Last week, I challenged myself to edit a friend’s manuscript without using any automated grammar checkers.

Just me, a red pen, and 300 pages of text.

By page fifty, I noticed something fascinating.

The errors that jumped out at me weren’t simple typos or missing commas.

They were subtle grammatical mistakes that most people would read right past without noticing.

This experience reminded me of research showing that only about 9% of native English speakers can consistently identify complex grammatical errors in everyday sentences.

The ability to spot these mistakes reveals something deeper about how our brains process language.

Today, I’m sharing nine sentences that will test your language processing abilities.

Each contains a grammatical error that might slip past even educated readers.

1) The first challenge

Here’s your first sentence: “Neither the manager or his assistant were available for comment.”

Did you catch it?

The error lies in the correlative conjunction.

When using “neither,” you must pair it with “nor,” not “or.”

The sentence should read: “Neither the manager nor his assistant was available for comment.”

There’s actually a second issue here too.

With “neither/nor” constructions, the verb should be singular (“was”) not plural (“were”).

This double error trips up many people because our brains often autocorrect as we read.

2) A sneaky subject-verb disagreement

Consider this sentence: “The team of researchers are presenting their findings tomorrow.”

Seems fine at first glance, right?

The error becomes clear when you identify the true subject.

“Team” is the subject, not “researchers.”

Since “team” is a collective noun treated as singular in American English, the verb should be “is” not “are.”

The correct version: “The team of researchers is presenting their findings tomorrow.”

This mistake is incredibly common because our brains focus on the word closest to the verb.

3) The dangling modifier trap

“Walking through the park, the flowers caught my attention.”

This sentence suggests the flowers were taking a stroll.

The opening phrase “Walking through the park” is a dangling modifier.

It doesn’t clearly connect to the subject performing the action.

The sentence should be restructured: “Walking through the park, I noticed the beautiful flowers.”

Now the person walking (I) immediately follows the modifier.

Research in cognitive linguistics shows that our brains often fill in these logical gaps automatically.

We understand what the writer meant, even when the grammar doesn’t support it.

4) Pronoun confusion

“Everyone should bring their laptop to the meeting.”

This seems perfectly natural in everyday speech.

But grammatically, “everyone” is singular while “their” is plural.

Traditional grammar rules would require: “Everyone should bring his or her laptop to the meeting.”

I’ll admit this one is evolving.

Many style guides now accept singular “they” to avoid awkward constructions.

Still, recognizing the traditional error shows sharp grammatical awareness.

5) The comparison problem

Here’s a sentence I see everywhere: “This coffee is more stronger than yesterday’s brew.”

The error? Double comparison.

You can use either “more strong” or “stronger,” but not both.

The correct version is simply: “This coffee is stronger than yesterday’s brew.”

Our brains often skip over these redundancies because we’re focused on meaning rather than structure.

• This same error appears with words like “more better”
• It happens with “most fastest”
• And with “more quieter”
• The pattern is always the same: redundant comparison markers

6) Misplaced apostrophes

“The company announced it’s new policy regarding remote work.”

This might be the most common error in written English today.

“It’s” means “it is” or “it has.”

For possession, you need “its” without the apostrophe.

The sentence should read: “The company announced its new policy regarding remote work.”

When I first started paying attention to my writing, this error haunted my drafts.

Even now, I sometimes catch myself making it when typing quickly.

7) The split infinitive debate

“She decided to quickly review the documents before the meeting.”

Technically, this splits the infinitive “to review” with the adverb “quickly.”

Traditional grammarians would prefer: “She decided to review the documents quickly before the meeting.”

Or: “She decided quickly to review the documents before the meeting.”

Modern usage has largely accepted split infinitives, especially when they sound more natural.

But recognizing them still demonstrates advanced grammatical knowledge.

8) Subjunctive mood mistakes

“If I was rich, I would travel the world.”

This sentence needs the subjunctive mood.

When expressing hypothetical or contrary-to-fact conditions, use “were” instead of “was.”

The correct version: “If I were rich, I would travel the world.”

The subjunctive is dying in casual English.

Most people wouldn’t notice this error in conversation.

But in formal writing, it still matters.

9) The who/whom distinction

“The person who you called yesterday returned your message.”

This final challenge tests your understanding of case.

“Who” is for subjects; “whom” is for objects.

Since “you” is the subject doing the calling, and the person is receiving the action, we need “whom.”

The correct sentence: “The person whom you called yesterday returned your message.”

I spent years avoiding “whom” entirely because I wasn’t confident about when to use it.

Now I use this simple trick: if you can substitute “him” or “her,” use “whom.”

If “he” or “she” works, use “who.”

Final thoughts

How many errors did you catch before reading the explanations?

If you identified seven or more, your grammatical processing truly is exceptional.

These aren’t just arbitrary rules.

Understanding these patterns reveals how deeply you process language structure, not just meaning.

The fascinating part is that strong grammar recognition correlates with other cognitive abilities like pattern recognition, logical thinking, and even mathematical reasoning.

Your brain isn’t just memorizing rules.

It’s recognizing complex patterns and applying them in real-time.

Keep challenging yourself with difficult texts.

Notice the grammar choices skilled writers make.

Question constructions that sound slightly off.

Your language processing abilities are like muscles that strengthen with use.

What sentence constructions do you find yourself questioning most often?