10 Common Grammar Mistakes (and How to Fix Them)
You can have a brilliant argument, solid research, and a clear structure, and still lose marks to a stray apostrophe. Grammar mistakes are frustrating precisely because they feel small — yet to a reader, they quietly suggest the work was rushed. The good news is that most of the errors students make come from a short, predictable list. Learn that list once and you will keep catching the same slips for the rest of your academic life.
This guide walks through the mistakes that show up most often in essays, lab reports, and applications, grouped so they are easy to remember. For each one you will see the wrong version, the corrected version, and the rule underneath — because the aim is not to memorise a fix but to understand why it works. Once the reasoning clicks, you stop second-guessing yourself and start writing with confidence.
Confusable words that sound the same
English is full of words that sound identical but mean different things. A spellchecker rarely flags these, because each spelling is a real word — it is just the wrong one for the sentence. That means you have to catch them yourself, and the trick is almost always a quick mental test.
Wrong: The dog wagged it’s tail. Right: The dog wagged its tail. It’s is always short for it is or it has, so read it that way to test it. If the dog wagged it is tail sounds absurd, you want the possessive its with no apostrophe.
Wrong: Your going to love this seminar. Right: You’re going to love this seminar. You’re means you are, while your shows possession, as in your notes. Expand the contraction in your head — if you are fits the sentence, use you’re.
Wrong: Their going to leave they’re bags over their. Right: They’re going to leave their bags over there. They’re is they are, their is possessive, and there points to a place. Say the sentence slowly and match each word to its job.
Wrong: The medication had a strong affect. Right: The medication had a strong effect. Affect is usually the verb (to affect something), and effect is usually the noun (the result). If you can put the or an in front of the word, you want effect.
Wrong: She is taller then her brother. Right: She is taller than her brother. Than compares two things, while then is about time or sequence, as in we revised, then we slept. If you are comparing, it is always than.
Catch grammar, spelling, and clarity slips while keeping your own voice — free.
Grammar Checker →Apostrophes and punctuation
Punctuation carries meaning as much as words do. A misplaced comma or apostrophe can change how a sentence reads, or make a grader stumble exactly where you wanted them to glide.
Wrong: The experiment failed, we ran it again. Right: The experiment failed, so we ran it again. Two complete sentences cannot be joined by a comma alone. Fix a splice with a full stop, a semicolon, or a joining word such as and, but, or so.
Wrong: The student’s arrived early and handed in their essay’s. Right: The students arrived early and handed in their essays. Apostrophes show possession, not plain plurals. Add one only when something belongs to someone, as in the student’s essay.
Sentence structure that reads clearly
These mistakes are about how a sentence holds together. They are the easiest ones to miss when you reread in your head, because your brain quietly fills in what you meant to write rather than what is actually on the page.
Wrong: I studied all night I still felt unprepared. Right: I studied all night, but I still felt unprepared. A run-on jams two complete thoughts together with nothing between them. Give each thought room with a connector or a full stop.
Wrong: Because the deadline moved. Right: We finished early because the deadline moved. A fragment is missing a subject, a verb, or a complete thought. Read it on its own — if it leaves you waiting for the rest, it is not yet a sentence.
Wrong: The list of sources are on the next page. Right: The list of sources is on the next page. The verb has to match the true subject. Here the subject is list, which is singular, not sources, so it takes is.
Wrong: Walking to class, the rain soaked my notes. Right: Walking to class, I watched the rain soak my notes. An opening phrase should describe the subject that follows it. As first written, the sentence claims the rain was walking to class.
Wrong: The author argues her point, then she described the results. Right: The author argues her point, then describes the results. Choose a tense and stay in it. Sliding between present and past blurs the timeline for your reader.
None of these rules need a grammar degree — just a little attention and the habit of rereading before you submit. Read your work aloud, watch for the patterns above, and most errors will surface on their own. When you want a second pair of eyes, a quick check can flag the slips you have simply stopped seeing.
Catch grammar, spelling, and clarity slips while keeping your own voice — free.
Grammar Checker →