I study mathematics and as I'm sure you can imagine, often read the word formula. I also quite often come across formulas used as the plural. This always annoys me as I was under the impression that the correct plural of formula was formulae?

Is there any consensus or information as to why there is two (seemingly) accepted forms of this? I thought that formulae probably has a Latin derivation and formulas may be Americanized?

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    I would advise checking the journal where one expects to have one’s work published to see which convention they follow. – tchrist Aug 3 '14 at 12:37
  • @tchrist I was more just interested. I think I will stubbornly stick my archaic ways and use formulae! – hmmmm Aug 3 '14 at 12:51
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    I don’t know why you write Americanized when you mean naturalized. You seem to associate “Americanize” with the idea of doing something you don’t like, as though it were bastardize instead. That isn’t very constructive. In any event, sometimes one has two different plurals in play with slightly different meanings or registers, as occurs with index supporting indices in technical contexts and indexes in non-technical ones. – tchrist Aug 3 '14 at 12:52
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    Related: Which style of Latin plurals should I use? Actually expressly covers formulas vs. formulae, too. – RegDwigнt Aug 3 '14 at 13:54
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    An NGram of usage over the past half-century confirms my expectation that the irregular formulae continues to lose ground. So go for formulas unless you're constrained by some style guide, editor, educational establishment, or whatever. – FumbleFingers Aug 3 '14 at 15:20

It appears that the plural formulas has become the most common term also in scientific context:

for·mu·la /ˈfɔːmjʊlə/: - n. pl. for·mu·las or for·mu·lae.

Usage note:

  • The word formula has two possible plural forms, formulae and formulas. The traditional distinction is that formulas should be used in general writing and formulae in mathematical and scientific contexts, but analysis of the Oxford English Corpus shows that formulas is increasingly the dominant form in both technical and general uses. (ODO)

Ngram and Ngram: the graphs suggest that the most common use is 'formulas'.

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