Greek and Latin Plurals: How "Analyses" and "Criteria" Actually Sound

Here is the rule most textbooks skip. When an English word borrowed from Greek or Latin forms its plural by changing its ending, the sound changes too, and often in a way the spelling does not predict. The single most useful piece: words ending in -is change to -es, and that -es is pronounced /iz/, a long ee sound plus z, not the /ɪz/ of ordinary English plurals like buses. The stress stays exactly where it was in the singular.

So analysis /əˈnæləsɪs/ becomes analyses /əˈnæləsiz/. Same stress, same rhythm, and only the final syllable changes from a short, weak /sɪs/ to a long, clear /siz/. Get that one contrast right and you fix a dozen academic words at once.

Group A: -is Becomes -es, Pronounced /iz/

These are the words you meet in essays, lab reports, and business presentations. Say the singular, then swap the last syllable.

• crisis /ˈkraɪsɪs/ becomes crises /ˈkraɪsiz/
• thesis /ˈθisɪs/ becomes theses /ˈθisiz/
• hypothesis /haɪˈpɑθəsɪs/ becomes hypotheses /haɪˈpɑθəsiz/
• parenthesis /pəˈrenθəsɪs/ becomes parentheses /pəˈrenθəsiz/
• diagnosis /ˌdaɪəɡˈnoʊsɪs/ becomes diagnoses /ˌdaɪəɡˈnoʊsiz/

The "Bases" Trap

One spelling, two words, two pronunciations. Bases as the plural of basis is /ˈbeɪsiz/, with the long ee. Bases as the plural of base (a baseball base, a military base) is /ˈbeɪsɪz/, with the ordinary weak plural ending. Context tells the listener which one you mean, but only if you make the vowel difference audible. Practice the pair: "on several bases" (the reasons) versus "three bases loaded" (the objects).

A second thing worth noticing in this group is that the singular ending is genuinely weak. In analysis, the last syllable is unstressed and the vowel reduces almost to nothing, so the word ends quietly. In analyses, that same position carries a full, tense vowel, which makes the ending sound longer and slightly heavier even though the stress has not moved. Learners who try to signal the plural by shifting the stress instead of lengthening the vowel end up with a word that native speakers hear as a mistake. Keep the beat identical and change only the final vowel quality.

Group B: The Latin Endings

Latin borrowings change endings in three main patterns, and each carries its own sound.

-um and -on Become -a

The plural ending here is a plain, unstressed schwa /ə/. Nothing dramatic happens to the stress.

• datum /ˈdeɪtəm/ becomes data /ˈdeɪtə/
• medium /ˈmidiəm/ becomes media /ˈmidiə/
• curriculum /kəˈrɪkjələm/ becomes curricula /kəˈrɪkjələ/
• bacterium /bækˈtɪriəm/ becomes bacteria /bækˈtɪriə/
• criterion /kraɪˈtɪriən/ becomes criteria /kraɪˈtɪriə/
• phenomenon /fəˈnɑmənɑn/ becomes phenomena /fəˈnɑmənə/

-us Becomes -i, Pronounced /aɪ/

This is the one learners most often mispronounce, because the letter i looks like it should be /i/. In American English it is the diphthong /aɪ/, the sound in eye.

• fungus /ˈfʌŋɡəs/ becomes fungi /ˈfʌndʒaɪ/
• cactus /ˈkæktəs/ becomes cacti /ˈkæktaɪ/
• alumnus /əˈlʌmnəs/ becomes alumni /əˈlʌmnaɪ/
• radius /ˈreɪdiəs/ becomes radii /ˈreɪdiaɪ/
• nucleus /ˈnukliəs/ becomes nuclei /ˈnukliaɪ/

Note that fungi also changes its consonant: the hard /ɡ/ of fungus softens to /dʒ/ before the i. If you want the full story on when g after n is hard, soft, or silent, see our guide to the NG rule in English.

-a Becomes -ae, and -ix or -ex Becomes -ices

The -ae ending is /i/ in American English: formula /ˈfɔrmjələ/ becomes formulae /ˈfɔrmjəli/. The -ices ending is the interesting one, because the stress moves and the vowel in the stem reduces: index /ˈɪndeks/ becomes indices /ˈɪndəsiz/, where the clear /e/ of the second syllable collapses to a schwa.

The Full Table

The Grammar Mistake People Hear Immediately

Because these plurals do not end in s, learners often treat them as singular. Native listeners notice instantly. Remember:

• criteria is plural. Say "one criterion," never "a criteria."
• phenomena is plural. Say "a strange phenomenon," never "a phenomena."
• bacteria is plural. "These bacteria are resistant," not "this bacteria is."
• media is plural in academic writing, though "the media is" is now widely accepted in everyday speech about the press.

Exceptions: When Regular English Plurals Win

Many of these words have been in English long enough to take normal -s or -es plurals in ordinary speech, and using the classical form can sound stiff. All of the following are standard:

• forums rather than fora
• stadiums rather than stadia
• syllabuses rather than syllabi
• cactuses alongside cacti
• appendixes for the body part, appendices for sections of a book
• formulas in everyday use, formulae in mathematics

Data deserves its own note. Technically the plural of datum, it now functions as a mass noun for most speakers, so "the data is clear" is completely normal in American English. "The data are clear" is still preferred in formal scientific writing. Both are defensible; just be consistent.

Practice These Words

Say It Out Loud

Read these three sentences twice, slowly and then at speed.

1. "Our analyses of the two crises rest on different hypotheses."
2. "The criteria are clear, but the data is incomplete and the phenomena are hard to measure."
3. "The alumni collected fungi, cacti, and antennae for the museum's appendices."

The single habit that fixes most of these words is lengthening that final /iz/. Say analysis, then analyses, and exaggerate the ee until you can hear the difference at conversation speed. To keep sharpening the long and short vowel contrast that underlies this rule, work through our vowel practice exercises.