The Grammar Doctor

Plurals

Regular Plurals

Most nouns form the plural by adding -s or -es to the singular form.
catcats
househouses
pencilpencils

Plurals of Compound Words

To form the plural of a compound word, add -s or -es to the key word.
mother-in-law  mothers-in-law
runner-up runners-up
letter of credit letters of credit
mousetrap mousetraps

Words ending in -s, -x, -ch, -sh, or z

Add -es to words ending with any of these letters.
waltz waltzes
watch watches
wish wishes
summons summonses

Words ending in -y

To form the plural of words ending in -y preceded by a consonant, change the -y to -i and add -es
family families
copy copies
To form the plural of words ending in -y preceded by a vowel, add -s.
boy boys
monkey monkeys

Words ending in -o

Words ending in -o preceded by a vowel form the plural by adding -s.
ratio ratios
shampoo shampoos
Words ending in -o preceded by a consonant sometimes add -s to for the plural and sometimes add -es. If you're not sure, you can look in the dictionary.
typo typos
potato potatoes
motto mottoes or mottos

Words ending in -f, -fe, or -ff

Some words with these endings form the plural by adding -s. Others change the -f or -fe to -ve and then add -s. If you're not sure, you can check in the dictionary.
belief beliefs
leaf leaves
knife knives

Irregular Plurals

woman women
child children
mouse mice (This goes for computer mice as well as little rodents.)
foot feet

Foreign Plurals

Words borrowed from other languages sometimes keep their original plural form. Sometimes they follow the English pattern to form plurals. Some foreign words in English form plurals both ways.
singular English plural foreign plural
focus focuses foci
nucleus nucleuses nuclei
census censuses
bacterium bacteria
stratum strata
crisis crises
Back to nouns