# What do I call the ′ in mathematical formulae?

As in `x′ = x + t`

"Ex (?) equals ex plus tee".

In Russian it is called "штрих" (shtrikch).

• Interesting: your word is German, strich (pronounced /ʃtrix/), "line,stroke". – StoneyB on hiatus Jan 7 '15 at 23:50
• Related: ell.stackexchange.com/q/43012/3281. – Damkerng T. Jan 8 '15 at 0:51
• @StoneyB, It means the same thing in Russian. – Vi. Jan 8 '15 at 1:23
• Just voted to leave open as the related question only states how to prononce it if representing a derivative. This question is more general. – Stephie Jan 8 '15 at 21:00

The single tick following a variable is often (but not always) used to represent a derivative and (in the United States) is always pronounced "prime." In your example, "Ex prime = ex plus tee."

f(x) = x² <--- "Eff of ex equals ex squared."

f′(x) = 2 x <---- "Eff prime of ex equals two ex."

f′′(x) = 2 <---- "Eff double prime of ex equals two."

In non-mathematical contexts it is called a single quote (or a "tick"). This wikipedia entry differentiates between the prime symbol and the single quote. As they also note, using a single quote (') as a stand-in for prime (′) is not uncommon. Thanks Vi for the link.

I have learned from other respondents that in the UK, Canada and Australia, it is pronounced prime unless it signals a derivative, in which case it can be pronounced dash.

In case you run into these two:

is pronounced "ex bar"

is pronounced "ex hat"

• ′ if you want it. Also ″ and ‴ as long as I’m here. – Tyler James Young Jan 8 '15 at 0:10
• Found a source: en.wikipedia.org/wiki/Prime_%28symbol%29 – Vi. Jan 8 '15 at 1:22
• is "ex nihilo" – Ben Jackson Jan 8 '15 at 5:52
• It's probably worth mentioning that people do also say "derivative of x" and "second derivative of x" rather than "x prime" and "x double-prime". That's not pronouncing the symbol so much as stating what the symbol means, but it still is worth noting. – KRyan Jan 8 '15 at 19:31

In my experience, in the specific case where it indicates a derivative, it is pronounced "dash". Odd, I know, as it does not look anything like a dash "-".

In all other circumstances, "prime".

Found this nice general reference on mathematical and scientific symbols pronunciation that may be useful.

• +1 Where do you hear "dash" used for derivative? I have never heard that directly, but I have heard other people say that that they knew someone who said it....Don't know where those third parties were from though. In math and engineering graduate school in Wisconsin, Oregon and Washington, I only heard prime. – Adam Jan 8 '15 at 5:21
• @Adam This is my experience in the UK and Australia. Maybe a UK/US thing? – Keith Jan 8 '15 at 5:28
• As long as they don't call it a hyphen? – a CVn Jan 8 '15 at 8:38
• Growing up in Ireland (which is obviously a very similar experience to England), I also learnt "f dash x" for a derivative, and prime for all other circumstances, so yes, it is probably a UK vs. US thing. – Mark Allen Jan 8 '15 at 14:36

In High School and Junior High in Japan, we read `a′` as "a dash."

However, in universities, it is occasionally read as "a prime" due to American influence.

The Oxford English Dictionary (1969) states that it is "usually read as 'a dash' in the explanation of the word 'prime'."