Vertebrae, bacteria and cacti: Forming plurals in English 2

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by Liz Walter

Last month I looked at the basic rules for forming plurals in English . In this post, I look at some more complex cases, where the words come from Latin and Greek.

A large proportion of English words have Latin or Greek roots. We still use the Latin plurals for many words, particularly in scientific language, although it is acceptable to use English plurals (usually with ‘s’ or ‘es’) for some of them, particularly non-technical words such as stadium or cactus. However, this depends on the English plural being simple to pronounce – the plural of crisis is always crises, probably because ‘crisises’ is so difficult to say.

Common Latin plurals include words ending in ‘us’ which form their plural with ‘i’, e.g. cacti, stimuli, radii, fungi, alumni and words ending in ‘um’ which form their plurals with ‘a’, e.g. bacteria, data, millennia, auditoria. Words ending in ‘a’ sometimes form their plurals with ‘ae’, e.g. formulae, larvae, vertebrae, antennae.

Words ending in ‘ix’ drop the ‘x’ and add ‘ces’, e.g. matrices, appendices, while those ending in ‘ex’ often drop ‘ex’ and add ‘ices’, e.g. indices, vortices, apices. Not surprisingly, some of these plurals are becoming increasingly rare, and it is common and acceptable to use e.g. matrixes, apexes, vortexes.

Greek-origin words ending in ‘is’ often form their plural with ‘es’, e.g. bases, ellipses, neuroses, synopses.

As I mentioned before, some words – particularly common, non-technical words – are increasingly heard with regular English plural forms. Which plural you choose will probably depend on how formal you want to be. For instance, it would sound pretty odd to say termini or aquaria in informal speech, whereas formulae and matrices are quite normal in scientific texts.

One of the problems with insisting on Latin rules is that you have to have a reasonable knowledge of etymology (where words come from) and many word pedants are themselves inconsistent. Two words which cause a lot of debate are data and media. Both plurals in Latin, many people treat them as singular in English, coming up with phrases such as ‘the data is convincing’ or ‘the media is biased’. However, even purists who deplore this usually accept agenda and stamina as singular nouns, even though they too are plural in Latin.

Another danger comes with trying to make rules based on spelling only. For instance people sometimes ask why we don’t say octopi and omnibi – the reason for the former is that ‘octopus’ is a Greek, not a Latin word, and for the latter that ‘omnibus’ is a dative plural (of omnis), so it makes no grammatical sense to add a plural ending to it.

I’m sorry if all of this is a bit complicated, but remember, if you are in any doubt about how to form a plural, you can consult a dictionary such as the one on this site.

8 thoughts on “Vertebrae, bacteria and cacti: Forming plurals in English 2


    Would it take a genius to know the plural of “genus”? Would someone be an ignoramus if they didn’t know? Would only genii say “genera” (as a Latin third-declension noun) and ignoramuses say “geni”? (Not “ignorami”, of course, because “ignoramus” is not a Latin singular first-declension noun but actually the name of a character from a 16th-century English play, based on a Latin first-person plural verb.) Or, after these words being part of English for centuries, can we stop having to learn Latin grammar just to speak English? Just another one of the language’s many conundr…

  2. João Bosco

    Amazing this text. Portuguese is my native language which, as you know, comes from Latin, and because of this it is easy for us to understand these plural rules. I am surprised. I didn’t know this way to form plural in English. Congratulations.

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