Common Grammar Mistakes in English and How to Avoid Them
Grammar errors in English range from the trivially cosmetic to the kind that genuinely change meaning — sometimes in ways the writer would prefer not to discover after the fact. This page covers the most persistent grammar mistakes encountered in American English writing and speech, explains the underlying rules that make them mistakes, and draws clear lines between errors that matter and those that mostly just attract red ink from grammar enthusiasts. The framework draws on guidance from the Modern Language Association, The Chicago Manual of Style, and Merriam-Webster's published usage notes.
Definition and Scope
A grammar mistake is a deviation from the established structural rules of a language — rules governing how words combine to form meaningful, correctly interpreted sentences. That definition sounds airtight until you realize English has at least 3 distinct layers of "correct": formal written standard (academic and legal prose), standard edited American English (journalism, business), and spoken informal registers that operate by their own stable logic.
The English Grammar Fundamentals framework distinguishes between prescriptive rules (what authorities say should be done) and descriptive rules (what fluent speakers actually do). Most practical grammar instruction sits somewhere between the two. The errors covered here are the ones that The Chicago Manual of Style (17th edition) and the American Psychological Association's Publication Manual (7th edition) both flag as genuine barriers to clarity — not just shibboleths.
How It Works
Grammar mistakes cluster into recognizable categories. The most common fall into 4 types:
- Agreement errors — mismatches between subject and verb, or pronoun and antecedent
- Case errors — using the wrong form of a pronoun (nominative vs. objective)
- Punctuation-driven errors — the comma splice, the fused sentence, the misplaced apostrophe
- Word choice errors — confusing words that sound similar but function differently (homophones and near-homophones)
Each type has its own failure mechanism. Agreement errors typically trace to a writer losing track of the grammatical subject — a problem that multiplies when prepositional phrases or relative clauses intervene between subject and verb. "The quality of the arguments are impressive" fails because "quality," not "arguments," is the subject; The Chicago Manual of Style (§5.138) treats this as a standard subject-verb agreement violation.
Case errors are rampant with compound constructions. "Between you and I" is grammatically incorrect — "between" is a preposition and takes objective-case pronouns, making "between you and me" the correct form. Merriam-Webster's usage note on "I vs. me" confirms that hypercorrection (reaching for "I" because it sounds formal) drives this error more than ignorance of pronoun function.
Comma splices join two independent clauses with only a comma: "The report was finished, the team celebrated." The fix is a period, a semicolon, or a coordinating conjunction. Fused sentences omit even the comma. Both errors are covered in detail at English Punctuation Rules.
Common Scenarios
Subject-verb agreement with collective nouns. "The committee has decided" (treating committee as a unit) and "the committee have submitted their individual reports" (treating members as individuals) are both defensible depending on context — but mixing both within a document causes inconsistency. The AP Stylebook recommends treating collective nouns as singular in American English.
"Who" vs. "whom." The distinction maps cleanly onto pronoun case: "who" is nominative (acts as a subject), "whom" is objective (acts as an object). The substitution test is reliable — replace "who/whom" with "he/him." If "him" sounds right, "whom" is correct. If "he" sounds right, "who" is correct. "Who called?" = "He called." "Whom did she call?" = "She called him."
Misplaced and dangling modifiers. "Running down the street, the trees looked beautiful" dangles because the trees are not running. The modifier must attach to the noun it actually describes. This error type is one of the most visually striking in formal writing — the English Sentence Structure reference covers placement rules systematically.
Its vs. it's. "It's" is a contraction of "it is" or "it has." "Its" is the possessive pronoun. The apostrophe signals contraction, not possession — a counterintuitive rule that trips up even careful writers. Merriam-Webster's online dictionary flags this as one of the most frequently confused pairs in American English.
For homophones and near-homophones more broadly — affect/effect, further/farther, lay/lie — English Homophones and Commonly Confused Words provides a structured reference.
Decision Boundaries
Not every deviation from a prescriptive rule constitutes an error. The split infinitive ("to boldly go") was condemned by 19th-century grammarians but is widely accepted in standard edited American English — The Chicago Manual of Style (§5.108) explicitly states that split infinitives are not inherently wrong. Similarly, ending a sentence with a preposition, once a classroom prohibition, is standard usage when the alternative would produce stilted prose.
The useful decision boundary: does the deviation impair clarity, change meaning, or signal carelessness to a specific audience? An academic paper submitted to a peer-reviewed journal operates under tighter constraints than a business email. Legal and professional contexts — explored further at English in Professional and Legal Contexts and across the englishlanguageauthority.com reference network — carry their own precision standards where agreement errors and ambiguous pronoun reference can have real consequences.
The 3-question diagnostic is serviceable: Does it change what the sentence means? Does it violate a rule the target audience will recognize and expect? Would a professional editor flag it? If the answer to all 3 is no, the "error" may be a style preference, not a grammar failure.