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Is it normal to forget most previously learned material?

  1. May 20, 2012 #1
    Every semester, whenever I begin to learn a new subject, that is, a more advanced class of the previous subject (i.e. algebra -> pre-calc -> calc -> diff eq, etc.) I forget a lot of the stuff I learned in the previous class when I'm learning the new content and constantly have to review all the time because I keep forgetting the basics and it's interfering with the more advanced classes...is this normal or should I hammer the bases more into my head so I will never forget them and not have to look back every time I need a formula or theorem and whatnot?
  2. jcsd
  3. May 20, 2012 #2
    If you have the time and a real interest in the material, yes. Forgetting material is also an indication that it was not learnt well in the first place. Usually when I learn something well, it becomes second nature.
  4. May 20, 2012 #3
    This happens a lot more with physics than with math but that is largely because the math *I'm* doing (for the time being) is usually more geared towards problem solving, whereas those in physics (even simple, algebra-based physics) involve the description of physical systems and understanding (and also remembering) various laws and such.

    What happens is that I may forget how something in a physics topic works, say, the motion of a particle down a slope. However, if I were to take a few minutes to review everything, I would be able to solve the problems. Perhaps, as the previous poster has noted, you have not *thoroughly* learned the material before. Studying doesn't have to be hard. Try a few problems on every different chapter every day or so (also: they're interlinked, you'll see high school algebra everywhere, pre-calculus in calculus, calc in DEs and so forth) and see if you notice any changes.

    You have to stay in touch to remember. I guess that with some subjects, it's more like walking or cycling (you don't easily forget those) than the others.
  5. May 20, 2012 #4


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    It does seem common to forget most of each course. At least that was the case for most of my students for 30+ years in university classes. I eventually learned to teach essentially every class from scratch, as if the students remembered virtually nothing from previous courses. Even when teaching graduate PhD candidates, I always had to review the two most basic theorems of advanced calculus, the implicit function theorem and Green's theorem.

    This always puzzled me because I had not forgotten myself essentially anything I had learned in high school math classes for my whole life. I had participated in math contests regularly, stayed after school to practice for them, and probably benefited from that extra practice at learning reinforcing and using the material.

    But I am convinced my students' forgetting showed that many of them never really learned the material well at all. Basic study habits such as reviewing the material every day after class, would have made impossible the sort of situations I faced every day. Other students made it clear to me that they never studied at all on weekends, regarding them as purely for social activities.

    Office hours were routinely ignored, no questions asked in class, and questions were never raised until the day before, sometimes hours or literally minutes before a test.

    Some students seemed to think that the prerequisite for a class was simply to have taken the previous class even getting a D in it, rather than to have learned and retained the prerequisite material. You would think it obvious that if algebra is a prerequisite for calculus, and a student has forgotten all his algebra, that he would realize he does not have the prerequisite, and that he would review algebra in the summer perhaps before taking calculus. However this seemed uncommon behavior.

    Perhaps some of my students, certainly not all, thought that the only purpose in taking courses was to get a degree, rather than to learn what was taught in the courses. Perhaps some thought that a degree, rather than knowledge, was the key to a good job. Some students focus entirely on passing the class rather than learning the subject. For this reason some seek out the easiest teacher,f rom whom they will learn least, rather than the most demanding teacher, who will push them the furthest.

    This may be partly the fault of those of us who teach without giving any indication of how the material we teach will be used. If we tell students why they need to know something, maybe it will help. [this has been edited.]

    By the way, the fact that you are asking this question shows that you are motivated to improve your study skills. More power to you.
    Last edited: May 20, 2012
  6. May 20, 2012 #5
    OP, by any chance, have you attempted such a method? Throughout most of high school, I coasted through my courses simply by turning up and paying attention to my classes. It was a bad idea but I had then, very little interest in what I was doing and simply found my classes as either "dull" or "kinda cool" and not "out of this world insane!
    I'll keep doing this until I fall asleep out of fatigue!". When I started learning more complex material, be it mathematics or literature, I found that just "turning up" was never enough. Around that time, I had begun to develop a deeper interest in my work and now, it's come to a point that I regularly review what I've learned.

    It is also helpful to note that this method is not "boring" or "insanely hard". At least, it isn't for me and it seems to work! Really, it's just a matter of sitting down for at least one solid hour (YMMV, depending on how well you grasped the subject...) to read and make sense of/understand the theory and then working out a few exercises. You don't have to do one hour's work in one go. Breaking it down into 20-minute chunks is fine, as long as you pick up where you left off shortly after. What is key is finding something that works for you!

    This brings us to another interesting question: "how does one form an interest?". If one* can figure out how that works, then stimulating an interest in a subject (even if just for the duration of a course) becomes possible.

    *Whether one is someone teaching a course to an uninterested group of individuals or one who has to learn something they are not interested in.
  7. May 20, 2012 #6


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    I also thought just showing up, if I did even that, was enough. I flunked out of college after a while with this approach and when I got back, without any review of prerequisite material, started off with a D on the first test in the next class. Faced with getting kicked out again, and this time for good, I began reviewing the lecture every day for one hour after class in the library. Then I also bought a practice book, a Schaum's outline, and did extra work. Finally I began looking up in other books, material to fill gaps in the class presentation. On the final, I got 100, not the only one, but the prof said it was "head and shoulders above the rest of the class".
  8. May 20, 2012 #7
    There are two issues.

    1. How was the material taught?

    Proof classes always allow me to remmember things much easier, if it's a formula based class I generally forget right away. Learning how it was mentally derived makes things easier to remmember.

    2. How much information were you having to take in that term?

    If you're taking 4+ difficult classes, most people won't remmember much of anything, they are too busy trying to cram everything and don't have time to really think about whats being covered.
  9. May 20, 2012 #8
    In high school, paying attention in class was just enough for me to maintain grades in the 90s, which I was content with. It didn't start cutting it later on though, and the same thing that happened to you guys also happened to me.

    Anyway, how I usually study now is I kind of break up the study material by the description of the syllabus and when exams take place. I will study right after class and throughout the week, continuously reviewing all relevant material until the point of the test, then never study that stuff again because I begin to focus on the next exam. And then for the end of semester exams, I will just compress the entire study load into a shorter period of time but by then it won't have been long enough for me to entirely forget what I learned for the entire semester.

    The forgetting happens typically after an extended hiatus such as summer break and when I start taking new classes...by the time it comes for the semester after that, I will have probably forgotten everything I learned two semesters ago.
  10. May 20, 2012 #9
    I forgot most of the math I learned, and I used to be really good at it. If you don't use it, you lose it unless you are gifted with a photographic memory. I mean I understand the important concepts still, like what is a derivative, what is an integral, etc. but if I had to do an integration by parts right now, I probably couldn't do it since I haven't done it in about 10 years. The important thing is just to be able to recognize what the problem is at hand and where to go to look up how to solve it. If I did a few problems to refresh my memory, I could probably get back into the groove of things.
  11. May 20, 2012 #10
    I think I remember reading that you only retain something like 1% of what you learn
  12. May 20, 2012 #11
    Well it depends on what your forgetting. If you forget something like the derivative of x, then you have to question your knowledge of the material because it is supposed to be very intuitive.
  13. May 20, 2012 #12
    That's a bit misleading when you consider all of the different information that you experience throughout a day; maybe you read the nutritional info on the back of a cereal box when eating breakfast because you were bored - of course you're not going to remember insignificant things like that... but studying for a test - that's most likely going to stay in your long-term memory
  14. May 20, 2012 #13
    Not for me, I got a 100 on a math test, and within a week I had no idea how to do anything.
  15. May 20, 2012 #14
    lol you're right
  16. May 21, 2012 #15


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    I understand your students opting to save weekends for socializing, wish I had done it...
  17. May 21, 2012 #16
    Then you had an incredibly flimsy understanding to start with and/or the exams were incredibly easy.
  18. May 21, 2012 #17
    Oh no, I just have old people's tests and I memorize whatever they did on their test and do it on my own (the questions are similar enough semester to semester that I can figure it out most of the time and always get 95%+ on the tests). yes I know it's incredibly flimsy, but I'm going into the final with a 99% so all I need is a 56% on the final to keep my A
  19. May 21, 2012 #18


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    you are wasting your (and professors') time and your (parents') money. you seem to have perfected a system for sailing though school with no residual knowledge at all.

    I am afraid you are going to be a very sad young person when you find out afterwards that not knowing anything at all means you are unqualified for any employment whatsoever. yes even with a "degree".
  20. May 21, 2012 #19


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    Why are you even at university?
  21. May 21, 2012 #20
    I blame the education system being so rote. Maybe if they tested concepts instead of memorizing cookbook steps to answering anything my ploys wouldn't work. I am the first to admit I have no idea what Green's theorem is, but I did it on my final today and computed it correctly, all I did was follow the steps as done on previous quizzes. Easiest A in my life

    oh yeah, and stop putting so much pressure on me to get all A's and maybe I wouldn't cheat the system. Professional school's emphasize A's a lot more than understanding the concept, so I'm just doing what I gotta do to get a secure high paying job.

    Don't blame me.

    And i'll be doing the same exact thing next semester in differential equations
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