not learn anything that day, because he was asleep in class.

CMOS 18 also changed one colon rule that still trips students who learned CMOS 17: Shop Talk’s announcement says the first word of a grammatically complete sentence after a colon now takes an initial capital. UNC’s semicolons, colons, and dashes handout is more flexible — it lets either capital or lowercase stand if you stay consistent — so a Chicago paper should follow CMOS 18, not UNC’s optional pair. Decade plurals and initialism plurals still take no apostrophe. The rows below are usage templates — they are not quotations from a paper.

Apostrophe and colon templates (not official sample papers)
Incorrect template	Correct template	Rule
1990's	1990s	No apostrophe for a plural year
PhD's	PhDs	No apostrophe for a plural initialism
its'	its (possessive) / it's (it is)	Its is possessive; it's = it is
who's theory	whose theory	Whose is possessive; who's = who is
your'e	you're (you are) / your (possessive)	Do not mix the contraction with the possessive
The finding is this: the effect vanished.	The finding is this: The effect vanished.	CMOS 18: capitalize a complete sentence after a colon

These pairs still generate marks. The examples are templates. For data, use the CMOS pair above rather than a third invented sentence.

Confusable-word templates
Pair	Academic default	Template
affect / effect	Affect is usually the verb; effect is usually the noun	The treatment affected the outcome. The effect was large.
than / then	Than compares; then marks time	Group A scored higher than Group B. We collected the responses, then coded them.
ensure / insure	Ensure = make certain; insure = insurance	The protocol was written to ensure consistency.
principal / principle	Principal = main; principle = rule	The principal finding. The ethical principles.
different from / different than	Academic default is different from	The revised scale is different from the original.
based on / based off of	Use based on	The codebook was based on the interview guide.

Discipline notes that are still grammar

Tense and bias-free wording sit next to grammar because a correct sentence can still violate the house rule. These are not a second clarity guide. They are the errors that survive a spell-check. University of Chicago News also records two CMOS 18 capitalization shifts that look like “style” until an editor marks them: Indigenous is now capitalized when it refers to people, and Black is usually capitalized. APA’s checklist restates Publication Manual §4.12: keep verb tense consistent in the same and adjacent paragraphs.

Field habit	What to write	What not to treat as optional
IMRaD methods and results	Past tense for what you did and what you found; present tense for a standing claim	Do not drift into literary present in the results table
Literature (MLA classrooms)	Literary present: Hamlet says, not Hamlet said, for the text on the page	Keep historical events in past tense
APA papers	Bias-free language in Chapter 5, including singular they (§4.18 / §5.5)	Do not default to he for a generic participant
Science editors	Often keep data plural (the data show)	Do not switch from data are to data is mid-paper
CMOS 18 prose	Capitalize a complete sentence after a colon; capitalize Indigenous for people	Do not keep a CMOS 17 lowercase after a full-sentence colon

Proofread one error type at a time

UNC’s editing and proofreading handout separates editing (argument, structure, evidence) from proofreading (surface grammar and punctuation). Proofread last. Distance helps: put the draft down, change the look of the page, or hand it to a first-time reader. Grammar checkers are optional assistants, not the manual. The same handout plants seven intentional errors in its own prose so you can practice; do not treat those planted slips as UNC’s recommended wording.

UNC proofreading moves that catch grammar

Do not rely entirely on spelling checkers. They miss your / you're, to / too, and there / their.
Treat grammar-checker flags as hypotheses. UNC: the programs work with a limited number of rules and often make mistakes.
Proofread for only one kind of error at a time.
Read slowly, and read every word. Read aloud so you hear the clause boundaries.
Separate the text into individual sentences, or isolate each line with a ruler.
Circle every punctuation mark and ask whether it is required.
Read backward word by word for spelling; sentence by sentence for grammar.
Look up the case you are not sure about. UNC’s test question is still Should you use “that” instead of “which”?

Before you submit

Every verb agrees with the real subject, including one of the… clauses
Data, criteria, and phenomena are consistent with the house style
Singular they is used where APA 7, CMOS 18, or MLA require it; no leftover generic he
No comma splices; however is not joining clauses with commas alone
No dependent-clause fragments
Every series of three or more has the serial comma if the assigned manual is APA, CMOS, or MLA (or serial semicolons when an item already has commas)
Restrictive clauses use that without commas; extra information uses which with commas
Opening modifiers attach to the next noun; no A renowned author, her work…
Lists are parallel; not only sits after the governing verb
Apostrophes are possessive or contracted, never plural years, PhDs, or Sundays
The draft has been read aloud after a break

Frequently asked questions

What are the most common grammar mistakes in academic writing?: The marks cluster on ten failures: subject-verb agreement (especially intervening nouns and one of the…), data treated as whichever form the house style rejected, outdated he or she after APA 7, CMOS 18, and MLA endorsed singular they, comma splices, Because… fragments, missing serial commas, that / which commas, dangling openers, unparallel lists (including not only… but also), and apostrophes in plurals. Start there before you hunt for exotic usage.
Is singular they allowed in APA, Chicago, and MLA?: Yes. In APA 7 it is endorsed (§4.18; student-paper checklist §§4.16–4.21). Write they are, not they is. Use a person’s stated pronouns, including they. CMOS 18 accepts generic singular they in formal writing (someone forgot their coat; each student should bring their own lunch) and already accepted referential they in the 17th edition. The MLA Style Center (4 March 2020) tells writers to follow stated pronouns (Jules… their research paper) and encourages generic they (Each taxpayer must file their tax return). If the course uses APA, Chicago, or MLA, do not “fix” they to he or she to look more formal.
Is data singular or plural in academic writing?: CMOS Q&A #364: treat data as a mass noun in common usage (less data) or as a plural in the sciences (fewer data). The same answer prefers fewer CO₂ emissions and less CO₂. AMA still supports the plural reading. Pick the journal’s form and keep it. Do not write the data shows in one paragraph and the data show in the next.
How do I fix a comma splice?: UNC: you cannot just add a comma between two complete sentences. Use a period, a semicolon, an em-dash, a comma plus and/but/or/so/yet/for/nor, or a subordinating word (because, although). However and therefore are not FANBOYS — they need a period or semicolon before them. If you are unsure the sentence is fused, try UNC’s yes/no and tag tests on the whole string.
Do I need the Oxford comma in an academic paper?: Yes if you are in APA, CMOS, or MLA. APA’s checklist: use a serial comma before the final element in a list of three or more. APA’s accessibility page and the MLA Style Center both reject the “use it only when needed” habit. UNC’s comma handout still calls that last comma optional in a short list; that is the writing-center outlier, not the handbook rule. AP news style is the other optional holdout. If the comma creates a new ambiguity, rewrite the sentence — do not drop the comma.
When do I use that versus which?: Default US academic rule, from the CMOS Q&A and UNC: that (no commas) restricts which thing you mean — Pizza that’s less than an inch deep; the paintings that hang in the SASB North lobby. Which (commas) adds extra information — Pizza, which is a favorite among Chicagoans; The Economic Growth and Tax Relief Reconciliation Act of 2001, which became law on June 7, 2001. That cannot open the extra-information clause. Who does the same job for people. Restrictive which without commas is tolerated in British English; do not treat it as the US classroom default.
What is a dangling modifier in a research paper?: MLA: the opener describes the wrong noun, or no noun at all. A renowned author, her work has received several awards leaves the author with nothing to modify. Using regression analysis, the data showed… makes the data the analyst. Tired and cranky, Jack’s morning cup of coffee… makes the coffee tired. Put the person or thing that actually did the action immediately after the comma, or rewrite so the opener is not needed. MLA’s exception is a phrase that modifies the whole situation: Given the weather conditions, schools and offices closed for the day.
Can I rely on Grammarly or a grammar checker?: Use it as a flag, then check the manual. UNC: grammar checkers work with a limited number of rules, miss errors, and give thin explanations. They are especially bad on current they rules, data, serial commas, and dangling openers, because those are style-manual decisions, not generic “correct English.”
How is this different from writing clearly or punctuating a citation?: Clarity is choosing a short verb and cutting jargon. Citation punctuation is where the period goes around a parenthesis. Grammar is whether the sentence is well-formed under APA 7, CMOS 18, or MLA 9. A crystal-clear comma splice is still a splice. Use the clarity guide for wordiness, the citation-punctuation guide for the period around (Author, year), and this page for agreement, clauses, modifiers, and required commas.
How should I proofread a paper for grammar?: UNC: edit structure first, proofread last. Get distance, proofread one error type per pass, read aloud, isolate sentences, and circle punctuation. A second reader beats a second software pass. UNC’s own proofreading handout plants seven intentional errors; use it as a drill, not as model prose. Then check the citation style the venue named — a clean sentence in the wrong documentation system still fails.

Grammar is not the citation style

A grammatically clean paper still fails if the documentation is in the wrong system. Match APA, MLA, or Chicago, then check each record against the manual. Use the clarity guide for wordiness, the voice guide for active versus passive, and the citation-punctuation guide for the period around a parenthesis.

Citation generator →Which citation style? →Write more clearly →