paper with editing marks

7 Grammatical Errors You May Not Realize You’re Making

Face it, we all do it. We leave out the apostrophe, we use “effect” when we mean “affect,” and sometimes we even—gasp!—change the verb tense. It all adds up to loss of respect in the professional world and lower grades in academia. So to help you stop the madness, here are seven of the most common grammatical errors both students and professionals make. Hopefully after reading this, your writing will be better than ever!

1. Verb Conjugation

Did you know that we conjugate verbs in English just like in the foreign languages we study? If you have ever changed the Spanish verb “estar” (to be) into “yo estoy,” “tu estas,” and “nosotros estamos,” then you know how to conjugate a verb.

In English, there really are only two verb endings: the verb itself without any change, or adding “s.”

Check it out:

  • I love

  • you love

  • he/she/it loves

  • we love

  • they love

And even though we have irregular endings just like most foreign languages (I am, you are, he/she/it is), there are still only about two changes to the verb. Verb conjugation becomes important when you’re dealing with subject-verb agreement.

2. Making Verbs Agree with Subjects

Speaking of such, let’s talk about this subject-verb thing. What does it mean for a subject and verb to agree? It’s all about the subject. It’s really not that difficult of a concept. You may have seen mistakes like “they loves” or “you is” in writing before. That’s subject-verb agreement at its worst.

The simple rule is this:

Singular subject = “s” on the verb (“he loves” or “he has”)

Plural subject = no “s” on the verb (“they love” or “we have”)

Remember that rule, and your subjects and verbs will always agree—no matter what you’re writing.

Keep in mind that I’ve simplified this rule to help beginning writers. For example, I haven’t discussed what to do with singular subjects “I” and “you,” which are conjugated without the “s,” just like we do for plural subjects.

3. Maintaining the Same Tense

One of the most basic issues in writing is the verb tense. Should you use past or present or conditional or future tense? And once you choose a tense, can you switch to another one?

Most of the grammatical errors we’ve talked about so far are based on present tense verb endings. In English, they are even easier than other tenses.

In past tense, just add -d to the verb for every I, you, he/she/it, or they (except “to be,” which becomes “was” or “were” in past tense). In the conditional or future tenses, all you’re doing is adding a word in front of the verb: I could be; I will be.

For example:

  • Present tense: I jump

  • Past tense: I jumped

  • Conditional or future tense: I will jump / I could jump

But maintaining the same tense throughout any piece of writing is very important. When you start a sentence, keep the verb tense the same for every verb (this is also called parallel structure—when all verb endings match). In other words, if you begin in present tense, make sure all your verbs are in present tense.

Keep in mind that the most common tense for most writing is past tense. So if you pick past tense, don’t change your sentence, paragraph, or essay to conditional or present tense unless it’s clearly needed.

For example:

Do Not

Lilly the cat jumped up onto the windowsill and will go back into the house. It’s warm and the smell of fish is in the air. It will make her hungry.

The paragraph started with past tense, but incorrectly used future and present tense later on.


Lilly the cat jumped up onto the windowsill and went back into the house. It was warm and the smell of fish was in the air. It made her hungry.

This sentence correctly used past tense consistently throughout the entire paragraph.

4. Possessives vs. Contractions

Aside from these heavy grammatical errors, another common mistake is leaving out the apostrophe—or adding one when it isn’t necessary. The most common ones are as follows:


Remember that “your” means it belongs to you; “you’re” is the contraction for “you are.”


When something belongs to “it,” it’s “its.” When it is a contraction, use “it’s,” or “it is.” Don’t forget: the apostrophe for “it” is actually the contraction, and lack of an apostrophe belongs to the possessive.


This is a grammatical error we’ve all been working on since first grade. “Their” is when it belongs to them; “they’re” means “they are.” They sound the same, but the meaning is so different!

5. Affect vs. Effect

Although once you understand the difference here you’ll be kicking yourself over how easy it is, many people struggle with the difference between “affect” and “effect.” Allow me to bring the final say on this so that you never question it again.

“Affect” is usually the verb form of this word, meaning to “influence.” If endangered tigers are going to be bothered by deforestation, that means they’re affected by it. When we release CO2 emissions from our cars, we’re affecting the environment.

“Effect” is usually the noun form of this word meaning “a result.” It’s the person, place, or thing. The effect of deforestation is endangered tigers. The effect of emissions is pollution.

Affect is an action; effect is a thing. Hope that clears it up!

Note: In some cases, the parts of speech are reversed, but this doesn’t happen all that often. “Affect” can also be a noun meaning “display of emotion”: The woman’s affect changed when she saw her lost cat. “Effect” can also be a verb meaning “to bring about”: You will effect change if you rally the troops.

6. Misplaced Modifiers

One mistake that’s easy to make is placing a modifier so far away from the subject that the sentence contains a completely incorrect meaning. A modifier is a word or phrase that describes a noun. For example, if you’re writing about a woman planning for a party, be careful not to do this:

Cleaning the kitchen for the party, the dishes were neatly stacked by Mrs. Ashby.

It sounds like the dishes were cleaning the kitchen! To prevent sentences where inanimate objects are given tasks, make sure the subject—the person or thing exerting the action—is right next to the description. In this case, the correction would be something like this:

Cleaning the kitchen for the party, Mrs. Ashby stacked the dishes neatly.

Now Mrs. Ashby is right next to the phrase about cleaning, making it clear that she was one cleaning the kitchen, not the dishes. It’s not Beauty and the Beast, after all. 

7. Who vs. Whom

In this all-too-frequent grammatical error, writers forget which is the subject and which is the direct object. “Whom” is rarer than “who,” simply because “whom” is only used when it’s the object of a preposition or verb. Since most of the time people/living beings are the subject of the sentence, and not the object, “whom” is appropriate less often than most people realize. You only need “whom” in a sentence like this:

She went to the dry cleaner’s, and they asked for whom they should prepare the pick-up ticket.

As you can see, “whom” is often included in phrases like “for whom,” which display its use as the object of a preposition/verb. Most of the time, you’re going to use “who.” Bet you didn’t know that!

What are your common grammatical errors?

We’ve touched on some of the most common and annoying grammatical errors that writers make. Are any of these your mistakes too? Do you see how to correct any bad habits? Use this article as a guide the next time you revise your own writing; you might find that you make more (or fewer!) mistakes than you realized.

Like what you saw?



Sally Baggett

About The Author