Why we Forget?

ForgettingForgetting is defined as the inability of retrieving the information we learned. It is an annoying attribute of our memories. Just remember how many times you couldn’t recall important information, like a crucial mathematical formula in a math exam. I have experienced this, and it was extremely annoying.


What’s happening to our minds and we can’t remember? Scientists were also interested in finding the answer to this question. There is a lot of research on this topic. Let’s find out.


The Research


The rate of forgetting is a topic that first the German philosopher Hermann Ebbinghaus initiated a scientific research on it. His intention was to measure it.


His experiment was first to create lists of many meaningless three-letter syllables. Then, he measured the amount of time he needed to learn these lists flawlessly to the point on writing them down without making any mistakes. Next, he tested his memory by trying to rewrite the lists after a period, ranging from 20 minutes up to 31 days.


Ebbinghaus research resulted in a significant discovery. That was that we forget more rapidly in the beginning rather than after a long time. The next example makes this clearer.

The Seven Sins of Memory: How the Mind Forgets and Remembers
How the Mind Forgets and Remembers



Let’s say that you are reading an article in a magazine. When you finish it, you realize that you cannot remember some details of the stuff you had just read. While minutes pass, you realize that more information cannot be retrieved. In the end (after days), you will remember only the main concept and some meaningful to you details.


You’ll be able to recall some bits of information after some time, but if you never again hear or see something relevant, it’s possible to forget that info forever.



Ebbinghaus results were summarized and represented graphically in a two axis system. In the vertical axis were the percentages of correct answers and in the horizontal axis was the passed time. The graphic representation was a curve with a high bent in the beginning, and a declining bent as the time was increasing.


The curve showed the relation between the recall capability and the time that passed, from the items presentation until the memory test. Other scientists also agreed on the Ebbinghaus curve.




While Ebbinghaus experiments measured the rate of forgetting in the long-term memory, many researchers tried to measure the same in the working memory. They did an experiment that was similar of Ebbinghaus’s.


They asked the subjects that participated in the new experiment to try remembering three-letter syllables after a delay of 3, 6, 9, 12,15 and 18 seconds. In the meantime, they also prevented the subjects to mentally rehearsing the syllables by asking them counting reversely from a random number.


Although memory loss in working memory occurs rapidly at the first moments, the experiment’s results were similar to the Ebbinghaus’s  experiment. They followed the same general pattern; that’s high forgetting rate initially and a declining rate as time passes.


Decay Theory of Forgetting


This is one of the oldest theories about memory loss. The problem with this approach is that it is more a description rather than an explanation.


This theory suggests that when we learn something new, this initially is a single entity that gets fragmented over time. As you understand, this is just a description.


Another problem that scientists faced with this theory is the fact that people may be unable to remember a bit of information at a time while they can remember it perfectly later. This is called reminiscence, and it would be impossible if memories get decayed over time.


Because of these two issues, the Decay Theory became obsolete, and researchers support now a new theory: The Interference Theory.


The Theory of Interference


The interference theory argues that forgetting occurs when other activities, information or experiences interfere with our memory.


At 1924, an experiment took place by two American psychologists, John Jenkins and Karl Dallenbach. The subjects were two students that they had to learn lists of nonsense syllables. The experimenters tested the subjects’ memory after 1, 2, 4 and 8 hours.


The results were grouped into two categories. These categories were differentiating by the number of activities the two students experienced between learning and testing.


For the results of the first group, the students learned the lists just before the bedtime. They took the test just when they woke up.


For the results of the second category, the students learned the lists just when they woke up. They got tested after the above referred interval times.


In the first category, the students didn’t have any activities in the meantime between learning and testing. In the second category, the students were awake in the meantime between learning and testing. So unavoidably they performed some activities in the meantime before taking the test.


When the two psychologists compared the results of the two groups, they found that both students had greater success when they had learned the lists just before sleeping.


This led the scientists in the conclusion that the reason of forgetting is the amount of activities that interfere with our memories.


There are two types of interference: The Proactive and the Retroactive interference.


The Proactive interference refers to the old memories that interfere with new information, and Retroactive interference refers to the new information that interferes with old memories.


Another related issue is the Repression. Sigmund Freud proposed this term, and it points to the tendency of failing to remember unpleasant memories. Repression may also be the cause of forgetting old traumatic memories like a hard childhood or unpleasant future activities, such as a boring appointment.


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