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$\begingroup$

I'm not a native English speaker. A quick Google search revealed the symbol's name is apostrophe, just like in French. When used in a mathematical setting, I usually call it prime, so for instance $f'$ I'll read $f$ prime. That's the way you call it in French, but I just realized I didn't actually know whether that was the way you call it.

Thank you!

  • 1
    I am guessing it is region dependent. I am more familiar with "dash" when talking about derivative. So $f'(x)$ is f-dash x. The pronunciation could also vary with context, I suppose: when it means something other than derivative etc...2011-06-24
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    This is part of a larger issue: Some symbols are pronounced using their name, and some are pronounced, at least in certain circumstances, using a special name. Besides the appostrophe being pronounced "prime" (when used to indicate a derivative), there are also the cases of the ampersand (&) being read "and" and the asterisk (*) being read "star".2011-06-25
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    Strictly speaking, the [prime](http://en.wikipedia.org/wiki/Prime_%28symbol%29) (′) is a different character from the [apostrophe](http://en.wikipedia.org/wiki/Apostrophe) (').2011-09-02
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    I would also read it as f prime.2011-09-02
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    It is not a good notation, $\frac{df}{dx}$ is far superior to this form.2011-09-02
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    @Arjang: Not at all! If I have $f$, I can write $f(x)$, $f(y)$, $f(5)$, $f(a+b)$, and so on. Why should just $x$ go in the denominator as though it were a free variable? To be precise, $f$ is a function mapping reals to reals and has nothing to do with some $x$, unless you write $\frac{df(x)}{dx}$ as you properly should. But the prime is better, because it doesn't require you to introduce a name for the argument of $f$. Then I can write $f'(5)$ for the derivative of $f$ evaluated at $5$, instead of $\left.\frac{df(x)}{dx}\right|_{x=5}$ (yuck)!2011-09-02
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    @Rahul : $f'(5)$ wins a point, however I am a devout follower of Leibniz :), but still a good point is a good point. also I like your obsorvation about not introducing extra variables, It seems intresting topic for a question2011-09-02
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    @Rahul: Heh, that reminds me: I bought [this](http://books.google.com/books?id=UrSnNeJW10YC) the other day and the authors insisted on keeping the prime just for denoting a "different" function, and insist on Leibniz notation everywhere else. I mean, it was sort of jarring to see what [Taylor looks like in that notation](http://books.google.com/books?id=UrSnNeJW10YC&pg=PA4) (equation 0:5:1).2011-09-06
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    @Arjang: the book I was point out to Rahul might interest you. :)2011-09-06
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    As everyone is pointing names for this, in portuguese it reads "f linha" (literally, "f line") - and it is not an apostrophe nor a simple quote opening.2013-06-14

3 Answers 3

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It varies with the region.

"Prime" is how you pronounce it in American English. Here is a nice reference for American English pronounciations of math symbols; $f'$ is on the top of the second page.

"Dash" is how you pronounce it in British English: Here (search for dash).

  • 1
    And apparently the British English one is different :-) http://www.uefap.com/speaking/symbols/symbols.htm (and concurs with what I have been using all my life!)2011-06-24
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    In Israel we use "tag" (read like "tug").2011-06-24
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    Interesting! I hadn't heard of these variations before, I'll keep my ears open for them if I go abroad. You should post them as answers too, they are just as valid :)2011-06-24
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    @Zev: I suppose it might be better if we just edit those into your answer...2011-06-24
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    @Aryabhata: Sounds good, go ahead!2011-06-24
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    @Zev: Done! I didn't do Yuval's as OP specifically asks for English and I am not sure if Isreali English is well-defined. I am also afraid, we could have an explosion of regions...2011-06-24
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    I should have thought before, to make it community wiki. But I have done so now - thus anyone with an addition can make it.2011-06-24
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    It may have been common to pronounce $f'$ as 'f dash' in British English in 1981, but for as long as I've been learning mathematics (including eight years in a British university) I've always called it 'f prime'.2011-06-24
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    @Chris: I agree. "Dash" is better reserved for the en dash and em dash---those useful punctuators that you can't find on your keyboard.2011-06-24
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    At school (in England) we were taught 'f dash', 'f double dash', and so on, but at soon as I got to University (also in England) it became 'f prime'. I haven't heard anyone say 'f dash' in a long time.2011-06-24
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    I concur with Chris and Alex, most people in the immediate vicinity of my [current office](http://www.dpmms.cam.ac.uk/) say it as 'prime', but demographically I cannot claim that most of them are in fact British.2011-06-24
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    I fear the only “double dash” I've been taught in school is Mario Kart.2011-09-02
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$f'\rightarrow$ f prime

$f^{\prime\prime}\rightarrow$ f bis

$f^{\prime\prime\prime}\rightarrow$ f tris

$f^{\prime\ \backprime\prime}\rightarrow$ f tetrakis

However most people do not know these words and just say double prime, triple prime etc.

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    Are these real names? I've done a quick google search but couldn't find any reference to any of these.2013-01-05
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    I don't like this; prime is derived from Latin, whereas the others are from Greek.2013-01-05
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    @-1 Why?, do you think I made this up?2013-01-28
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    Yes, I do (and someone else it seems). All Google references lead to Chemistry stuff. Still, by the benefit of the doubt and because it sounds funny, +1.2013-06-14
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    I agree with f bis, being common in Swedish education. The other's I've never heard, but I haven't seem them used in notation either, f^(n) being the norm.2013-10-18
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In high school and junior-high school in Japan, we read a' as "a dash". However, in universities, it is occasionally read as "a prime" due to American influence.

I am not native speaker of English; therefore, I explored dictionaries and found a description. The Oxford English Dictionary vol. XIII (1970) states that it "usually read as `a dash' " in the explanation of the word "prime". I feel something odd in this statement, but in the explanation of the word "dash" in OED vol. III (1969), I found that "a stroke or line (usually short and straight) made with a pen or like, or resembling one, so made ....". I am now realised the symbol ' should be recognized to be a short script.

I would like rather ask why American reads a" as double prime. Why the prime (= the most important) is not only one?

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    The problem with *dash* is that it's commonly used for a hyphen (`-`). (Not saying that this answer is wrong, but using *dash* will not be widely understood.)2017-02-28
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    The main meaning of "dash" is "a short and rapid run". This perfectly matches the quick writing of a pen for adding ' adjacent to f, even though "prime" is an actual name of the symbol. Of course, I also use "f prime" when nobody understands "f dash". However, I don't feel "f dash" is a minority2017-03-01