Rules for Irregular Plural Formation of Nouns

Variations of the final -s rule

• Nouns that end with -s, -z, -x, -sh, -ch 

Add -es

glass/glasses, buzz/buzzes, box/boxes, bush/bushes, switch/switches
 

• Nouns that end in -o 

  
  Add -es

  potato/potatoes, echo/echoes, hero/heroes

  exceptions: studio/studios, piano/pianos, kangaroo/kangaroos, zoo/zoos

  either: buffalo/buffalo(e)s, cargo/cargo(e)s, motto/motto(e)s, 

  volcano/volcano(e)s
  
  

• Nouns that end in a consonant + -y 

  
  Change -y to -i and add -es

  baby/babies, spy/spies, poppy/poppies
  
  

• Nouns that end in -f, or -fe 

  
  Change the -f to -v and add -es
  
  

  shelf/shelves, wolf/wolves, knife/knives, wife/wives

Nouns adopted from other languages

• Singular ends in -is 

  
  Plural ends in -es

  analysis/analyses, basis/bases
  
  

• Singular ends in -um 

  
  Plural ends in -a

  datum/data, curriculum/curricula
  
  

• Singular ends in -on 

  
  Plural ends in -a

  criterion/criteria, phenomenon/phenomena
  
  

• Singular ends in -a 

  
  Plural ends in -ae

  formula/formulae, antenna/antennae
  
  

• Singular ends in -ex or -ix 

  
  Plural ends in -ices

  appendix/appendices, index/indices
  
  

• Singular ends in -us 

  
  Plural ends in -i

  focus/foci, stimulus/stimuli
  
  

• Singular ends in -us 

  
  Plural ends in -a

  corpus/corpora, genus/genera
  
  

• Singular ends in -eau 

  
  Plural ends in -eaux

  bureau/bureaux, beau/beaux

Nouns that have only a plural form and so take a plural verb

• Things that come in pairs 

  
  Tools: glasses, scissors, binoculars, forceps, tongs, tweezers

  Clothes: jeans, pants, pajamas, shorts, trousers
  
  

• Nouns that end in -s but have no singular _aggregate nouns

  
  accommodations, amends, archives, arms (weapons), bowels, intestines 

  brains (intellect), clothes, communications, congratulations, contents 

  stairs, thanks, goods
  
  

• Nouns that are plural but do not end in -s 

  
  people, police, cattle, people