#The category of number. Irregular plurals. Singular and plural invariable nouns.
Variable have sg and pl. Invariable have only sg or only pl.
IRREGULAR PLURALS
Voicing: 12 nouns ending in –f form their plurals changing f to ve
Wife, life, wolf, calf, knife, half, self, shelf, thief, leaf, elf, loaf
Mutation or a change of vowel: men, women, mice, lice
-En plural: oxen, children, brethren
Zero: nationality nouns, quantitative nouns (million, dozen), nouns in –s (series, means), animal names (sheep, deer)
SINGULAR INVARIABLE NOUNS
Material nouns: sand, water
Abstract nouns: music, homework
Proper names: London
Substantivized adjectives: the true, the beautiful, the unknown
Some nouns ending in –s: diabetes, billiards,news, aerobics
Some proper names: The United States, Athens
PLURAL INVARIABLE NOUNS
Words denoting things consisting of 2 matching parts: shorts, scissors, jeans
Plural proper names: The Hebrides, the Middle Ages
Unmarked plural nouns: cattle, police, clergy
Substantivized adjectives: the rich, the poor, the old
+outskirts, minutes, thanks, stairs, earnings, finals