English countable nouns have two numbers — the singular and the plural.
The main types of the plural forms of English nouns are as follows:
I. 1. The general rule for forming the plural of English nouns is by adding the ending ‑s (-es) to the singular; ‑s is pronounced in different ways:
[Iz] after sibilants: noses, horses, bridges.
[z] after voiced consonants other than sibilants and after vowels: flowers, beds, doves, bees, boys.
[s] after voiceless consonants other than sibilants: caps, books, hats, cliffs.
2.If the noun ends in ‑s, ‑ss, ‑x, ‑sh, ‑ch, or ‑tch, the plural is formed by adding ‑es to the singular:
bus — buses
box — boxes
bench — benches
glass — glasses
brush — brushes
match — matches
3. If the noun ends in ‑y preceded by a consonant, ó is changed into i before ‑es.
fly — flies
army — armies
lady — ladies
In proper names, however, the plural is formed by adding the ending ‑s to the singular: Mary, Marys.
N o t e. — If the final ‑y is preceded by a vowel the plural is formed by simply adding ‑s to the singular.
day — days
key — keys
toy — toys
play — plays
monkey — monkeys
boy — boys
4. If the noun ends in ‑o preceded by a consonant, the plural is generally formed by adding ‑es. Only a few nouns ending in ‑o preceded by a consonant form the plural in ‑s.
cargo — cargoes
potato — potatoes
b u t: piano — pianos
hero — heroes
echo — echoes
solo — solos
photo — photos
All nouns ending in ‑o preceded by a vowel form the plural in ‑s and not in ‑es.
cuckoo — cuckoos
portfolio — portfolios
There are a few nouns ending in ‑o which form the plural both in ‑s and ‑es:
mosquito — mosquitos or mosquitoes
5. With certain nouns the final voiceless consonants are changed into the corresponding voiced consonants when the noun takes the plural form.
(a) The following nouns ending in ‑f (in some cases followed by a mute e) change it into v (both in spelling and pronunciation) in the plural:
wife — wives
calf — calves
sheaf — sheaves
leaf — leaves
thief — thieves
life — lives
shelf — shelves
wolf — wolves
knife — knives
half — halves
There are some nouns ending in ‑f which have two forms in the plural:
scarf — scarfs or scarves
wharf — wharfs or wharves
(b) Nouns ending in ‑th [θ] after long vowels change it into [ð] in pronunciation (which does not affect their spelling).
bath — baths
path — paths
oath — oaths
But [θ] is always retained after consonants (including r) and short vowels:
smith — smiths
myth — myths
health — healths
month — months
birth — births
(c) One noun ending in [s] changes it into [z] (in pronunciation):
house — houses
II. The plural forms of some nouns are survivals of earlier formations.
1. There are seven nouns which form the plural by changing the root vowel:
man — men
woman — women
goose — geese
louse — lice
foot — feet
tooth — teeth
mouse — mice
2. There are two nouns which form the plural in ‑en:
ox — oxen
child — children
N o t e. — The noun brother has, beside its usual plural form brothers, another plural form brethren, which is hardly ever used in colloquial language. It belongs to the elevated style and denotes people of the same creed and not relationship.
The noun cow has, beside its usual plural form cows, a plural kine, which sometimes occurs in poetry.
3. In some nouns the plural form does not differ from the singular: deer, sheep, swine, fish, trout.
III. Some words borrowed from Latin or Greek keep their Latin or Greek plural forms: e. g. phenomenon, phenomena; datum, data; crisis, crises; stimulus, stimuli; formula, formulae; index, indices. Some of these nouns have acquired English plural forms: memorandums, formulas, indexes, terminuses, etc.
The tendency to use the foreign plural is still strong in the technical language of science, but in fiction and colloquial English there is an evident inclination to give to certain words the regular English plural forms in ‑s. Thus in some cases two plural forms are preserved (formulae, formulas; antennae, antennas).
IV. In compound nouns the plural is formed in different ways.
1. As a rule a compound noun forms the plural by adding ‑s to the head-word:
editor-in-chief — editors-in-chief
brother-in-law —
brothers-in-law
looker-on —
lookers-on
2. In some compound nouns the final element takes the plural form:
lady-bird — lady-birds
3. If there is no noun-stem in the compound, ‑s is added to the last element:
forget-me-not — forget-me-nots
merry-go-round — merry-go-rounds
V. Some nouns have only the plural form:
1. Trousers, spectacles, breeches, scissors, tongs, fetters. These are for the most part names of things which imply plurality or consist of two or more parts.
2. Billiards, barracks, works. These nouns may be treated as singulars. We may say: a chemical works, a barracks, etc.
3. Words like phonetics, physics, politics, optics, etc. are usually treated as singulars except in some special cases.
It was not practical politics!
All party politics are top dressing.
4. The word news is treated as a singular.
When she goes to make little purchases, there is no news for her.
The news he gave them was to be read in the lamentations.