For example, I have one function called f. Now I make some change to f and create a new function called f'. But how do native people read the "f'"? Like "f apostrophe"?

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    I'm voting to close this question as off-topic because this is really a question of mathematics.
    – David M
    Oct 23 '19 at 4:25
  • I always call it “f-off”.
    – David
    Oct 23 '19 at 8:38
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    It's often read as "f-dashed". The punctuation mark, by the way, is not an apostrophe. It is always a straight line, whereas in many fonts an apostrophe is curved.
    – Rosie F
    Oct 23 '19 at 8:38
  • Ususally, marks like this aren't one-offs. They are used in a consistent manner throughout a paper. When read, they are decoded as to what operation they represent. In describing the notation, you would say "we write f prime to represent ...". But if f' is the derivative of f, I would read f' as f derivative. If it is a nondimentionalized f, I would read it as nondimentional f, etc.
    – Phil Sweet
    Oct 23 '19 at 10:45
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    Possible duplicate of Which do you read x' as dash or prime? Nov 5 '19 at 17:51

Mathematician here. We pronounce f' as "f prime".

(Addendum: native English speaker in the United States. So, "we" refers to that group.)

From Wikipedia: "In mathematics, the prime is generally used to generate more variable names for things which are similar, without resorting to subscripts – x′ generally means something related to or derived from x."


  • Not always. 'F dash' is a reasonably common alternative. Though 'dash' has the disadvantage here of being distinct from the usual punctuation marks, it has the advantage over 'prime' that it is not used in distinct ways in maths, which multiple usage could lead to confusion. Nov 5 '19 at 17:49
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    This may be a cultural/nationality thing. I have personally never used/heard "dash" in this context. Nov 5 '19 at 17:59
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    @EdwinAshworth I was a math minor in college, and have always heard this as "f prime." And while you're right that it can also mean "derivative of f," the notiation is the same for both (f') so pronouncing it differently out loud won't fix the problem. Nov 5 '19 at 19:18
  • @Pluto the Planet I taught maths to Oxbridge entrance level (and also covered remedial maths), and had to be aware of negotiating conflicting senses both intramaths ('similar', 'function') and intermaths ('function' again, 'prime'). We always used f-dash-x, as I had experienced in grammar school, while being aware of the alternative. But the non-incorrectness of both has already been covered here at the earlier thread (which should have been shuffled over to MathsSE anyway). See Colin Fine's statement. / 'Mathematician here. We pronounce ...' sounds dictatorial. Nov 6 '19 at 16:41
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    @EdwinAshworth: Duly noted. I edited the answer to state my context as US native English. Nov 6 '19 at 16:59

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