5 mistakes non-native speakers make when they write in English

English is the international language of science (and global communication). To be valued as a scientist, you must express yourself in good English. But there are some pitfalls that non-native speakers tend to fall into. In this post, you will discover some of these traps and you will be prepared to get around them at the next opportunity.

Why words matter

A long, long time ago, when I was a master’s student in psychology, I was looking for a mentor to supervise my Ph.D. thesis. I had managed to get an appointment with Eric R., a researcher at the University of Toulouse, where I was studying. I was thrilled to meet him because Eric was (and for sure still is) a brilliant mind with a certain coolness that made me even more eager to impress him.

So Eric and I meet for lunch to discuss the possibility of working together, and I start explaining the ideas I have for my Ph.D. thesis. I wanted to work on the emotion of remorse and to show how this emotion differs from regret and guilt. I had a whole theory in mind that I wanted to share with Eric. “My goal is to circumcise the emotion of remorse. Circumcising emotions is fundamental. This circumcision will help psychologists better understand these emotions, yadi, yada…” After a while, I stop talking, and Eric looks at me and says with a grin on his face, “you mean circumscribe, don’t you?”.

Circumcision is the removal of the foreskin from the human penis. Circumscription is the act of restricting something with limits. In my excitement, I had mixed them up. Eric was a nice guy with a great sense of humor. He corrected me gently and probably rejoiced in an anecdote that he could tell his friends at the next dinner party. As for me, this incident reminded me that words matter.

Words written with Scrabble blocks

It’s hard enough to find the right words in your own language, not to mention the challenge of a foreign language. In this article, I have listed some of the most common mistakes that we, non-native speakers, tend to make when speaking in English so that you don’t end up uttering insanities when you’re trying to appear intelligent and competent.

1. Affect vs. Effect

The distinction between affect and effect is quite complex because the two words have several meanings.


  • Affect used as a noun describes an emotional state. For example, you may say “I told him that it was over between us, but he didn’t show any affect“. Similarly, in the context of a psychological article you could write “We measured participants’ affect before and after the experimental manipulation”.
  • Affect used as a verb means “to influence” or “to produce a change”. For example: “The drug affected the patients’ recovery” or ” Gravity affects the movement of objects” or “Cancer symptoms vary depending on which part of the body is affected“.
  • Affected is also an adjective that describes a person who is unnatural, artificial, or even pretentious. For example: “She took an affected pose and pretended not to care”.


  • Effect is usually used as a noun and means “the result of an action” or “the result of a change”. For example, “The intervention did not produce the expected effects” or “The earthquake had devastating effects”. This meaning of effect is not that different from affect, which is probably why we tend to mix them up. One could say that effect (the noun) is the result of affect (the verb).
  • Effect can also be used as a verb. It means to “put into operation” or “bring about a change”. If you say “I effected changes in my manuscript,” it means that you implemented these changes, i.e., that you already made them.

I know, it’s tricky! If it’s not quite clear yet, check out this Grammarly post, which is entirely devoted to the distinction between “affect” and “effect”.

2. Relation vs. Relationship

The difference in meaning between these two words can lead to weird misunderstandings because one term refers more to the private sphere and the other one is common in the scientific field.

Relationship is used to describe a bond between two people. You would talk about the relationship between a mother and her child, or a romantic relationship.

Relation is used to describe an association between two variables. For example, in an article, you may write “We did not find any relation between participants’ diet and their blood glucose concentration.”

3. Irritated vs. Confused

This mistake is particularly frequent for native German speakers.

I remember the first time my German colleague told me that she was irritated because of something I had done. My heart skipped a beat, my mind started racing, wondering what I had done to upset her, and I expected us to come into conflict. At the same time, she seemed relaxed and open so I thought “wow! Germans are so direct and have amazing control over their emotions”. The Germans are those things, but that’s not what was happening over there.

In German, irritiert means confused, puzzled, or perplexed. It’s a false friend. In English, to be irritated means to be slightly angry, annoyed. It is a rather unpleasant feeling. So be careful when you use this word because it can lead to awkward situations.

3. Efficient vs. Effective

I must always double-check this distinction. Somehow I don’t seem to remember it. Probably because both words refer to the ability to produce a result.

Efficient means “capable of producing results without wasting resources”. If you are reading this blog, you probably want to increase your efficiency. Being more efficient means being faster or better.

Effective means “producing a desired result”. The only thing an action needs to be effective is to produce a result. It doesn’t matter how big that result is.

One way to better appreciate the subtle difference between these two terms is to illustrate it with a medical example. Imagine that you have tested two treatments. It’s possible that both were effective, but one may have been more efficient than the other. This result would indicate that both treatments improved symptoms, but that one was more successful than the other.

4. Lend vs. Borrow

Another common mistakes that non-native speakers make in English lies in the use of lend and borrow.

Lend means ‘to give something to someone for a short time, expecting that you will get it back’. For example, “I lent my sister €100 because she lost her wallet”.

Borrow means to ‘get something from someone, intending to give it back after a short time’. For example: “Could I borrow your car tomorrow, I need to get out of town?”

5. They’re vs. Their

If you tend to mix these two words together, you need to straighten this out as soon as possible. From time to time, I see this mistake in an article or a thesis that I have to review and let me tell you that it makes a terrible impression. So, here it is, once and for all :-).

They’re is the contraction of they are. It can refer living things, such as two persons: “they’re best friends” or inanimate things: “they’re both good articles”. In general, you shouldn’t use this kind of contraction in an academic paper. It’s far too colloquial.

Their is the possessive form of they. It refers to what belongs to or is associated with people or things previously mentioned or easily identified. For example, “They went back to their university” or “they lost their temper”.

That’s all, folks! I hope these few tips were useful. If you’d like more tips to improve your writing in English, check this post on my favorite software packages and applications for writing. You’ll find there great tools to avoid and correct the mistakes that we, non-native speakers, tend to make in English.

Affectionately yours,


Dictionary cover photo by Pisit Heng on Unsplash

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  1. Birgit 18. December 2020 at 9:27

    Thank you for that list. I enjoy reading your articles.
    Here are a few more words that my students often mix up:
    * its – it’s
    * a proof – to prove
    * is safe – to save
    * were – where
    * to – too
    * adapt – adopt

    1. Gayannée Kedia 18. December 2020 at 9:53

      Thanks a lot, Birgit, for this input! That’s true, I’ve also found these mixups in my students’ papers. Where do you teach, if I may ask :-)?

      1. Birgit 10. January 2021 at 17:17

        TU Graz. In November, I took part in your online writing seminar at TU Graz and I enjoyed it at lot.