Words Ending in -um and -on: Curriculum → Curricula
Quick Answer
Words from Latin ending in -um and Greek words ending in -on change the ending to -a: one curriculum, two curricula; one phenomenon, two phenomena.
See the Pattern First
Four sentences. Watch the ending change from -um or -on to -a.
- The school changed one curriculum. It changed both curricula.
- That is a strange phenomenon. Those are strange phenomena.
- She sent one memorandum. He filed all the memoranda.
- There is an error — one erratum. The book lists many errata.
This group is beautifully consistent. Unlike the -us words, there are almost no arguments here: the -a form is the standard one in careful writing.
The Full List — 10 Words
These appear in school, work and formal documents.
| One | Many | One | Many |
|---|---|---|---|
| addendum | addenda | colloquium | colloquia |
| curriculum | curricula | erratum | errata |
| memorandum | memoranda | phenomenon | phenomena |
| referendum | referenda | spectrum | spectra |
| stratum | strata | symposium | symposia |
Why the -a Ending Feels Strange in English
English speakers expect a plural to sound bigger than a singular — “cat” becomes “cats”. Here the word actually gets shorter: “curriculum” becomes “curricula”. That is why it feels wrong even when it is right.
A useful check: if you can put “the” and “are” around it, use the -a form. “The data are clear.” “The phenomena are rare.” If it needs “is”, you want the singular.
-um and -on both become -a.
Two Softer Ones
English is relaxing about two of these, and both forms are now accepted:
- referendum → referenda or referendums — newspapers use both.
- symposium → symposia or symposiums.
For the other eight, stay with the -a form in any formal writing.
Mistakes Learners Make (You Are Not Alone)
The classic error in this group is treating the plural as a singular:
- ✗ this criteria is → ✓ this criterion is (one criterion, many criteria)
- ✗ a phenomena happened → ✓ a phenomenon happened (“a” needs the singular)
- ✗ two curriculums → ✓ two curricula (curricula is standard in education)
Even careful writers slip on “phenomena”. If you remember that it is already plural, you are ahead of most people.
Your Turn — Quick Quiz
Five questions. Take your time — the table above is still there if you need it.
1. 1. The school updated both ____ this year.
2. 2. Scientists study rare natural ____.
3. 3. The report had a list of ____ at the back.
4. 4. Which sentence is CORRECT?
5. 5. The rock has several visible ____.
Keep Going
That is another whole group handled with one rule, and this one has almost no exceptions.
Now here is a strange thought. Some English words never change at all. One sheep, two sheep. One deer, two deer. Why do those words get to ignore every rule you have learned?
Next lesson: Words that look the same in singular and plural
Sources
I’m Khamis Maiouf. English is not my first language – I learned it as an adult in the UK, passed Functional Skills Level 2 in English, qualified in Hairdressing at Level 3, and I’m now studying Business at university. For over five years I’ve taught ESOL classes in my community and tutored students through GCSE English. I write every lesson on this site myself, for the learner I used to be.
