Most English nouns are count nouns. They refer to objects which are thought of as separate and distinct entities, and they have both singular and plural forms. Generally speaking, their plurals are formed in a regular and predictable way. Usually, plurals are formed by adding -s to the singular, or unmarked form of the noun. Nouns that end in -s, -z, -ch, -sh, and -x are made plural by adding an -es.
e.g. inch : inches
box : boxes
dish : dishes

Irregular Plural Formation
The plurals of some count nouns are formed in irregular ways. Here are the rules for forming irregular plurals: (Foreign nouns refer to nouns adopted from Latin or Greek.)

Some nouns that end in -o: take -es
e.g. tomato : tomatoes

Nouns that end in a consonant + -y: change the -y to -i and add -es
e.g. butterfly : butterflies

Nouns that end in -f or -fe: change the -f to -v and add -es
e.g. calf : calves

Nouns that change the vowel but add no ending
e.g. tooth : teeth, mouse : mice

Nouns that show no difference between singular and plural
e.g. deer : deer, fish : fish

Foreign nouns that end in -us: change to -i
e.g. alumnus : alumni, focus : foci

Foreign nouns that end in -a: change to -ae
e.g. formula : formulae, vertebra : vertebrae

Foreign nouns that end in -um: change to -a
e.g. curriculum : curricula, stratum : strata

Foreign nouns that end in -ex or -ix: change to -ices
e.g. index : indices, appendix : appendices

Foreign nouns that end in -is: change to -es
e.g. neurosis : neuroses, thesis : theses

Foreign nouns that end in -on: change to -a
e.g. phenomenon : phenomena, criterion : criteria

 
Raghad,

Thank you Raghad, for this useful information , that we need to review them as much as we contact with language.

Raghad

 
Raghad,
important information and topic as usual
the most thing that I love in your explanation, is your gradual steps which you follow in order to fix the information

My best regards Raghooooodie

 
NOOR TALEB, Ranaa,
Thank you for your participation