Plural of Thesis

The Quick Answer

The plural of "thesis" is "theses."

The Plural of Thesis

The plural of "thesis" is "theses."
  • PhD theses are usually over two hundred pages. correct tick
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The noun "thesis" has a Greek root, which is the derivation of the plural "theses." There is no alternative English plural form. The noun "thesis" adheres to the standard rules for forming the plurals of nouns in English (shown in the table below).

Table of Contents

  • Are You Good at Plurals?
  • The Standard Rules for Forming the Plurals
  • Why Is There Confusion over the Plural of Thesis?
  • Ready for the Test?
plural of thesis

Are You Good at Plurals?

Here's a quick test.
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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 box
dress
add es boxes
dresses
Nouns ending [consonant] o zero
tomato
add either s or es
(There are no rules for this - you have to know.)
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
Nouns ending is thesis
crisis
change the "is" to "es" theses
crises
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 fungus
medium
some nouns adopt foreign rulings fungi
media
Read more about English spelling rules.

Why Is There Confusion over the Plural of Thesis?

"Theses" is the only way to make the noun "thesis" plural.

Confusion arises because some mistakenly believe that all nouns ending in "s" should form a plural that adds "es" to the end of the word. When a noun ends with "is," you need to replace the "is" with an "es" to form the plural. This is because its plural form derives from Greek.
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This page was written by Craig Shrives.