Words Ending in -a: Formulae or Formulas?
Quick Answer
Latin words ending in -a have a formal plural in -ae: one formula, two formulae. In everyday English, the simple -as form is equally correct — and far more common.
See the Pattern First
Most of these words have two accepted plurals. Context decides.
- In maths class: two formulae. In a shop: two baby formulas.
- An insect has two antennae. A radio has two antennas.
- The back has many vertebrae — here the Latin form is normal.
- Society attaches stigmas to illness — here the English form is normal.
See what is happening? The -ae form survives in science and medicine. The -as form takes over in everyday life. Same word, different room.
The Full List
The form in bold is the one you are most likely to need.
| One | Many | One | Many |
|---|---|---|---|
| antenna | antennae / antennas | dogma | dogmas |
| formula | formulas / formulae | nebula | nebulae |
| schema | schemas / schemata | stigma | stigmas |
| vertebra | vertebrae | larva | larvae |
These come up often, so they have their own full lesson with more practice: the plural of larva.
Which One Should You Actually Use?
Ask yourself one question: am I writing about science? If yes, use -ae — biologists write larvae, nebulae, vertebrae, and nothing else looks right to them.
If you are writing anything else — an email, an essay about society, a shopping list — use -as. “Formulas”, “dogmas” and “stigmas” are completely standard and will never be marked wrong.
Science: -ae. Everyday life: -as.
One Word With Three Forms
Schema is unusual — it is Greek, not Latin, so it has an extra option:
- schemas — normal in computing and psychology.
- schemata — the Greek form, used in academic philosophy.
If you work with databases, “schemas” is what everyone says. Do not switch to “schemata” to sound clever.
Mistakes Learners Make (You Are Not Alone)
The real mistake here is not choosing the wrong ending — it is treating a plural as a singular:
- ✗ this larvae is small → ✓ this larva is small (one larva, many larvae)
- ✗ a vertebrae in my back → ✓ a vertebra in my back (“a” needs the singular)
- ✗ two antennaes → ✓ two antennae (do not add -s on top of -ae)
Because -ae does not look like a plural to English eyes, people use it for one thing. Remember: if it ends in -ae, there is more than one.
Your Turn — Quick Quiz
Five questions. Take your time — the table above is still there if you need it.
1. 1. The biologist counted the mosquito ____ in the water.
2. 2. In everyday English, the plural of “formula” is usually:
3. 3. Which sentence is CORRECT?
4. 4. The database has three different ____.
5. 5. Telescopes photograph distant ____.
Keep Going
You can now pick the right form for the situation instead of guessing.
One more Latin group is waiting, and it produces the strangest-looking plural in English. One index, two indices. One vortex, two vortices. Where does that “-ices” come from?
Next lesson: Words ending in -x: index, appendix, vortex
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.
