Common Grammar Mistakes

Grammar mistakes do not only affect grades on student essays. They undermine job applications, erode confidence in research reports, create ambiguity in legal documents, and cause readers to question the writer’s competence before they question the argument. A reader who stumbles on three comma splices in the opening paragraphs of a dissertation is already doubting the analysis—unfairly, but predictably. Grammar is not the measure of intelligence; it is the contract between writer and reader that keeps attention where it belongs: on the ideas, not the errors.

This guide covers the full spectrum of common grammatical errors—from the structural mistakes that fracture sentences to the word-level confusions that quietly distort meaning. Each section explains what the error is, why it happens, how to identify it, and how to correct it. The examples are drawn from academic essays, business communications, and general writing, because the same errors appear across all contexts. Whether you are proofreading a research paper, editing a professional report, or building grammar confidence from the ground up, the coverage here is designed to be genuinely useful—not a list of rules to memorize but an explanation of why language works the way it does.

For writers who need professional support beyond self-editing, our proofreading and editing service provides expert review of grammar, style, and structure across all document types.

Subject-Verb Agreement: The Error Beneath the Surface

Subject-verb agreement is one of the most fundamental rules in English grammar, and one of the most frequently violated—not because writers do not know the basic principle but because sentence complexity creates distance between the subject and its verb, allowing the wrong form to slip through unchallenged. The rule itself is simple: a singular subject takes a singular verb; a plural subject takes a plural verb. Enforcing it becomes harder as sentences grow longer and more elaborate.

Intervening Phrases

The most common trigger for subject-verb agreement errors is an intervening phrase between subject and verb—typically a prepositional phrase that introduces a noun different in number from the true subject. The verb must agree with the grammatical subject, not with the nearest noun.

Collective Nouns

Collective nouns—words like team, committee, faculty, jury, government, and staff—refer to groups and cause consistent agreement uncertainty. In American English, collective nouns are almost always treated as singular: the group is considered a single unit acting together. In British English, collective nouns are more commonly treated as plural when the members of the group are acting individually. The key is internal consistency within any single document.

Indefinite Pronouns

Indefinite pronouns create persistent agreement problems because their grammatical number is not always obvious. Some are always singular, some are always plural, and a small group can be either depending on context.

Always Singular	Always Plural	Either (context-dependent)
everyone, everyone, anyone, no one, someone, everybody, anybody, nobody, somebody, each, either, neither, one	few, many, several, both, others	all, some, most, any, none (depends on the noun they refer to)
Everyone is welcome Everyone are welcome	Few were present Few was present	“All of the water is gone” (water = mass noun = singular) “All of the students are gone” (students = countable = plural)

Compound Subjects

When two subjects are joined by and, the compound subject is usually plural and requires a plural verb. When subjects are joined by or, nor, either…or, or neither…nor, the verb agrees with the subject closest to it—a rule called the “proximity rule.”

Pronoun Errors: Agreement, Reference, and Case

Pronoun errors fall into three distinct categories that are often conflated: agreement errors (the pronoun and its antecedent do not match in number or gender), reference errors (it is unclear which noun the pronoun refers to), and case errors (the wrong pronoun form is used based on its grammatical function). Each requires a different diagnostic and a different fix.

Pronoun Reference Errors

A pronoun reference error—sometimes called ambiguous pronoun reference—occurs when it is unclear which noun a pronoun refers to. This is a precision problem: the sentence is grammatically defensible but semantically ambiguous.

Pronoun Case Errors

Case errors occur when a pronoun is used in the wrong grammatical function. The most common appear in compound constructions, where the addition of another noun or pronoun causes writers to lose track of the correct form.

Apostrophe Misuse: Possession, Contraction, and the Plural

Apostrophe errors are so common they have earned cultural notoriety—the “greengrocer’s apostrophe” (apple’s, orange’s) has become shorthand for a particular kind of written carelessness. Yet the rules governing apostrophe use are among the most consistently applied in English punctuation, and learning them removes an entire category of error permanently.

The Three Uses of the Apostrophe

Its vs. It’s — The Most Frequent Confusion

The most persistent apostrophe error in English writing is confusing its and it’s. The logic that trips writers up: possessive nouns take apostrophes (“the cat’s paw”), so possessive pronouns should too. They do not. Possessive pronouns—his, her, its, our, their, whose—never take apostrophes. The apostrophe in it’s signals only the contraction of “it is” or “it has.”

Quick test: Substitute “it is” wherever you have written it’s or its. If “it is” makes sense, use it’s with the apostrophe. If it does not, use its without.

Possession Rules in Full

Noun Type	Rule	Example
Singular noun	Add ‘s	the student’s essay, the manager’s report, Charles’s decision
Plural noun ending in s	Add apostrophe only	the students’ essays, the managers’ reports, the companies’ profits
Irregular plural (not ending in s)	Add ‘s	the children’s books, the women’s team, the people’s choice
Joint possession	Add ‘s to last noun only	Sarah and Marcus’s project (shared project)
Separate possession	Add ‘s to each noun	Sarah’s and Marcus’s projects (separate projects)
Possessive pronouns	No apostrophe ever	its, their, whose, ours, yours, hers, his

Comma Errors: Overuse, Omission, and Misplacement

Comma errors span a spectrum from devastating (the comma splice) to subtle (the missing Oxford comma that changed the meaning of a legal contract), but all of them create friction between writer and reader. The comma is the most versatile—and therefore the most misunderstood—punctuation mark in English. Its functions are many: separating items in a list, joining independent clauses with a coordinating conjunction, setting off introductory elements, enclosing non-essential information, and more. Errors arise when writers apply commas intuitively rather than functionally.

The Oxford Comma (Serial Comma)

The Oxford comma is the comma placed before the final conjunction in a list of three or more items. Its use is a matter of style in general writing—the AP Stylebook omits it; the Chicago Manual of Style requires it—but in academic and professional writing, the Oxford comma prevents ambiguity and is strongly recommended by most academic publishers.

The Comma After Introductory Elements

A comma should follow introductory elements—adverbial clauses, long prepositional phrases, participial phrases, and transitional expressions—before the main clause begins. Omitting this comma creates sentences that readers must re-parse.

Non-Restrictive vs. Restrictive Clauses

One of the most consequential comma decisions involves relative clauses introduced by which or that (and sometimes who). A restrictive clause limits or defines the noun it modifies—it cannot be removed without changing the sentence’s essential meaning. It takes no commas. A non-restrictive clause adds supplementary information that could be removed without altering the core meaning. It is set off by commas.

A useful shortcut: which typically introduces non-restrictive clauses and is set off by commas; that typically introduces restrictive clauses and takes no commas. This distinction—though not absolute in all varieties of English—holds reliably in formal academic and professional writing.

Comma Splices and Run-On Sentences

Identifying Independent Clauses

An independent clause contains a subject and a verb and expresses a complete thought—it could stand alone as a sentence. When two independent clauses appear in the same sentence, their connection must be signaled through one of three mechanisms: a semicolon; a coordinating conjunction preceded by a comma (for, and, nor, but, or, yet, so—remember the acronym FANBOYS); or a subordinating conjunction that converts one clause into a dependent clause.

Four Ways to Fix a Comma Splice

Sentence Fragments: Incomplete Thoughts That Appear Complete

A sentence fragment is a group of words punctuated as a sentence—beginning with a capital letter and ending with a period—that does not, in fact, contain a complete sentence. A complete sentence requires a subject, a finite verb, and the expression of a complete thought. Fragments fail on at least one of these counts.

Fixing Fragments

Fragments are fixed by either attaching the fragment to an adjacent complete sentence or by supplying the missing element to create a standalone sentence. The approach depends on whether the fragment is an orphaned subordinate clause, a verbless phrase, or a subjectless predicate.

Dangling and Misplaced Modifiers

Modifier errors are among the most entertaining grammar mistakes—entertaining, that is, to everyone except the writer. A dangling modifier is a descriptive phrase that either has no logical subject in the sentence or attaches logically to the wrong subject. A misplaced modifier is a word, phrase, or clause positioned far enough from the noun it modifies that the relationship is unclear or absurd.

Dangling Modifiers: The Pattern

Dangling modifiers almost always follow the same pattern: an introductory participial or infinitive phrase, followed by a main clause whose subject is not the doer of the action in the phrase. The phrase “dangles” because the noun it should logically attach to is absent from the sentence or is not the grammatical subject of the main clause.

Misplaced Modifiers

A misplaced modifier is positioned too far from the word it modifies, attaching itself inadvertently to the wrong noun and producing unintended—sometimes absurd—meanings. The fix is almost always to move the modifier closer to what it is meant to describe.

For academic writers, misplaced modifiers most often appear with limiting adverbs (only, just, nearly, almost, even, merely). The rule is to place these adverbs immediately before the word or phrase they limit, not a word or two away from it. Misplacing only is among the most statistically common modifier errors in scholarly prose according to writing instructors across disciplines.

Commonly Confused Word Pairs: Meaning, Not Just Spelling

Homophones and near-homophones—words that sound alike or similar but differ in spelling and meaning—produce errors that spellcheckers routinely miss because both spellings are valid words. The confusion is semantic, not orthographic: the writer uses a word that exists but is not the word they mean. This category of error is particularly problematic in academic writing because it can distort argument and, unlike spelling mistakes, is invisible to automated tools.

The Merriam-Webster usage resources provide authoritative guidance on disputed word pairs and usage questions—a valuable reference for writers uncertain about specific distinctions. The guidance below covers the pairs that appear most consistently in student and professional writing.

Their / There / They’re

Your / You’re

Complement / Compliment

Principal / Principle

Cite / Site / Sight

Word	Part of Speech	Meaning	Example
Cite	Verb	To quote or reference as evidence; to summon officially	“Cite all sources in APA format.”
Site	Noun	A location; a website	“The research site was a public library.”
Sight	Noun / Verb	Vision; the act of seeing; something seen	“The sight of the data confirmed the hypothesis.”

Affect, Effect, Fewer, Less, Further, Farther

These three pairs represent usage distinctions that appear in virtually every piece of formal writing and generate consistent errors even among experienced writers. Understanding them removes a source of credibility-undermining mistakes in academic essays, research reports, and professional communications.

Affect vs. Effect

A reliable test: substitute “influence” (a verb) and “result” (a noun) into your sentence. If “influence” fits, use affect. If “result” fits, use effect. “The policy influenced the outcome” → “The policy affected the outcome.” “The policy’s result was delayed” → “The policy’s effect was delayed.”

Fewer vs. Less

This is a countability distinction. Fewer applies to nouns you can count as individual units—discrete, enumerable items. Less applies to uncountable or mass nouns—quantities measured rather than counted. The error almost always runs in one direction: less used where fewer is correct.

Farther vs. Further

Who vs. Whom, Lay vs. Lie, Comprise vs. Compose

Who vs. Whom

Who and whom are relative and interrogative pronouns whose forms follow the same case logic as subject and object pronouns: who = subject (like “he,” “she,” “they”); whom = object (like “him,” “her,” “them”). The confusion is a case confusion dressed in grammatical vocabulary.

The standard test: rephrase the clause as a statement and substitute he/him or she/her. If the substitute is a subject pronoun (he, she, they), use who. If the substitute is an object pronoun (him, her, them), use whom.

Lay vs. Lie

This pair causes more confusion than almost any other verb pair in English, partly because their past tense forms overlap and partly because the distinction between transitive and intransitive verbs is not something most people think about consciously. Lay is a transitive verb: it takes a direct object. Something is always being laid down by someone. Lie is intransitive: it takes no direct object. Something lies on its own without being placed by anyone.

Verb	Present	Past	Past Participle	Example
Lay (transitive)	lay	laid	laid	“She laid the report on the desk.” (laid = past tense of lay)
Lie (intransitive)	lie	lay	lain	“The report lay on the desk all morning.” (lay = past tense of lie)

The overlap that generates errors: the past tense of lie (intransitive) is lay—the same form as the present tense of lay (transitive). So “She lay down to rest” is correct (past tense of intransitive lie), while “She laid down to rest” is incorrect (no direct object—this cannot be transitive).

Comprise vs. Compose

This pair involves a directional distinction: the whole comprises the parts; the parts compose the whole. Comprise means “to be made up of” or “to include.” The subject of comprise is the whole; its object is the parts. Compose means “to make up” or “to form.” The subject of compose is the parts; its object is the whole.

Parallel Structure Failures

Parallel structure—also called parallelism—is the principle that grammatically equivalent elements in a series, comparison, or list should take equivalent grammatical forms. When a list shifts unexpectedly from one grammatical form to another, the reader experiences a jarring inconsistency that disrupts both comprehension and the impression of analytical rigor. Parallel structure errors are especially common in academic writing because complex sentences with multiple coordinated elements are standard.

Parallel Structure in Comparisons

Comparisons using than, as…as, more…than, and similar constructions also require parallel elements on both sides. The items being compared must be grammatically equivalent and logically comparable.

Correlative Conjunctions Require Parallel Structure

Correlative conjunctions—both…and, either…or, neither…nor, not only…but also, whether…or—must be followed by grammatically equivalent forms. Whatever grammatical structure follows the first element of the pair must mirror what follows the second.

Tense Consistency Errors

Tense consistency errors—also called tense shifts—occur when a piece of writing moves unpredictably between verb tenses without a logical reason for the change. Some tense shifts are appropriate: moving from past tense to present tense to discuss the current implications of a historical event, for example, or using the historical present to narrate a sequence of events. Inappropriate tense shifts occur when the writer changes tense within a single narrative thread without intending to mark a change in time frame.

Academic Writing Tense Conventions

Different sections of academic documents follow different tense conventions, and mixing them inappropriately is a common source of tense errors in student writing. Understanding the conventions by section prevents the most frequent errors.

Document Section	Standard Tense	Rationale
Literature review	Past tense for completed studies; present tense for established facts or ongoing relevance	“Smith (2020) found that…” / “This approach is well-established in the field.”
Methods	Past tense	Describes what was done: “Participants were recruited through…”
Results	Past tense	Reports what was found: “The analysis revealed…”
Discussion	Present tense for interpretation; past for referring back to findings	“These results suggest that…” / “The correlation we identified…”
Conclusions	Present tense	States current understanding: “This study demonstrates…”
Abstract	Past tense for method and findings; present for implications	“Data were collected from…” / “The findings have implications for…”

The Purdue Online Writing Lab’s grammar resources provide comprehensive guidance on tense usage in academic contexts—a reliable reference for writers developing discipline-specific writing conventions. For subject-specific academic writing support, our academic writing service covers every discipline and document type.

Passive Voice: When It Harms and When It Helps

The instruction to “avoid the passive voice” is one of the most frequently issued and most frequently misunderstood pieces of writing advice. Passive voice is not grammatically incorrect. It is a stylistic choice with legitimate uses and genuine risks. Understanding the distinction between appropriate and inappropriate passive constructions is more useful than a blanket avoidance rule.

What Passive Voice Actually Is

A passive construction reverses the subject-object relationship of an active sentence. In the active voice, the grammatical subject performs the action: “The researcher conducted the interviews.” In the passive voice, the grammatical subject receives the action: “The interviews were conducted by the researcher.” The agent (the researcher) moves to a by-phrase or disappears entirely: “The interviews were conducted.” This disappearance of agency is the feature that makes passive voice problematic in some contexts and useful in others.

Semicolons, Colons, and Dashes: The Misunderstood Three

These three punctuation marks are powerful tools for writers who understand them—and consistent sources of error for those who approximate their use intuitively. Each has a specific function that cannot be freely substituted.

The Semicolon

A semicolon has two primary uses: joining two closely related independent clauses without a coordinating conjunction, and separating items in a list when those items themselves contain commas (the “super-comma” function).

The Colon

A colon introduces what follows—a list, a quotation, an explanation, or an elaboration—and signals that what follows fulfills or explains what precedes it. The most important rule: a complete independent clause must precede a colon. A colon cannot follow a verb, a preposition, or a transitional phrase that leaves the opening clause incomplete.

Dashes: Em Dash and En Dash

English uses two dash lengths for different purposes. The em dash (—) is longer and more emphatic: it sets off a parenthetical element (like commas, but with more emphasis), marks an abrupt interruption, or introduces a restatement or elaboration. The en dash (–) is shorter and used for ranges (pages 14–28, 2019–2023) and compound adjectives where one element is a range or open compound (the New York–based firm, a Nobel Prize–winning researcher).

Double Negatives and Redundancy

Double negatives and redundant expressions both undermine writing precision—one by logical confusion, the other by verbal inflation. Both are common, and both are correctable with careful editing.

Double Negatives

In standard English, two negatives produce a positive (or at minimum a logical muddle). “I don’t have no data” means, literally, that you do have data—the double negative cancels itself. In academic and professional writing, double negatives are always errors. They typically arise from combining a negative verb with a negative pronoun (nothing, nobody, nowhere) or a negative adverb (never, hardly, scarcely, barely).

Note: “I can’t help but wonder” and “not uncommon” are not double-negative errors—they are established constructions with their own accepted meanings. “Not uncommon” means “somewhat common,” expressing moderate frequency with deliberate understatement.

Redundancy and Pleonasm

Redundancy refers to using more words than necessary to express a single idea—either by repeating the same meaning in different words (pleonasm) or by including words that add no information. Redundancies make writing verbose without adding clarity or depth. They are especially common in business and academic writing where writers attempt to sound thorough.

Redundant Expression	Reason	Concise Version
advance planning	“planning” is by definition in advance	planning
end result	“result” is always an end	result
past history	“history” refers to the past	history
future prospects	“prospects” concern the future	prospects
completely unique	“unique” means one of a kind—cannot be modified by degree	unique
basic fundamentals	“fundamentals” are already basic	fundamentals
final conclusion	conclusions are final	conclusion
free gift	gifts are free by definition	gift
period of time	“period” means a span of time	period
added bonus	bonuses are additions	bonus
first and foremost	means the same thing twice	first
each and every	same meaning duplicated	each / every

Capitalization Errors: Rules and Common Violations

Capitalization errors fall into two directions: under-capitalization (failing to capitalize proper nouns, titles, and the beginnings of sentences) and over-capitalization (capitalizing common nouns, generic job titles, and abstract concepts that do not warrant it). Both appear regularly in student writing; over-capitalization is the more common error in professional business writing.

What Must Be Capitalized

• Proper nouns: specific names of people, places, organizations, brands, and events—”the University of Edinburgh,” “the World Health Organization,” “the Renaissance,” “Tuesday,” “March”
• Titles used as names: when a title precedes a name or is used as a form of address—”Professor Chen,” “Director Williams,” but “the professor” and “the director” when used generically
• First word of a sentence: always, including the first word after a colon that introduces a complete sentence (style-dependent)
• Abbreviations and acronyms: WHO, NASA, APA, GDP—though the spelled-out versions are often not all capitalized: “World Health Organization”
• Specific course and document titles: “Introduction to Behavioral Economics” (course title) vs. “a course in economics” (generic reference)

Common Over-Capitalization Errors

The rule of thumb: if you would capitalize the word regardless of which specific thing it referred to, it is a common noun and should not be capitalized. “Department” is over-capitalized when it refers to a department generally; it is correct when it refers to a named department: “the Department of Psychology.” The Chicago Manual of Style, the most widely used style authority for academic book publishing, provides detailed capitalization guidance across its dedicated chapter on the subject—an essential reference for writers working under Chicago-style requirements.

Articles: A, An, and The — Where Writers Go Wrong

For native English speakers, article errors are rare because article usage is absorbed unconsciously through language acquisition. For non-native speakers writing in English, articles represent one of the most persistent and structurally complex areas of the language because many major world languages—including Chinese, Japanese, Korean, Russian, Arabic, and Hindi—use no articles at all or use them very differently. Even for native speakers, certain article rules are counterintuitive enough to cause errors.

The A / An Distinction

The choice between a and an depends on the sound that begins the following word, not the letter. An precedes words that begin with a vowel sound (including silent consonants); a precedes words beginning with a consonant sound (including words that begin with a vowel letter but a consonant sound).

Definite vs. Indefinite Articles

The (definite article) refers to a specific, identifiable thing—one the speaker and reader both know or have established. A/an (indefinite article) introduces a non-specific instance of a countable noun. The distinction matters for precision: “The study” refers to a specific study already identified in context; “a study” refers to any one study of its type. Using the without having previously established the referent creates a false familiarity—the reader is implicitly required to know which specific thing is meant when they do not.

Preposition Myths and Real Preposition Errors

Two rules about prepositions dominate writing instruction despite being demonstrably incorrect as universal prohibitions: the rule against ending a sentence with a preposition, and the rule against splitting infinitives. Understanding why these “rules” are myths—and where genuine preposition errors actually occur—produces more accurate and more fluent writing.

The Ending-Preposition Non-Rule

The prohibition against ending sentences with prepositions originated from Latin grammar, where prepositions cannot be separated from their objects. English is not Latin. English has always permitted sentence-final prepositions, and many natural English constructions require them. Avoiding them produces sentences more awkward than the alleged error they prevent. Winston Churchill’s famous observation captures the absurdity perfectly: “This is the sort of English up with which I will not put.”

Real Preposition Errors: Wrong Preposition Choice

While terminal prepositions are not errors, choosing the wrong preposition for a given verb or adjective is. English verbs and adjectives often pair with specific prepositions, and using the wrong one is a genuine error that can distort meaning or mark writing as non-native.

Expression	Correct Preposition	Common Error
interested in	interested in the results	interested about the results
different from	different from the control group	different than the control group (in formal British/academic usage)
comply with	comply with the regulations	comply to the regulations
independent of	independent of the other variables	independent from the other variables
responsible for	responsible for the outcome	responsible of the outcome
superior to	superior to the alternative	superior than the alternative
based on	based on the evidence	based off the evidence

Grammar in Academic and Professional Writing Contexts

Grammar errors in academic writing carry consequences beyond the sentence level. Markers and examiners who encounter frequent errors—particularly higher-order errors like comma splices, fragment abuse, subject-verb disagreement, and parallel structure failures—evaluate them as evidence of insufficient editing care, and sometimes as evidence of insufficient analytical control. The assumption—fair or not—is that a writer who cannot control sentences may not fully control their argument.

High-Stakes Grammar Errors by Document Type

For academic documents specifically, the discipline’s style guide provides the authoritative reference for grammar conventions that vary by field. APA style, for example, has specific requirements about the use of the singular “they,” reporting statistics, and the use of first-person. Chicago Manual style has different conventions for fiction versus non-fiction. MLA style used in humanities has its own grammar and formatting expectations. Understanding which style guide governs your document is part of understanding the grammar standards you are writing to. Our essay writing service and dissertation writing service apply the correct style guide standards for every submission.

Revising for Grammar: A Systematic Approach

Random reading and hoping to catch errors is not an editing strategy—it is optimism. Systematic grammar revision uses specific passes focused on specific error types, catching problems that holistic reading misses because the brain tends to read what it intended to write, not what is actually on the page. The revision process described here applies to essays, reports, and professional documents at any length.

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Frequently Asked Questions About Grammar Mistakes

Grammar as a Standard, Not a Barrier

Grammar rules exist to serve communication, not to provide grounds for excluding people whose language backgrounds differ from a narrow standard. The rules covered in this guide are worth knowing and applying not because violating them marks inferiority but because following them—particularly in formal academic and professional contexts—removes friction from the reader’s experience of your writing and keeps attention where it belongs: on your ideas.

The most useful frame for thinking about grammar in formal writing is pragmatic: what does this grammatical choice do for my reader? A comma splice does something real—it blurs the boundary between two thoughts and forces the reader to sort out the relationship the writer left unmarked. A dangling modifier does something real—it assigns an action to the wrong actor and, however briefly, creates an absurd or confusing image. A subject-verb disagreement does something real—it introduces a discordant note that interrupts the reading and briefly focuses attention on the sentence’s surface rather than its content.

Eliminating these errors is not about compliance with arbitrary rules. It is about respecting the reader’s attention and maintaining the contract that well-formed sentences represent: that the writer has thought carefully enough to control the language through which they are communicating. For writers who want systematic support developing that control—whether through editing, guidance, or model documents—our resources on developing writing skills through professional support and our proofreading and editing service provide practical pathways forward.