Common English Grammar Mistakes and How to Avoid Them: A Complete Guide

Grammar mistakes happen to everyone. Even seasoned writers, professional editors, and English teachers occasionally slip up on the tricky rules that govern our language. The difference between good writers and great ones isn’t perfection—it’s awareness, understanding, and the ability to catch and correct errors before they undermine your message.

English grammar presents unique challenges. Unlike many languages with consistent rules, English is riddled with exceptions, irregular patterns, and contradictions that developed over centuries of linguistic evolution. Words that sound identical have completely different meanings. Rules that apply in one context fail in another. And perhaps most frustrating, many “rules” you learned in school aren’t actually rules at all—they’re stylistic preferences that have taken on the weight of law.

This comprehensive guide explores the most common English grammar mistakes, explains why they happen, and provides practical strategies to avoid them. Whether you’re crafting professional emails, writing academic papers, creating content for your business, or simply want to communicate more effectively, understanding these common pitfalls will strengthen your writing and boost your confidence.

Why Grammar Matters More Than You Think

Before diving into specific mistakes, let’s address the fundamental question: does grammar really matter in modern communication?

The short answer is yes—but perhaps not in the way you expect. Perfect grammar isn’t about sounding pretentious or following arbitrary rules. It’s about clarity, credibility, and respect for your reader. When your grammar is solid, your ideas shine through without distraction. When it’s shaky, readers focus on the errors instead of your message.

In professional contexts, grammar mistakes can cost you opportunities. Research shows that hiring managers frequently dismiss applications with grammar errors, even for positions where writing isn’t the primary responsibility. In business communications, poor grammar can damage your credibility and make your organization seem less professional. Online, grammar mistakes can reduce engagement, hurt your SEO performance, and diminish your authority on a subject.

But beyond professional consequences, good grammar simply makes communication easier. It reduces ambiguity, prevents misunderstandings, and allows you to express complex ideas precisely. That’s why mastering common grammar mistakes is worth the effort.

The Most Common Grammar Mistakes (and How to Fix Them)

Confusing “There,” “Their,” and “They’re”

This trio of homophones—words that sound identical but have different meanings—trips up even experienced writers. The confusion stems from their pronunciation: all three sound exactly the same in spoken English, so your ear provides no help in distinguishing them.

Understanding each word:

There indicates location or existence. Use it to point to a place (“Put your bag over there”) or to introduce the existence of something (“There are three reasons why this matters”).

Their shows possession or ownership. It’s a possessive pronoun indicating that something belongs to a group of people (“Their house is beautiful” or “The students submitted their assignments”).

They’re is a contraction—a shortened form of “they are.” Contractions combine two words by replacing letters with an apostrophe (“They’re arriving at noon” means “They are arriving at noon”).

How to avoid this mistake:

The most reliable method is substitution testing. When you’ve written one of these words, try replacing it with “they are.” If the sentence still makes sense with “they are,” then “they’re” is correct. If not, move to the next test.

If the word indicates ownership, use “their.” Ask yourself: does this show that something belongs to them? If yes, “their” is your answer.

If neither substitution works, “there” is almost certainly correct.

Consider these examples:

• “They’re going to their house over there.” (They are going / possessive / location)
• “There is no doubt that their performance exceeded expectations.” (Existence / possessive)
• “If they’re willing to invest their time, there will be results.” (They are / possessive / existence)

Mixing Up “Your” and “You’re”

Similar to the there/their/they’re confusion, the your/you’re mistake results from homophones that sound identical but serve different grammatical functions.

Your is a possessive adjective indicating ownership: “your car,” “your idea,” “your responsibility.” It answers the question “whose?”

You’re contracts “you are” into a single word: “You’re talented” (You are talented), “You’re making progress” (You are making progress).

How to avoid this mistake:

Apply the same substitution test used for they’re. Read your sentence aloud and replace the word with “you are.” If it sounds right, use “you’re.” If it sounds awkward or wrong, use “your.”

Examples:

• “Your approach to problem-solving is creative.” (Possessive—the approach belongs to you)
• “You’re demonstrating excellent judgment.” (You are demonstrating)
• “If you’re not careful, your reputation could suffer.” (You are / possessive)

This mistake often appears in rushed writing or casual digital communication. Taking an extra second to mentally say “you are” can eliminate this error from your writing entirely.

Misusing Apostrophes

Apostrophe confusion causes some of the most visible grammar mistakes in published writing—from storefront signs to social media posts. The rules governing apostrophes aren’t actually complicated, but they’re frequently misunderstood.

Apostrophes have exactly two legitimate uses in standard English:

1. Forming possessives to show ownership:

• Singular nouns: Add ‘s (“the dog’s collar,” “James’s book,” “the company’s policy”)
• Plural nouns ending in s: Add only an apostrophe (“the teachers’ lounge,” “the students’ projects”)
• Plural nouns not ending in s: Add ‘s (“the children’s toys,” “the women’s conference”)

2. Creating contractions by replacing omitted letters:

• it’s = it is or it has
• don’t = do not
• won’t = will not
• they’ve = they have

What apostrophes DON’T do:

Apostrophes do not create plurals. This mistake appears everywhere: “Apple’s for sale” (wrong—should be “Apples for sale”), “The 1990’s were great” (wrong—should be “The 1990s”).

The its/it’s confusion deserves special attention because it contradicts the normal possessive rule. Remember: “it’s” always means “it is” or “it has.” The possessive form is “its” with no apostrophe (“The dog wagged its tail”). This exception exists because possessive pronouns (his, hers, its, ours, theirs) never use apostrophes.

Examples:

• Correct: “The company updated its website.”
• Incorrect: “The company updated it’s website.”

Subject-Verb Agreement Errors

Subject-verb agreement means your verb must match your subject in number—singular subjects take singular verbs, plural subjects take plural verbs. This sounds simple, but several factors complicate it in practice.

The main challenge arises when prepositional phrases separate the subject from its verb. Writers sometimes match the verb to the nearest noun rather than the actual subject.

Incorrect: “The collection of paintings are impressive.” Correct: “The collection of paintings is impressive.”

The subject is “collection” (singular), not “paintings” (plural). The prepositional phrase “of paintings” is just a modifier.

Common agreement troublemakers:

Collective nouns (team, committee, family, group) usually take singular verbs in American English when referring to the unit as a whole: “The team is winning” (the team as a single unit). However, when emphasizing individual members, plural verbs work: “The team are arguing among themselves” (individual team members).

Compound subjects joined by “and” typically take plural verbs: “The CEO and CFO are attending.” But subjects joined by “or” or “nor” match the verb to the closest noun: “Neither the manager nor the employees are happy” (plural verb because “employees” is plural and closest).

Indefinite pronouns like “everyone,” “everybody,” “anyone,” “someone,” “nobody,” and “each” are grammatically singular despite feeling plural: “Everyone is welcome” (not “everyone are”).

How to avoid this mistake:

Mentally cross out prepositional phrases and modifiers to identify the true subject. Then match your verb to that subject alone, ignoring everything else between them.

Run-On Sentences

A run-on sentence improperly joins two or more independent clauses (complete thoughts that could stand alone as sentences) without appropriate punctuation or connecting words. Run-ons create confusion by cramming too much information together without showing readers where one idea ends and another begins.

Types of run-on sentences:

Fused sentences smash independent clauses together with no punctuation: “I love writing it helps me think clearly about complex problems.”

Comma splices incorrectly use only a comma to join independent clauses: “The meeting ran late, we missed dinner.”

How to fix run-on sentences:

You have several options, depending on the relationship between your clauses:

1. Use a period to create separate sentences: “I love writing. It helps me think clearly.”

2. Use a semicolon when clauses are closely related: “I love writing; it helps me think clearly.”

3. Use a comma plus a coordinating conjunction (and, but, or, nor, for, so, yet): “I love writing, for it helps me think clearly.”

4. Use a subordinating conjunction to show how ideas relate: “I love writing because it helps me think clearly.”

5. Use a dash or colon when appropriate: “I love writing—it helps me organize complex thoughts.”

The best choice depends on how your ideas relate. If they’re equally important and closely connected, a semicolon works well. If one idea causes or explains another, subordinating conjunctions (because, although, while, since) clarify that relationship.

Sentence Fragments

While run-ons pack too much into one sentence, fragments lack something essential—either a subject, a verb, or a complete thought. Fragments leave readers hanging, waiting for information that never arrives.

Common types of fragments:

Dependent clause fragments begin with subordinating words but lack an independent clause: Fragment: “Because I was late.” Complete: “I missed the bus because I was late.”

Participle phrase fragments start with -ing or -ed verbs but lack a subject or auxiliary verb: Fragment: “Running through the park every morning.” Complete: “Running through the park every morning keeps me energized.”

Infinitive phrase fragments begin with “to” plus a verb: Fragment: “To improve your writing skills.” Complete: “To improve your writing skills, practice daily.”

When fragments work:

Intentional fragments can create emphasis or match conversational tone in creative writing: “Will she succeed? Absolutely.” In formal writing, however, avoid fragments unless you’re deliberately using them for stylistic effect and can explain why.

How to avoid unintentional fragments:

After writing each sentence, ask: Does this express a complete thought? Could this stand alone and make sense? Does it have both a subject and a verb? If you answer “no” to any question, you’ve likely written a fragment.

Overusing Passive Voice

Passive voice constructions make the recipient of an action the grammatical subject, often obscuring who performed the action. While passive voice has legitimate uses, overusing it weakens writing and reduces clarity.

Active voice: The subject performs the action. “The committee approved the proposal.”

Passive voice: The subject receives the action. “The proposal was approved by the committee.”

Why passive voice creates problems:

It’s often wordier: Passive constructions typically require more words to express the same idea.

It can be vague: Passive voice allows writers to avoid stating who performed an action: “Mistakes were made” (by whom?).

It reduces energy and directness: Active voice creates more dynamic, engaging prose.

When passive voice is appropriate:

Use passive voice when:

• The actor is unknown: “The window was broken sometime last night.”
• The actor is irrelevant: “Rice is grown in many regions.”
• You want to emphasize the recipient: “The victim was taken to the hospital.”
• Scientific writing requires objectivity: “The mixture was heated to 100°C.”

How to identify and fix passive voice:

Look for forms of “to be” (is, was, were, been) plus a past participle (a verb typically ending in -ed). Ask yourself: Who’s doing what? Then restructure to make the actor the subject.

Passive: “The report was written by Sarah.” Active: “Sarah wrote the report.”

Incorrect Comma Placement

Commas cause more confusion than perhaps any other punctuation mark. They serve multiple functions, follow numerous rules, and allow some subjective judgment. Despite this complexity, understanding a few key principles eliminates most comma errors.

Essential comma rules:

After introductory elements: Place a comma after introductory words, phrases, or clauses that come before the main sentence: “After finishing my coffee, I started working.” “However, we need to reconsider.” “When you arrive, please call me.”

Between independent clauses joined by coordinating conjunctions: Use a comma before “and,” “but,” “or,” “nor,” “for,” “so,” or “yet” when connecting complete sentences: “I wanted to attend, but I had a conflict.”

To set off non-essential elements: Use commas to surround information that could be removed without changing the sentence’s basic meaning: “My neighbor, who works in finance, offered to help.”

Without commas: “The neighbor who plays loud music is moving.” (This specifies which neighbor—essential information.)

In lists: Use commas to separate three or more items. The Oxford comma (the comma before “and” in a list) is optional but recommended for clarity: “We need bread, milk, and eggs.”

Common comma mistakes to avoid:

Comma splices: Don’t use only a comma to join independent clauses (as discussed in the run-on section).

Commas between subjects and verbs: Don’t separate a subject from its verb with a comma: Incorrect: “The tall man in the blue shirt, is my brother.” Correct: “The tall man in the blue shirt is my brother.”

How to improve comma usage:

Read your sentences aloud. Your natural speaking rhythm often indicates where commas belong—they typically appear where you’d pause slightly in speech. However, don’t rely solely on this method; learn the actual rules for proper placement.

Misusing “Fewer” and “Less”

This distinction seems minor but significantly affects precision in professional and formal writing. The rule is straightforward: “fewer” goes with countable items, “less” with uncountable quantities.

Fewer modifies plural nouns—things you can count individually:

• “fewer apples” (you can count: 1 apple, 2 apples)
• “fewer students” (you can count students)
• “fewer mistakes” (you can count mistakes)

Less modifies singular or mass nouns—things measured as wholes or quantities:

• “less water” (you can’t count water; you measure it)
• “less traffic” (traffic is a collective whole)
• “less confusion” (you can’t count confusion)

The grocery store test:

If you’ve seen grocery store signs reading “10 items or less,” you’ve witnessed this error in action. It should be “10 items or fewer” because items are countable. The incorrect “less” appears so commonly that it sounds natural to many people, but “fewer” is grammatically correct.

How to choose correctly:

Ask yourself: Can I count this thing individually? If yes, use “fewer.” If it’s measured as a whole or quantity, use “less.”

More examples:

• “Fewer people attended this year.” (countable people)
• “We had less time than expected.” (uncountable quantity)
• “The revised version has fewer errors and less ambiguity.” (countable errors, uncountable ambiguity)

Dangling Modifiers

Dangling modifiers are phrases that don’t clearly modify any word in the sentence, creating unintentionally humorous or confusing meanings. They typically occur when a modifying phrase begins a sentence but the actual subject appears too late or not at all.

The problem occurs because modifying phrases at the beginning of sentences should describe the subject of the main clause. When they don’t, the modifier “dangles” without a clear connection.

Classic examples:

Incorrect: “Walking down the street, the trees looked beautiful.” (This sentence says the trees were walking.)

Incorrect: “After rotting in the cellar for weeks, my brother brought up some oranges.” (This suggests the brother was rotting, not the oranges.)

Incorrect: “While typing the report, the computer suddenly crashed.” (The computer wasn’t doing the typing.)

How to fix dangling modifiers:

Make sure the subject immediately following the introductory phrase is actually performing the action described:

Correct: “Walking down the street, I noticed the beautiful trees.”

Correct: “After the oranges had rotted in the cellar for weeks, my brother brought them up.”

Correct: “While I was typing the report, the computer suddenly crashed.”

Alternatively, you can revise the modifying phrase itself to include the subject:

Correct: “As I walked down the street, the trees looked beautiful.”

How to spot dangling modifiers in your writing:

When you begin a sentence with a phrase ending in -ing or -ed, immediately check: Does the noun following the comma actually perform the action in the opening phrase? If not, you have a dangling modifier.

Using Double Negatives

Double negatives occur when two negative words appear in the same clause, typically creating the opposite of the intended meaning—or at least causing confusion.

In standard English, two negatives mathematically cancel each other out:

“I don’t have nothing” technically means “I do have something” (don’t + nothing = something).

The speaker usually means: “I don’t have anything” or “I have nothing.”

Common double negative constructions:

• “I don’t need no help” → “I don’t need any help”
• “She doesn’t know nothing” → “She doesn’t know anything”
• “We can’t find it nowhere” → “We can’t find it anywhere”
• “He doesn’t never call” → “He never calls” or “He doesn’t ever call”

Why double negatives persist:

In some English dialects and many other languages, double negatives are grammatically standard and simply reinforce the negative meaning. However, in standard written English, they’re considered incorrect.

Intentional double negatives for emphasis:

Literary writing sometimes uses double negatives deliberately for understatement or irony: “That’s not unimportant” suggests something is actually quite important, but more subtly than saying “That’s important.”

How to avoid accidental double negatives:

When you write a negative word (no, not, never, nothing, nobody), scan the rest of your clause for other negatives. Use only one negative per statement, or restructure your sentence.

Confusing “Then” and “Than”

Despite looking similar, “then” and “than” serve completely different grammatical functions, and confusing them creates obvious errors.

Then relates to time—it indicates sequence, timing, or consequence:

• “First we’ll eat, then we’ll watch the movie.” (sequence)
• “The meeting starts at noon; I’ll see you then.” (specific time)
• “If you finish early, then you can leave.” (consequence)

Than is used in comparisons—it shows how one thing relates to another:

• “She is taller than her brother.” (comparing heights)
• “This solution is better than the alternative.” (comparing quality)
• “I’d rather walk than drive.” (comparing preferences)

How to remember the difference:

Think of “than” containing the letter “a” for “add comparison”—you’re adding something to compare against.

Think of “then” containing the letter “e” for “when”—it’s about time.

Or remember this simple phrase: “First this, then that, than comparing.”

Examples in context:

• “I finished my work, then went home, and realized I’d accomplished more than expected.” (Then = time sequence; than = comparison)

Beyond Individual Mistakes: Developing Grammar Intuition

Learning these specific rules helps, but the most effective path to better grammar involves developing intuition—an automatic sense of what sounds right. This intuition comes from exposure to well-written text and conscious attention to language patterns.

Read Actively and Extensively

Reading quality writing is perhaps the most powerful grammar improvement strategy. When you read professionally edited books, reputable publications, and well-crafted articles, you unconsciously absorb correct grammar patterns. Your brain starts recognizing what “looks right” without consciously applying rules.

Make your reading active rather than passive:

• Notice sentence structures that flow particularly well
• Observe how professional writers handle punctuation
• Pay attention to paragraph transitions and organization
• Study how skilled writers vary sentence length and structure

The more you read, the more naturally correct grammar patterns embed themselves in your writing instincts. Quality reading materials improve writing skills in ways that studying rules alone cannot achieve.

Learn from Your Own Mistakes

Every grammar mistake you make represents a learning opportunity. Rather than feeling embarrassed when someone corrects you or when you notice an error in your published work, treat it as valuable feedback.

Keep a personal error log:

• Track which mistakes you make repeatedly
• Write down the correct form alongside your error
• Review this log periodically to reinforce correct usage

Patterns will emerge. Perhaps you consistently confuse affect/effect, or you habitually create comma splices. Once you identify your personal weak points, you can focus improvement efforts where they’ll have the greatest impact.

Use Grammar Tools Wisely

Grammar checking software like Grammarly, ProWritingAid, or even your word processor’s built-in checker can catch many errors. However, these tools have significant limitations:

They miss context-dependent errors (using “there” instead of “their” when both are grammatically valid in the sentence structure).

They sometimes flag correct constructions as errors based on overly rigid rules.

They can’t evaluate whether your tone, style, or word choice suits your audience and purpose.

Best practice: Use grammar checkers as a safety net, not a crutch. Write first without relying on them, then use them to catch errors you missed. When the software flags something, don’t blindly accept its suggestion—understand why it’s suggesting a change and whether that change actually improves your writing.

Practice Deliberate Writing

Improvement requires more than just writing frequently—it requires deliberate practice, where you consciously focus on specific aspects of grammar as you write.

Choose one or two grammar concepts to focus on during each writing session:

• “Today I’ll pay special attention to subject-verb agreement.”
• “In this piece, I’ll watch for passive voice constructions.”
• “I’ll carefully consider each comma placement in this email.”

This focused attention helps you internalize rules more quickly than trying to remember everything at once. Over time, these deliberate practices become automatic habits.

Write Out Loud

Reading your writing aloud engages different mental processes than silently reading. When you speak your words, you’ll often hear awkward constructions, missing words, or unclear passages that looked fine on the page. Your ear catches rhythm problems, run-on sentences, and unnatural phrasing.

This technique is particularly valuable for catching:

• Sentences that are too long or complex
• Missing transitions between ideas
• Repetitive word choices
• Grammatical errors that “sound wrong” even if you can’t immediately identify the rule violation

Grammar in Different Contexts

Grammar rules aren’t absolute—appropriate usage depends on context, audience, and purpose. Understanding when to apply strict rules versus when to adopt a more flexible approach demonstrates true language mastery.

Formal Writing Contexts

Academic papers, business proposals, professional reports, and legal documents require adherence to standard grammar rules. In these contexts:

• Avoid contractions (use “do not” rather than “don’t”)
• Minimize passive voice unless scientifically appropriate
• Follow all conventional punctuation rules
• Eliminate colloquialisms and casual language
• Use complete sentences without intentional fragments

Mistakes in formal writing carry greater consequences because readers expect precision and professionalism. These documents often influence important decisions, so clarity and correctness matter significantly.

Professional Communication

Emails, business letters, presentations, and workplace documentation occupy a middle ground. They should be correct but can be less rigid than academic writing:

• Contractions are generally acceptable
• A conversational tone often works well
• Minor stylistic variations are tolerable
• Clarity and efficiency matter more than perfect adherence to every rule

However, audience matters. An email to your company’s CEO likely requires more formality than one to a peer.

Creative and Casual Writing

Personal blogs, social media, creative fiction, and informal correspondence allow the most flexibility:

• Intentional fragments can create emphasis
• Casual language and contractions are expected
• Bending grammar rules for stylistic effect is acceptable
• Matching your audience’s communication style matters more than perfect grammar

Even in creative contexts, effective communication requires underlying grammar knowledge. You need to know the rules to break them effectively. Random errors look unprofessional; intentional rule-breaking for effect demonstrates mastery.

The Psychology of Grammar Mistakes

Understanding why we make grammar mistakes helps us prevent them more effectively.

Interference from Speech Patterns

We learn spoken language first, and speech operates by different rules than written language. In conversation, homophones cause no confusion—context makes meaning clear. When we write, we sometimes transcribe our speech directly, importing errors that don’t exist in spoken form (confusing there/their/they’re, for example).

Cognitive Load and Attention

Writing requires managing multiple demands simultaneously: generating ideas, organizing thoughts, choosing words, constructing sentences, and applying grammar rules. When cognitive load is high, grammar often suffers. This is why first drafts contain more errors than revised versions—you’re focused on getting ideas down, not perfecting every sentence.

Solution: Separate drafting from editing. During initial writing, focus on content and flow. Return later to address grammar specifically when you can give it full attention.

The Curse of Knowledge

Once you understand a concept, imagining what it’s like not to understand becomes difficult. You know what you meant to write, so your brain sometimes “sees” correct grammar even when errors exist on the page. This is why having someone else review important writing helps—fresh eyes catch mistakes you’ve become blind to.

Building Long-Term Grammar Skills

Improving grammar isn’t a one-time project—it’s an ongoing process of learning, practice, and refinement.

Set realistic expectations: Even professional writers and editors make grammar mistakes. The goal isn’t perfection; it’s consistent improvement and awareness.

Focus on high-impact errors first: Some mistakes (like using “your” instead of “you’re” in professional communication) create worse impressions than others. Prioritize fixing the errors that most affect how others perceive your writing.

Develop editing habits: Build review time into your writing process. Before sending important emails or publishing content, step away for a few minutes then return with fresh eyes.

Seek feedback: Ask colleagues, friends, or mentors to point out recurring errors in your writing. External feedback provides insights self-review might miss.

Study grammar systematically: Rather than randomly learning rules, work through a comprehensive grammar guide or take a structured course. Understanding the logic behind grammar rules makes them easier to remember and apply.

Celebrate progress: Notice when you catch an error you previously missed or when a particular rule becomes automatic. Improvement happens gradually, and recognizing progress maintains motivation.

Final Thoughts: Grammar as a Tool for Clearer Thinking

Grammar serves a deeper purpose than avoiding embarrassment or impressing others. The process of constructing grammatically correct sentences clarifies your thinking. When you struggle to write something grammatically, it often reveals unclear thinking about the underlying ideas.

Wrestling with subject-verb agreement forces you to clarify what you’re actually talking about—what is your true subject? Eliminating run-on sentences requires identifying distinct ideas and deciding how they relate. Fixing dangling modifiers demands precision about who’s doing what.

Every grammar rule, despite seeming arbitrary, exists to reduce ambiguity and increase precision. English might have complex grammar, but this complexity allows for subtle distinctions in meaning that simpler systems can’t capture.

As you work to avoid common grammar mistakes, remember that grammar is a tool, not a weapon. Its purpose is helping you communicate more effectively, not judging others or feeling superior. Everyone makes grammar mistakes, and the goal is simply making fewer of them over time while maintaining your unique voice and style.

With awareness of these common errors, strategies for avoiding them, and commitment to ongoing improvement, you can make grammar your ally rather than your adversary. Clear grammar leads to clear communication—and clear communication leads to being better understood, more respected, and more effective in every area of life where writing matters.