Plurals signify that there is more than one of something. Most words in the English language are made plural by simply adding -es to the end of the word. For example, boy becomes boys, kitten becomes kittens, and so on.

So far, so good. The problem comes for words that do not form their plurals in this simple manner. Here are some rules that can help you correctly form plurals for some of these words.

1. To form the plural of a word that ends with a consonant followed by -y, change the -y to i, and add -es.
   
   city - cities     lady - ladies     candy - candies
   
   However, to form the plural of a word that ends with a vowel followed by -y, simply add -s.
   
   turkey - turkeys     donkey - donkeys     valley - valleys
2. To form the plural of most words that end with -f or -fe, simply add -s.
   
   chief - chiefs     safe - safes     gulf - gulfs
   
   However, in some cases, the plural is formed by changing the -f to v, and adding -es.
   
   wife - wives     leaf - leaves     knife - knives
3. For most words that end with -o preceded by a consonant, the plural is formed by adding -es.
   
   potato - potatoes     hero - heroes     echo - echoes
   
   When -o is preceded by a vowel, the plural is formed by simply adding -s.
   
   video - videos     patio - patios     studio - studios
4. For compound words that are not hyphenated or separated by spaces, the plural is formed by adding -s or -es.
   
   checkbook - checkbooks     sandbox - sandboxes     windmill - windmills
   
   However, when a compound word is hyphenated or separated by spaces, -s or -es is added to the word that is to be pluralized. The word to be pluralized is the main word in the compound word.
   
   mother-in-law - mothers-in-law     poet laureate - poets laureate
   
   If you can’t identify a main word to be made plural, simply add -s or -es.
   
   grown-up - grown-ups     lieutenant-colonel - lieutenant-colonels

These rules will not help you with words that have irregular plural forms such as mice and stimuli. But they will help you correctly form the plural for many of the words you encounter.