Writing Tips >> Irregular plurals
Irregular plurals are often seen in scientific writing. When a noun is made plural by changing or keeping its spelling rather than attaching an inflectional suffix (i.e. -s or -es), the plural noun is considered irregular. Irregular plurals usually have Greek or Latin origins.
Some nouns change the spelling when becoming plural. The following table shows examples of irregular plurals which change in different ways morphologically.
| Change | Singular | Plural | Change | Singular | Plural |
| -ex -ices | index | indices | -on -a | criterion | criteria |
| vertex | vertices | phenomenon | phenomena | ||
| -is -es | analysis | analyses | -um -a | medium | media |
| axis | axes | quantum | quanta | ||
| basis | bases | spectrum | spectra | ||
| diagnosis | diagnoses | stratum | strata | ||
| synthesis | syntheses | -us -i | locus | loci | |
| thesis | theses | nucleus | nuclei | ||
| -ix -ices | appendix | appendices | radius | radii | |
| matrix | matrices | stimulus | stimuli |
Some nouns do not change the form when becoming plural. Two examples are shown below.
| Singular | Plural |
| series | series |
| species | species |
In addition to changing or keeping the spelling, a noun may have two acceptable plural forms – an irregular plural and a regular plural. Below are some examples.
| Singular | Irregular Plural | Regular Plural |
| apparatus | apparatus | apparatuses |
| focus | foci | focuses |
| formula | formulae | formulas |
| schema | schemata | schemas |
To ascertain the correct forms of irregular plurals, dictionaries should be consulted.
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