Types of irregular plural
There are many types of irregular plural, but these are the most common:
Noun type
Ends with -fe
Ends with -f
Forming the plural
Example
Change f to v
knife
then
life
Add -s
wife
wives
Change f to v
half
halves
then
wolf
wolves
Add -es
loaf
loaves
knives
lives
potato
Ends with -o
Add -es
potatoes
tomato
tomatoes
volcano
volcanoes
cactus
ends with -us
Change -us to -i
cacti
nucleus
nuclei
focus
foci
analysis
ends with -is
Change -is to -es
analyses
crisis
crises
thesis
ends with -on
Change -on to -a
Change the vowel
or
ALL KINDS
Change the word
or
Add a different ending
Unchanging
Singular and plural
are the same
theses
phenomenon
criterion
criteria
man
men
foot
feet
child
person
tooth
mouse
phenomena
children
people
teeth
mice
sheep
deer
fish (sometimes)