# How do you pronounce the symbol $'$ in $f'$?

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!

• 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... Commented Jun 24, 2011 at 6:03
• 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". Commented Jun 25, 2011 at 22:09
• Strictly speaking, the prime (′) is a different character from the apostrophe (').
– user856
Commented Sep 2, 2011 at 9:04
• I would also read it as f prime.
– user12205
Commented Sep 2, 2011 at 11:44
• @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)!
– user856
Commented Sep 2, 2011 at 12:02

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).

• And apparently the British English one is different :-) uefap.com/speaking/symbols/symbols.htm (and concurs with what I have been using all my life!) Commented Jun 24, 2011 at 6:07
• In Israel we use "tag" (read like "tug"). Commented Jun 24, 2011 at 6:08
• 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'. Commented Jun 24, 2011 at 8:08
• @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. Commented Jun 24, 2011 at 8:24
• 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.
– Alex
Commented Jun 24, 2011 at 12:14

$f'\rightarrow$ 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.

• Are these real names? I've done a quick google search but couldn't find any reference to any of these. Commented Jan 5, 2013 at 15:16
• I don't like this; prime is derived from Latin, whereas the others are from Greek. Commented Jan 5, 2013 at 15:17
• @-1 Why?, do you think I made this up? Commented Jan 28, 2013 at 14:13
• 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. Commented Jun 14, 2013 at 16:02
• 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. Commented Oct 18, 2013 at 15:26

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?

• 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.) Commented Feb 28, 2017 at 11:16
• 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 minority Commented Mar 1, 2017 at 8:05