>
As a general rule, the plural is formed by adding "-s" to
the singular form of nouns.
shoe --> shoes | book --> books | river --> rivers
>
Nouns ending in "s" or "s" will generally take
the ending "-es" :
bus --> buses | kiss --> kisses
>
Words ending in "y" will generally take the ending "-ies"
in place of the "y":
party --> parties | supply --> supplies
>
A few words have very irregular forms in the plural:
one man --> two men
one woman --> two women
one person --> two people
one foot --> two feet
one mouse --> two mice
one goose --> two geese
one tooth --> two teeth
one wife --> two wives
one child --> two children
one knife --> two knives
one thief --> two thieves
one dwarf --> two dwarves (or: dwarfs)
one potato --> two potatoes
one leaf --> two leaves
one life --> two lives
one loaf --> two loaves
one half --> two halves
>
A small set of words do not change form in the plural:
one moose --> two moose
one sheep --> two sheep
one aircraft --> two aircraft
> Words of Greek or Latin origin which have
retained their original endings will generally take the plural form
associated with the language they are drawn from:
one alumnus --> two alumni
one syllabus --> two syllabi
one alumna --> two alumnae
one alga --> many algae
one criterion --> many criteria
one forum --> many fora (or : forums)
one thesis --> two theses
one hypothesis --> two hypotheses
one phenomenon --> two phenomena
one cactus --> two cacti (or : cactuses)
one diagnosis --> two diagnoses
one oasis --> two oases
one analysis --> two analyses
>
A few nouns are invariable or collective, always indicating a plural
meaning:
She gave me some information.
Michelle has a lot of clothes.
Plurals (来源：英语交友 http://friends.englishcn.com)