Words Ending in -a: Formulae or Formulas?
Quick answer
Learn the plural of each noun ending in -a. Some have more than one accepted plural: formula → formulas or formulae, and schema → schemas or schemata. There is no single rule that changes every final -a to -ae.
Useful Forms to Recognise
- formula: formulas or formulae
- schema: schemas or schemata
- nebula: nebulae or nebulas
- antenna: antennae is usual for insect feelers; antennas is usual for radio equipment
- vertebra: vertebrae is a common plural
- larva: larvae is a common plural
- dogma: dogmas is a common plural
- stigma: stigmas is common when discussing social attitudes
Some of these nouns have additional specialised or less common forms. A dictionary can show the forms and meanings for the particular word you need. The list is a practical introduction, not an exhaustive account of every variant.
Choose by Word and Meaning
Do not use “science = -ae, everyday English = -as” as a rule. Scientific writing uses accepted forms for each word and may follow a publication’s preferred style. For example, both nebulas and nebulae can name clouds of gas or dust in space.
Likewise, schemas and schemata are both valid plurals. A particular field or writer may prefer one, but the other form is not automatically a grammar error. Formula also has two established plurals: formulas and formulae.
Keep Singular and Plural Separate
- One: This larva is small. More than one: These larvae are small.
- One: I broke a vertebra. More than one: The diagram shows several vertebrae.
- Do not add another plural ending to a form that is already plural: two antennae, not two antennaes.
In the examples above, the -ae form is plural. This is a pattern in the listed nouns, not a spelling test that identifies the number of every word in English.
For more examples of one young insect and several young insects, read the plural of larva.
Practise Accepted Alternatives
The quiz sometimes offers a pair of accepted forms as one answer. This lets you learn alternatives without being marked wrong for choosing a valid plural. Check whether a sentence needs one thing or more than one before choosing an ending.
Your Turn — Quick Quiz
Five questions. Take your time — the table above is still there if you need it.
1. The biologist found one mosquito ____.
2. Which pair contains two accepted plurals of formula?
3. Which sentence is CORRECT?
4. Which pair contains two accepted plurals of schema?
5. Which pair contains two accepted plurals of nebula?
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
Further reference: Merriam-Webster: schema.
Further reference: Merriam-Webster: nebula.
Further reference: Merriam-Webster: formula.
I’m Khamis Maiouf. I’m studying Health and Social Care and have completed Functional Skills Level 2 in English and Level 3 Hairdressing. I have taught ESOL in my community and helped students with GCSE English. I run English Teacher Site to help people learn and practise English.