Plural of Stimulus

The Quick Answer

The plural of "stimulus" is "stimuli."

The Plural of Stimulus

The plural of "stimulus" is "stimuli."
  • In art, stimuli are things that interests artists and give them new ideas. correct tick
  • Rapid changes, called stimuli, provoke reactions in living organisms that are often very different from those expected from non-living things. correct tick (Professor John Blamire)
The noun "stimulus" has a Latin root, which is the derivation of the plural "stimuli." "Stimuluses" (which adheres to the standard rules for forming plurals) is not an accepted plural.

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The Standard Rules for Forming the Plurals

The table below shows the standard rules for forming the plurals of nouns in English.
Type Example of Type Forming the Plural Plural
Most Nouns lamp
scythe
add s lamps
scythes
Noun Ending s, sh, ch, x or z dress
stimulus
add es dresses
stimuluses
(Just like nucleus (plural "nuclei"), "stimulus" does not form its plural using the standard rules of English.)
Nouns ending [consonant] o hero
zero
tomato
add either s or es
(There are no rules for this - you have to know.)
heroes
zeros
tomatoes
Nouns ending [vowel] o patio
ratio
add s patios
ratios
Nouns ending [consonant] y story
penny
change the y to an i and add es stories
pennies
Nouns ending [vowel] y donkey
chimney
add s donkeys
chimneys
Nouns ending f or fe dwarf
hoof
ves and/or s
(There are no rules - you have to know.)
dwarfs
hooves or hoofs
Exceptions man
louse
some nouns undergo a vowel or letters change men
lice
More exceptions salmon
sheep
some nouns do not change at all salmon
sheep
Foreign rulings stimulus
medium
some nouns adopt foreign rulings stimuli
media
Read more about English spelling rules.

Why Is There Confusion over the Plural of Stimulus?

Confusion arises over the plural of "stimulus" because its plural form ("stimuli") derives from Latin, and native English speakers are unsure whether "stimuluses," which adheres to the standard ruling for forming plurals, has come into use. Many words with Latin roots (e.g., "nucleus," "stadium," "referendum") have either adopted a standard plural ending alongside the Latin one or have dropped the Latin one entirely (e.g., "referendums" correct tick but "referenda" wrong cross).

Unlike these words, "stimuluses" is not an accepted plural. You must use "stimuli."
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This page was written by Craig Shrives.