One letter, opposite meaning
"I am boring." You meant that you were bored. What you actually said is that you are a boring person. The sentence has no grammar error in it, nothing looks strange, and that is the whole problem. Nothing warns you. This pair of endings is worth two minutes of your life, because the rule behind all of them is one line long.
The whole rule
6 pairs IELTS students use most
bored / boring
✕Students are boring in long lectures.
✓Students are bored in long lectures, because the lectures are boring.
The wrong version says the students themselves are dull company. Notice how the corrected sentence uses both forms once, which is a neat way to prove you control the pair.
interested / interesting
✕I am very interesting in this subject.
✓I am very interested in this subject, because the subject is interesting.
Interested takes in after it, every time. Interested in, and never interested on or interested about.
confused / confusing
✕Many students feel confusing when they read the question.
✓Many students feel confused, because the question is confusing.
A person cannot feel confusing. Feel, become and get are followed by the person form, so they always take -ed.
worried / worrying
✕Parents are worrying about screen time.
✓Parents are worried about a worrying trend.
Worrying means it makes other people worry. This one changes who is doing what, so it can genuinely confuse a reader rather than just sound off.
satisfied / satisfying
✕Workers are more satisfying when they choose their hours.
✓Workers are more satisfied when the job is satisfying.
The same shape appears with frustrated and frustrating, excited and exciting, relaxed and relaxing. Learn one pair properly and you own the whole family.
tired / tiring
✕The journey was tired.
✓The journey was tiring, so everyone arrived tired.
A journey cannot feel anything, so it cannot be tired. Objects, tasks and days take -ing. People take -ed.
Three small rules that come with it
✓After feel, get, become and seem, use the -ed form. They all describe a person.
✓Interested takes in. Worried takes about. Satisfied takes with. Learn each with its partner.
✓If the word describes a job, a lesson, a film, a day or a result, it is almost always -ing.
Why this counts twice
It is tempting to call this a typo. It is not scored as one. Because the sentence stays grammatically correct, the examiner does not read a mistake, they read a meaning you did not intend, and then the next sentence does not follow from it. That shows up as a grammar slip and as imprecise word choice at the same time. Very few errors this small cost you in two criteria at once.
Read next
More pairs that never feel wrong: affect or effect, and 9 more and a, an, the: the three smallest words that cost the most marks.
Catch the ones you cannot see
This is the kind of error you will never find by re-reading, because you know what you meant and your eye supplies it. Write your next essay in VoyaLang and read the corrections. Each one is marked inside the sentence you actually wrote, with the right form beside it, so you learn the pattern from your own words instead of from a rule. Create a free account and check your next essay in about a minute.
