I am on a physics course. Often I struggle with following mathematical derivations, so I aim to scrutinize them very carefully to make sure I understand them. Sometimes I find mistakes in the lecture notes, which are harmless from the overall point of view (ie we get the same result, it won't affect subsequent lines). Nevertheless, they are wrong. Ie instead of writing J(x) (J as a function of x), lecture notes contain Jx, ie function of J times x. We mean the former, and later use the former interpretation. Or: writing exp(0-), where 0- is the limit of x as x approaches 0 from below, while the right thing which follows from the previous lines would be exp(-0-). Of course these are equal so not much harm done, but it is still wrong. Or when on the lecture it is said that "do check this at home you will get X", and I go home and check it and the answer is not X, that seems to be problematic. Almost noone bothers to check though, so it doesn't seem to be a big issue.

My usual reaction to this is to write a kind email to the professor to point these out. I thought it is useful for both of us, he gets to correct a typo, or I get to learn something new in case it is not a typo & I am wrong. I noticed though that this is not something common to do. Once I checked this on a course, and more than half of the entries on the list of erratum in lecture notes are the things I have pointed out. Am I a weirdo and I should stop pointing these out, or this is normal behaviour?

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    What is the professor's reaction to your comments? The fact that they maintain an erratum suggests that they see it positively. Some professors create a collection of notes that they refine and keep using for future offerings of the course, so you are probably helping future students as well.
    – GoodDeeds
    Nov 21, 2020 at 14:15
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    It really depends on the prof. And sometimes, physicists have good reasons to not be as wxact as mathematicians
    – user111388
    Nov 21, 2020 at 14:27
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    I am usually sent a "thank you for pointing that out" or something like that message, or I get no reply. In the former case I continue my habit, in the latter case I usually stop. Nov 21, 2020 at 14:27
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    Professors sometimes plan to eventually turn their lecture notes into a book. That would make them particularly grateful for corrections. Nov 21, 2020 at 16:00
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    Is J a linear map? Then Jx is actually standard notation (but the mistake in the notes is not to mention this). Also why would 0- not be the limit from below? Generally I would say: yes, people are happy about having pointed out even the smallest typo, but you shd check with some other student if these really are typos.
    – lalala
    Nov 22, 2020 at 9:17

2 Answers 2


I think it is a good idea. While the typos you find may be harmless in their respective contexts, they can be a hindrance to properly understanding the concepts, particularly for students who find the material challenging and are not immediately able to identify when something is just a typo. A harmless typo, such as an incorrect expression that just happens to match with the correct answer for a particular problem, can lead to errors if applied to other problems. Furthermore, "do check this at home you will get X" not giving X is not harmless — students would not be sure if they did not get X because they applied a method incorrectly or because it was just a typo, which would waste time and cause confusion, as you also mentioned.

Whether you should report the typos depends on the professor. If they explicitly encourage students to report them, then certainly you should. If there is no explicit guidance, then unless they react negatively to your corrections, it would be a good idea to inform them, and as you say, get a confirmation that your understanding is correct. If you are still in doubt, you can always ask what they would prefer.

In your specific case, the fact that they maintain an erratum suggests that they see it positively. Some professors create a collection of notes that they refine and keep using for future offerings of the course, so you are probably helping future students as well. In fact, some may encourage it to the extent of giving extra credit for finding errors.

I am not aware if it is "conventional" or "normal" behaviour in general, but I see no reason to not do this, as long as your corrections are accurate, useful, and you have the (even implicit) support of your professor.

  • If others in a class might be misled in some way then it might actually be essential to point out errors.
    – Buffy
    Nov 21, 2020 at 15:30
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    @Buffy Agreed, but it will be successful only if the professor is receptive. Some may see it as "yes, it is not exactly correct, but you get the point being made" and leave it at that, even if it could be misleading to other students.
    – GoodDeeds
    Nov 21, 2020 at 17:44
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    I know it's a bit against the policy to say thanks in the comments, but thanks a lot. Most of the time I spent studying any course was figuring out whether something is a typo, or it has a deeper meaning that I am just missing. It is difficult for me, and I assume many, to dismiss an authoritative source as a typo when the entire reason I am even reading the thing is the implication that I know less than the source.
    – Andrei
    Nov 22, 2020 at 16:33
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    When I was an undergraduate, most lecturers downright encouraged us to aggressively hunt for typos. One first-year circuit theory lecturer brought a chocolate bar to each lecture, as a reward for the first person to find the (deliberate) typo in that lectures' notes. Of course, some had >1 typo in them, and thus you weren't allowed to eat the chocolate bar until after the hour was up, lest you have to subdivide it into (n_typo_finders) pieces beforehand...
    – Landak
    Nov 22, 2020 at 16:45

Culturally, some physics people seem to take pride in using notation that's just sloppy - expecting the reader to figure out what was meant from the context if they understand the physics. For example, Lev Landau (Nobel 1962) sometimes wrote just T (temperature) when he meant kT (energy = constant * termperature). He also sometimes wrote "(something)/2mT" when he meant "(something)/(2mT)". He figured, if you understand the context, you can't possibly misinterpet this as "(something)/2 * m *T". My own grandfather was a physics professor and sometimes wrote like this too (they both studied under Abram Ioffe). I heard a plausible conjecture that some physicists who write like this, studied Hebrew as children and were taught to write just the consonants without the vowel signs, and expect the reader to figure the vowels from the context.

In my opinion, learning to decipher what the writer meant, from the context, as opposed to what they literally wrote, is still a useful skill for a physics major to learn. (Less so in other disciplines, such as economics or chemistiry, where most people aim to make their mathematical notation as readable as they possibly can.)

But there are way more than enough examples of this phenomenon in physics papers to master this skill. Helping make your class notes better for future generations is a noble goal. You also learn something in the process. Your instructors don't seem to mind (they maintain the errata). As long as they don't tell you that your corrections are over the top, you should keep going.

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