A handful of English words behave by rules that have nothing to do with the usual add an -s pattern — and knowing how to pronounce irregular plurals in English is one of those quiet markers that separates a careful speaker from one who sounds uncertain, even when everything else they say is right. Words like criteria, phenomena, and alumni carry their Latin and Greek origins into modern English, and the pronunciation traps they set are sprung dozens of times a day in boardrooms, lectures, and interviews.
This guide covers the most commonly mispronounced irregular plurals, explains the patterns behind them, and gives you the specific sounds to practise. You will come away knowing not just how each word is said, but why — which makes the knowledge stick.
Why These Words Cause Problems
English absorbed an enormous number of words from Latin and Greek, many of them through academic and scientific writing rather than everyday conversation. That means the plural rules — Greek -on becomes -a, Latin -um becomes -a, Latin -us becomes -i — arrived in the language without being taught to most people who use them.
The result is that educated, fluent speakers routinely say a phenomena or these criterias, treating foreign plurals as singulars or adding an unnecessary -s. The errors are understandable. They are also noticeable.
The Main Patterns, With Pronunciation
Greek -on → -a: criterion / criteria, phenomenon / phenomena
This is the pattern responsible for the two most frequently confused pairs in professional English.
Criterion (singular): /kraɪˈtɪə.ri.ən/ — four syllables: cry-TEER-i-un Criteria (plural): /kraɪˈtɪə.ri.ə/ — four syllables: cry-TEER-i-uh
The difference is subtle. The singular ends in a clear -un sound; the plural ends in a soft -uh (the schwa). Practise the contrast by saying this sentence aloud:
"The main criterion is cost; all other criteria are secondary."
Notice where the stress falls — on the second syllable in both words — and notice that the final syllable changes but the rest of the word does not.
Phenomenon (singular): /fɪˈnɒm.ɪ.nɒn/ — fe-NOM-i-non Phenomena (plural): /fɪˈnɒm.ɪ.nə/ — fe-NOM-i-nuh
Again, the stress stays on the second syllable throughout. The plural softens the final syllable into a schwa. A sentence to say aloud:
"Each phenomenon was recorded separately; taken together, the phenomena suggest a pattern."
The error to avoid: "This is an interesting phenomena." Using the plural as a singular is the most common mistake with this word, and it tends to catch the ear of anyone who knows the difference.
Latin -um → -a: datum / data, medium / media, curriculum / curricula
Data is probably the most contested word on this list. Strictly, datum is the singular and data the plural, which would make the data show the technically correct form. In scientific and academic presentations, this plural treatment still holds and is worth using. In everyday professional speech, the data shows is so widespread that it rarely raises an eyebrow.
What matters for pronunciation is this: data is /ˈdeɪ.tə/ — DAY-tuh, not DAH-tuh. The DAH variant exists and is used, but the DAY pronunciation is standard in British English.
Medium / media follows the same -um / -a pattern.
- Medium: /ˈmiː.di.əm/ — MEE-di-um
- Media: /ˈmiː.di.ə/ — MEE-di-uh
Social media has made the word media so familiar that its plural nature is often forgotten. Saying the media is versus the media are is a stylistic choice; saying a media is simply an error.
Curriculum / curricula appears in job applications and education discussions constantly.
- Curriculum: /kəˈrɪk.jʊ.ləm/ — kuh-RIK-yoo-lum
- Curricula: /kəˈrɪk.jʊ.lə/ — kuh-RIK-yoo-luh
The plural again ends in a soft schwa. A sentence worth saying aloud:
"Each school designs its own curriculum, but the curricula across the region share common features."
Latin -us → -i: alumnus / alumni, syllabus / syllabi, cactus / cacti
This pattern produces the -eye ending that surprises many speakers who expect -ee.
Alumnus (singular male or gender-neutral): /əˈlʌm.nəs/ — uh-LUM-nus Alumni (plural): /əˈlʌm.naɪ/ — uh-LUM-nye
The final syllable rhymes with eye or sky, not with me or free. This is one of the more frequently mispronounced words in English, particularly at graduation ceremonies and alumni events, where getting it right would be most appropriate.
There is also the feminine form: alumnae /əˈlʌm.niː/ — uh-LUM-nee — used for groups of women. In mixed or gender-unspecified groups, alumni is standard.
Syllabus / syllabi: /ˈsɪl.ə.bəs/ → /ˈsɪl.ə.baɪ/ — SIL-uh-bus → SIL-uh-bye. (Note: syllabuses is also accepted and widely used.)
Cactus / cacti: /ˈkæk.təs/ → /ˈkæk.taɪ/ — KAK-tus → KAK-tie. (Cactuses is equally correct in non-botanical contexts.)
Greek -is → -es: analysis / analyses, thesis / theses, crisis / crises
Here the change is not just in spelling but in which syllable carries the stress.
Analysis: /əˈnæl.ɪ.sɪs/ — stress on the second syllable: uh-NAL-i-sis Analyses: /əˈnæl.ɪ.siːz/ — stress still on the second syllable: uh-NAL-i-seez
Thesis: /ˈθiː.sɪs/ — stress on the first syllable: THEE-sis Theses: /ˈθiː.siːz/ — stress stays first: THEE-seez
Crisis: /ˈkraɪ.sɪs/ — CRY-sis Crises: /ˈkraɪ.siːz/ — CRY-seez
The pattern is consistent: the -is ending becomes -eez. A sentence for the pair you are most likely to use:
"The first analysis was inconclusive, but all three analyses pointed in the same direction."
A Note on Acceptable Change
Language is not fixed, and some of these distinctions are loosening. Criterion and phenomenon used as plurals appear often enough in print that some dictionaries now note them as informal alternatives. Syllabuses and cactuses are fully standard.
None of that means you should ignore the traditional forms. Knowing them gives you a choice. In a technical presentation, a job interview, or any setting where precision carries weight, using criteria correctly and pronouncing alumni as uh-LUM-nye will mark you as someone who pays attention to language — and that is rarely a disadvantage. The way you speak signals how carefully you think, a point worth bearing in mind whenever you want to be taken seriously. You can read more about this on the ummute benefits page.
Practising What You Have Learned
The most effective way to consolidate these is not to memorise a list but to use each word in a sentence you would naturally say. Take the words relevant to your work or field and build two sentences for each: one with the singular, one with the plural. Say them aloud slowly, then at normal pace. Record yourself if you can — the ear catches things the eye misses.
If you want feedback on whether your pronunciation of these words actually lands as intended, see how ummute works. Hearing yourself analysed in real time is considerably faster than waiting for someone to politely tell you that you have been saying phenomenas for the past three years.
The words covered here — criteria, phenomena, alumni, analyses and the rest — are not rare or specialist vocabulary. They appear in everyday professional speech, and the people in the room almost certainly notice when they are mishandled. The good news is that the patterns are learnable in an afternoon, and once you have them, they stay with you.