Grammar Mistakes That Make You Look Unprofessional (And How to Avoid Them)

The Email That Ruins Your Credibility

You send a proposal to a potential client.

Your idea is solid. Your pricing is competitive.

But you wrote: "We look forward to working with you're team."

And they think: "If they can't get basic grammar right, how can I trust them with my project?"

Fair? Maybe not. Reality? Absolutely.

Grammar mistakes signal carelessness. And carelessness costs you opportunities.

The Mistakes That Actually Matter

Not all grammar mistakes are equal.

Typo in casual Slack: Nobody cares Your/you're mistake in client proposal: Credibility destroyed

Know which errors matter in professional contexts.

Mistake #1: Your vs You're

Your = possession (your car, your idea) You're = you are (you're hired, you're right)

❌ "Looking forward to working with you're team" ✅ "Looking forward to working with your team"

❌ "Your going to love this" ✅ "You're going to love this"

Memory trick: If you can replace it with "you are," use "you're"

Mistake #2: Its vs It's

Its = possession (the dog wagged its tail) It's = it is (it's raining, it's Friday)

❌ "The company announced it's new product" ✅ "The company announced its new product"

❌ "Its been a great quarter" ✅ "It's been a great quarter"

Memory trick: If you can replace it with "it is," use "it's"

Mistake #3: Their vs They're vs There

Their = possession (their office, their team) They're = they are (they're coming, they're ready) There = location or existence (over there, there are three options)

❌ "There team is great" ✅ "Their team is great"

❌ "Their going to the meeting" ✅ "They're going to the meeting"

❌ "Put it over they're" ✅ "Put it over there"

Memory trick:

Their = possession (the "i" looks like a person)
They're = they are
There = here/there (both have "here")

Mistake #4: Affect vs Effect

Affect = verb (to influence) Effect = noun (the result)

❌ "How will this effect our timeline?" ✅ "How will this affect our timeline?"

❌ "What's the affect of the change?" ✅ "What's the effect of the change?"

Memory trick: Affect is an Action (verb), Effect is the End result (noun)

Exception: Effect can be a verb meaning "to bring about" (rare): "We will effect change"

Mistake #5: Then vs Than

Then = time (first this, then that) Than = comparison (better than, more than)

❌ "This option is better then that one" ✅ "This option is better than that one"

❌ "We'll launch, than we'll iterate" ✅ "We'll launch, then we'll iterate"

Mistake #6: Loose vs Lose

Loose = not tight (loose fit, loose interpretation) Lose = to misplace or fail to win (lose the game, lose your keys)

❌ "We can't afford to loose this client" ✅ "We can't afford to lose this client"

❌ "The bolts are lose" ✅ "The bolts are loose"

Mistake #7: Could of / Should of / Would of

Never write "could of"—it's not a thing.

❌ "I could of finished yesterday" ✅ "I could have finished yesterday" or "I could've finished yesterday"

Why this happens: "Could've" sounds like "could of" when spoken.

The rule: Could have, should have, would have (or their contractions)

Mistake #8: Me vs Myself

Myself is reflexive—only use it when you're doing something to yourself.

❌ "Send the report to John and myself" ✅ "Send the report to John and me"

❌ "Myself and Sarah will attend" ✅ "Sarah and I will attend"

✅ "I completed it myself" (reflexive—you did it to/by yourself)

Memory trick: Remove the other person. Would you say "Send the report to myself"? No. So use "me."

Mistake #9: Less vs Fewer

Fewer = countable things (fewer people, fewer errors) Less = uncountable things (less time, less money, less confusion)

❌ "We have less employees this year" ✅ "We have fewer employees this year"

❌ "This takes fewer time" ✅ "This takes less time"

Memory trick: If you can count it, use fewer.

Mistake #10: Who vs Whom

Who = subject (who is doing the action) Whom = object (receiving the action)

❌ "Whom is responsible?" ✅ "Who is responsible?" (who is the subject)

❌ "Who should I contact?" ✅ "Whom should I contact?" (whom is receiving the contact)

Memory trick: Replace with he/him. If "him" fits, use "whom." If "he" fits, use "who."

When Grammar Actually Matters

✅ Grammar Matters:

Client-facing communication
Job applications and resumes
Formal proposals
Published content (blogs, reports)
Executive communications
Anything that affects your professional image

⚠️ Grammar Matters Less:

Quick Slack messages to teammates
Internal brainstorming docs
Draft notes
Quick replies in fast-moving conversations

The rule: The more visible and formal, the more grammar matters.

Common Excuses (And Why They Don't Work)

"Everyone makes mistakes"

True, but:

Spell check catches most of these
One mistake = human, five mistakes = careless
Important communications deserve proofreading

"Grammar rules are classist/elitist"

Maybe, but:

Right or wrong, people judge you by your grammar
You can debate fairness after you get the job/client
Your choice: follow conventions or lose opportunities

"I'm not a writer, I'm a [engineer/designer/etc]"

Doesn't matter:

All professionals communicate in writing
Poor grammar undermines your technical expertise
Takes 30 seconds to proofread

How to Catch Your Mistakes

Strategy 1: Read It Out Loud

Your brain autocorrects when reading silently.

Read aloud: Mistakes jump out.

Strategy 2: Wait 10 Minutes

Write your email. Wait 10 minutes. Reread it.

Fresh eyes catch errors you missed.

Strategy 3: Use Tools

Grammarly, Hemingway, or built-in spell check.

Not perfect, but catches obvious errors.

Strategy 4: The Backwards Read

Read your email from bottom to top, sentence by sentence.

Why: Forces you to focus on each sentence independently.

The 4 Tests for Professional Writing

1. SIGNAL: Is my message clear despite any grammar?

Grammar matters, but clarity matters more.

2. OPPORTUNITY: Does this make me look competent?

Multiple errors = careless.

3. RISK: Is this important enough to proofread?

Client email? Proofread. Slack to teammate? Don't stress.

4. AFFECT: Would I trust someone who wrote this?

Be honest. Does this look professional?

Quick Reference Guide

MISTAKE	WRONG	RIGHT
Your/You're	"You're team"	"Your team"
Its/It's	"It's new product"	"Its new product"
Their/There/They're	"There team"	"Their team"
Affect/Effect	"Effect the timeline"	"Affect the timeline"
Then/Than	"Better then"	"Better than"
Loose/Lose	"Loose this client"	"Lose this client"
Could of	"Could of done it"	"Could have done it"
Me/Myself	"John and myself"	"John and I" (subject) or "John and me" (object)
Less/Fewer	"Less people"	"Fewer people"
Who/Whom	"Who should I call?"	"Whom should I call?"

Check Your Writing

Not sure if your grammar is correct?

Analyze your writing free with 4Angles →

Paste your text. See how it scores on:

SIGNAL (Is it clear?)
OPPORTUNITY (Does it look professional?)
RISK (Are there credibility-damaging errors?)
AFFECT (How will readers perceive this?)

No signup required. Just instant analysis.

The Email That Ruins Your Credibility

You send a proposal to a potential client.

Your idea is solid. Your pricing is competitive.

But you wrote: "We look forward to working with you're team."

And they think: "If they can't get basic grammar right, how can I trust them with my project?"

Fair? Maybe not. Reality? Absolutely.

Grammar mistakes signal carelessness. And carelessness costs you opportunities.

The Mistakes That Actually Matter

Not all grammar mistakes are equal.

Typo in casual Slack: Nobody cares Your/you're mistake in client proposal: Credibility destroyed

Know which errors matter in professional contexts.

Mistake #1: Your vs You're

Your = possession (your car, your idea) You're = you are (you're hired, you're right)

❌ "Looking forward to working with you're team" ✅ "Looking forward to working with your team"

❌ "Your going to love this" ✅ "You're going to love this"

Memory trick: If you can replace it with "you are," use "you're"

Mistake #2: Its vs It's

Its = possession (the dog wagged its tail) It's = it is (it's raining, it's Friday)

❌ "The company announced it's new product" ✅ "The company announced its new product"

❌ "Its been a great quarter" ✅ "It's been a great quarter"

Memory trick: If you can replace it with "it is," use "it's"

Mistake #3: Their vs They're vs There

Their = possession (their office, their team) They're = they are (they're coming, they're ready) There = location or existence (over there, there are three options)

❌ "There team is great" ✅ "Their team is great"

❌ "Their going to the meeting" ✅ "They're going to the meeting"

❌ "Put it over they're" ✅ "Put it over there"

Memory trick:

Their = possession (the "i" looks like a person)
They're = they are
There = here/there (both have "here")

Mistake #4: Affect vs Effect

Affect = verb (to influence) Effect = noun (the result)

❌ "How will this effect our timeline?" ✅ "How will this affect our timeline?"

❌ "What's the affect of the change?" ✅ "What's the effect of the change?"

Memory trick: Affect is an Action (verb), Effect is the End result (noun)

Exception: Effect can be a verb meaning "to bring about" (rare): "We will effect change"

Mistake #5: Then vs Than

Then = time (first this, then that) Than = comparison (better than, more than)

❌ "This option is better then that one" ✅ "This option is better than that one"

❌ "We'll launch, than we'll iterate" ✅ "We'll launch, then we'll iterate"

Mistake #6: Loose vs Lose

Loose = not tight (loose fit, loose interpretation) Lose = to misplace or fail to win (lose the game, lose your keys)

❌ "We can't afford to loose this client" ✅ "We can't afford to lose this client"

❌ "The bolts are lose" ✅ "The bolts are loose"

Mistake #7: Could of / Should of / Would of

Never write "could of"—it's not a thing.

❌ "I could of finished yesterday" ✅ "I could have finished yesterday" or "I could've finished yesterday"

Why this happens: "Could've" sounds like "could of" when spoken.

The rule: Could have, should have, would have (or their contractions)

Mistake #8: Me vs Myself

Myself is reflexive—only use it when you're doing something to yourself.

❌ "Send the report to John and myself" ✅ "Send the report to John and me"

❌ "Myself and Sarah will attend" ✅ "Sarah and I will attend"

✅ "I completed it myself" (reflexive—you did it to/by yourself)

Memory trick: Remove the other person. Would you say "Send the report to myself"? No. So use "me."

Mistake #9: Less vs Fewer

Fewer = countable things (fewer people, fewer errors) Less = uncountable things (less time, less money, less confusion)

❌ "We have less employees this year" ✅ "We have fewer employees this year"

❌ "This takes fewer time" ✅ "This takes less time"

Memory trick: If you can count it, use fewer.

Mistake #10: Who vs Whom

Who = subject (who is doing the action) Whom = object (receiving the action)

❌ "Whom is responsible?" ✅ "Who is responsible?" (who is the subject)

❌ "Who should I contact?" ✅ "Whom should I contact?" (whom is receiving the contact)

Memory trick: Replace with he/him. If "him" fits, use "whom." If "he" fits, use "who."

When Grammar Actually Matters

✅ Grammar Matters:

Client-facing communication
Job applications and resumes
Formal proposals
Published content (blogs, reports)
Executive communications
Anything that affects your professional image

⚠️ Grammar Matters Less:

Quick Slack messages to teammates
Internal brainstorming docs
Draft notes
Quick replies in fast-moving conversations

The rule: The more visible and formal, the more grammar matters.

Common Excuses (And Why They Don't Work)

"Everyone makes mistakes"

True, but:

Spell check catches most of these
One mistake = human, five mistakes = careless
Important communications deserve proofreading

"Grammar rules are classist/elitist"

Maybe, but:

Right or wrong, people judge you by your grammar
You can debate fairness after you get the job/client
Your choice: follow conventions or lose opportunities

"I'm not a writer, I'm a [engineer/designer/etc]"

Doesn't matter:

All professionals communicate in writing
Poor grammar undermines your technical expertise
Takes 30 seconds to proofread

How to Catch Your Mistakes

Strategy 1: Read It Out Loud

Your brain autocorrects when reading silently.

Read aloud: Mistakes jump out.

Strategy 2: Wait 10 Minutes

Write your email. Wait 10 minutes. Reread it.

Fresh eyes catch errors you missed.

Strategy 3: Use Tools

Grammarly, Hemingway, or built-in spell check.

Not perfect, but catches obvious errors.

Strategy 4: The Backwards Read

Read your email from bottom to top, sentence by sentence.

Why: Forces you to focus on each sentence independently.

The 4 Tests for Professional Writing

1. SIGNAL: Is my message clear despite any grammar?

Grammar matters, but clarity matters more.

2. OPPORTUNITY: Does this make me look competent?

Multiple errors = careless.

3. RISK: Is this important enough to proofread?

Client email? Proofread. Slack to teammate? Don't stress.

4. AFFECT: Would I trust someone who wrote this?

Be honest. Does this look professional?

Quick Reference Guide

MISTAKE	WRONG	RIGHT
Your/You're	"You're team"	"Your team"
Its/It's	"It's new product"	"Its new product"
Their/There/They're	"There team"	"Their team"
Affect/Effect	"Effect the timeline"	"Affect the timeline"
Then/Than	"Better then"	"Better than"
Loose/Lose	"Loose this client"	"Lose this client"
Could of	"Could of done it"	"Could have done it"
Me/Myself	"John and myself"	"John and I" (subject) or "John and me" (object)
Less/Fewer	"Less people"	"Fewer people"
Who/Whom	"Who should I call?"	"Whom should I call?"

Check Your Writing

Not sure if your grammar is correct?

Analyze your writing free with 4Angles →

Paste your text. See how it scores on:

SIGNAL (Is it clear?)
OPPORTUNITY (Does it look professional?)
RISK (Are there credibility-damaging errors?)
AFFECT (How will readers perceive this?)

No signup required. Just instant analysis.

Grammar Mistakes That Make You Look Unprofessional (And How to Avoid Them)

The Email That Ruins Your Credibility

The Mistakes That Actually Matter

Mistake #1: Your vs You're

Mistake #2: Its vs It's

Mistake #3: Their vs They're vs There

Mistake #4: Affect vs Effect

Mistake #5: Then vs Than

Mistake #6: Loose vs Lose

Mistake #7: Could of / Should of / Would of

Mistake #8: Me vs Myself

Mistake #9: Less vs Fewer

Mistake #10: Who vs Whom

When Grammar Actually Matters

✅ Grammar Matters:

⚠️ Grammar Matters Less:

Common Excuses (And Why They Don't Work)

"Everyone makes mistakes"

"Grammar rules are classist/elitist"

"I'm not a writer, I'm a [engineer/designer/etc]"

How to Catch Your Mistakes

Strategy 1: Read It Out Loud

Strategy 2: Wait 10 Minutes

Strategy 3: Use Tools

Strategy 4: The Backwards Read

The 4 Tests for Professional Writing

1. SIGNAL: Is my message clear despite any grammar?

2. OPPORTUNITY: Does this make me look competent?

3. RISK: Is this important enough to proofread?

4. AFFECT: Would I trust someone who wrote this?

Quick Reference Guide

Check Your Writing

Related Reading

Ready to Analyze Your Message?

Grammar Mistakes That Make You Look Unprofessional (And How to Avoid Them)

The Email That Ruins Your Credibility

The Mistakes That Actually Matter

Mistake #1: Your vs You're

Mistake #2: Its vs It's

Mistake #3: Their vs They're vs There

Mistake #4: Affect vs Effect

Mistake #5: Then vs Than

Mistake #6: Loose vs Lose

Mistake #7: Could of / Should of / Would of

Mistake #8: Me vs Myself

Mistake #9: Less vs Fewer

Mistake #10: Who vs Whom

When Grammar Actually Matters

✅ Grammar Matters:

⚠️ Grammar Matters Less:

Common Excuses (And Why They Don't Work)

"Everyone makes mistakes"

"Grammar rules are classist/elitist"

"I'm not a writer, I'm a [engineer/designer/etc]"

How to Catch Your Mistakes

Strategy 1: Read It Out Loud

Strategy 2: Wait 10 Minutes

Strategy 3: Use Tools

Strategy 4: The Backwards Read

The 4 Tests for Professional Writing

1. SIGNAL: Is my message clear despite any grammar?

2. OPPORTUNITY: Does this make me look competent?

3. RISK: Is this important enough to proofread?

4. AFFECT: Would I trust someone who wrote this?

Quick Reference Guide

Check Your Writing

Related Reading

Ready to Analyze Your Message?