“Where’s Trutnov?” I asked.
One of my Czech friends was trying to tell me but she was having problems. She confessed – a little embarrassed – that she always confuses the English words for “east” and “west.”
And she didn’t know why.
A couple weeks later, while I was building my own vocabulary by reviewing my Czech flashcards, I noticed I was mixing up the words for “push” and “pull.”
And I didn’t know why.
But then…I found out!
The answer… interference theory!
And yes, it’s as boring as it sounds. If you have trouble sleeping at night, you can read some academic papers written about it.
But let me save you the pain and suffering.
INTERFERENCE THEORY: when you learn two or more words at the same time, and the words are related (ex. types of metals, names of trees, a list of phrasal verbs for movement, etc.), your brain doesn’t like it and will make you feel stupid when you try to remember them.
Advertisers have known this for a long time. They know that if you see a commercial for a Skoda and then immediately after it a commercial for a Fiat, you’re less likely to remember which had the new brake system and which had the new heated seats. So instead, Fiat chooses to play their commercial after the latest “Fast and Furious” movie trailer.
But what did we do in school? Exactly the wrong method! We learned a list with all the fruits…a list with all the colors…a list with all the farm animals, and so on.
It seemed like a logical and organized way to build your vocabulary…but you can’t argue with research.
In one of the first studies done on this subject, it took students 7.2 repetitions to learn a list of non-related words while it took the second group 11.3 repetitions to remember a list of related words.
That’s a 35% difference!
And in another study, the researchers saw that it took longer to recall a word that was learned in a related group.
Ex. I would like to buy a ….(pear? mellon? peach?)…apple!
So next time you learn a new word and want to write it down in your notebook, resist the temptation to write down similar words.
I still have this temptation when I make flashcards. When I made the flashcard for the Czech word for “narrow” I thought, Well, it would be useful to also learn “wide.”
But then I remembered the wise words from the boring research study, “Overall, then, presenting semantically grouped L2 words to learners has a deleterious effect on learning.”
And I resisted learning the word for wide…for now.
 https://personal.maccs.mq.edu.au/~mfinkbei/papers/finkbeiner & nicol, 2003.pdf
 A real vocab list from one of my business English text books – now gathering dust on the shelf.