| Singular | Plural | Singular | Plural |
| crisis | crises | stratum | strata |
| thesis | theses | radius | radii |
| hypothesis | hypotheses | parenthesis | parentheses |
| focus | foci | synopsis | synopses |
| datum | data | basis | bases |
| alumnus | alumni | automaton | automata |
| alumna | alumnae | analysis | analyses |
| oasis | oases | nucleus | nuclei |
| axis | axes | phenomenon | phenomena |
| genus | genera |
Some words admit of two plurals, one the foreign plural, and one the regular English plural; as,
| Singular | Plural | |
| beau | beaux | beaus |
| formula | formulae | formulas |
| vertex | vertices | vertexes |
| index | indices | indexes |
| cherub | cherubim | cherubs |
| seraph | seraphim | seraphs |
| bandit | banditti | bandits |
Consult a dictionary to see whether there is any difference of meaning between the two plurals of these words.
Exercise 36—The Formation of Participles
| Rap, rapping, rapped | Reap, reaping, reaped |
Rap is a monosyllable ending in a single consonant preceded by a single vowel. The final consonant in such words is doubled before a suffix beginning with a vowel is added.
In reap the final consonant is not doubled because it is preceded by two vowels.
Make the participles of the following verbs:
| chat | lap | suit | step |
| cheat | leap | sit | steep |
| rot | train | sop | trot |
| root | trim | soap | treat |