Plural Endings: -s or -es?

When students learn how to form the plural of countable English nouns, they realize they have to memorize a lot of irregular plural nouns. At least if the word is regular, they only have to add -s. Or do they? Some English words ending in certain letters take -es instead of -s. Are there any rules we can teach our students to make English plurals a little easier to learn?

Adding -s

Most regular count nouns take the -s ending to form the plural. Students learn this at an early level, and while it’s a fairly straightforward rule, there are some tricky exceptions such as irregular plural forms (but that’s a post for another day).

  • book > books
  • dog > dogs
  • movie > movies

Do we add -s or -es to words ending in the vowel -o? Most of these words follow the normal pattern and take the -s plural ending.

  • radio > radios
  • photo > photos
  • kangaroo > kangaroos

Adding -es

When do we add -es to form the plural? We usually write -es to demonstrate a change in pronunciation. It would be too difficult to pronounce an -s ending after certain similar-sounding consonants (-s, -z, and -x), which is why we need to add an extra syllable. This syllable is written as -es and pronounced as /əz/.

  • kiss > kisses /ˈkɪs əz/
  • quiz > quizzes /ˈkwɪz əz/
  • box > boxes /ˈbɑks əz/

What about a word like “potatoes”? Some words ending in -o must take -es. There aren’t too many of these types of words, but some common ones include:

  • potato > potatoes
  • tomato > tomatoes
  • hero > heroes

Adding -s or -es

What about words that can take either -s or -es? Many words ending in the vowel -o fall into this category, where either plural ending is acceptable and correct. In almost all of these cases, dictionaries list the -es form as the slightly more common form.

  • mango > mangoes/mangos
  • mosquito > mosquitoes/mosquitos
  • zero > zeroes/zeros
  • volcano > volcanoes/volcanos
  • tornado > tornadoes/tornados

For these cases, should we teach our students one rule (i.e., to always add -s or always add -es) or to use the most common dictionary form? This question came up while we were developing our new Famous Things lesson on Volcanoes—we had to decide if we should use volcanos or volcanoes in the lesson.

Both volcanoes and volcanos are acceptable, correct spellings. We chose to use volcanoes since most dictionaries, such as Merriam-Webster and Oxford, list volcanoes as the main entry and volcanos as the variant. Though -s may be the “easier” rule, we felt it was important to teach the most common plural form to students.

Conclusion & Other Rules

There is good news for students! The list of words ending in -o that take only -es is very short, with potatoes being the only common word. This means that if students can’t remember if a word takes -s or -es more often (such as tomatos/tomatoes), they can add only -s and there’s a high chance it will be an acceptable, correct spelling. Remind students, though, that it’s best to use the more common spelling and to look it up when they can.

Some other rules that might be helpful for your students include:

  1. If a word ends in -oe, add -s (e.g., toe > toes, shoe > shoes).
  2. If the letter before the final -o is a vowel, add -s (e.g., patio > patios, video > videos).
  3. If the word ending in -o is short for a longer word (e.g., photograph > photo, automobile > auto), add -s (e.g., photos, autos).


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