Why is the plural of “thesis” not “thesises”?

The plural of thesis is not thesises because thesis is an irregular plural noun and doesn’t follow the regular pluralization rules, which add “-s” or “-es” to the end of the singular to form the plural.

Thesis is a Greek-derived irregular plural that follows Greek pluralization rules, which change the “-is” at the end of the singular form to “-es” in the plural. So, the plural of thesis is theses.

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Plural of Thesis | Definition & Examples

Frequently asked questions: Plurals

Is “sullabus” a word?: “Sullabus” is not a word. It’s a common misspelling of the word “syllabus.”

When you see “sullabus” written somewhere, it’s most likely a typo because the U and Y keys are right next to each other on a keyboard.

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Is it “mices” or “mice”?: Mice is the correct plural of mouse whether you’re talking about a computer accessory or a hairy rodent. Mices is not a word and is incorrect in every context.

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What is the plural of computer mouse?: Both mice and mouses are acceptable plural forms of mouse in the context of the computer accessory (e.g., “The computer store got a shipment of mice/mouses today”).

Mice is an irregular plural noun that uses irregular pluralization rules, while mouses uses the regular pluralization rules of adding “-s” or “-es” to the end of the singular form. After the invention of the computer mouse in the 1960s, it was decided that mouses is also an acceptable plural form along with the typical plural mice.

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Is “mouses” or “mices” correct?: Mouses is only correct as a plural of mouse in the context of computer accessories. Mouses is incorrect in the context of hairy rodents regardless of the number of mice.

Mices is not a word and is incorrect in every context.

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Is “thesis” plural?: Thesis is singular, and the plural of thesis is theses.

Thesis is an irregular plural noun that doesn’t follow the regular pluralization rules of adding “-s” or “-es” to the singular to form the plural.

Use Scribbr’s free Grammar Checker to ensure you use the correct noun forms in your online documents.
Is “sheep” plural?: Sheep is both singular and plural. Sheep is an irregular plural noun called a zero plural, which is where the word remains the same whether it’s the singular or plural form.

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What is a zero plural?: A zero plural is a type of irregular plural noun that stays the same whether you refer to the singular or plural (e.g., sheep/sheep and aircraft/aircraft).

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What does “biases” mean?: Biases are preconceived notions or opinions that influence how one thinks and acts, often in a subjective way. They tend to come from unconscious assumptions from past personal experiences and cultural norms and can influence our thoughts and behaviors in a variety of contexts.

Biases is the plural form of bias. There are many different types of bias that are important to identify in research settings, and biases are also frequently evident in everyday life.

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What is the pronunciation of “biases”?: The pronunciation of biases is [bahy-uh-siz]. Biases is the plural of bias and is a regular plural noun, formed by adding “-es” to the base word. Its ending is pronounced like other regular plural nouns (e.g., “dresses,” “foxes”), not like the irregular plurals theses or diagnoses.

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Is “dices” a word?: Dices is a word, but it’s neither the correct plural of dice nor die. Dices is the third-person singular form of the verb “to dice,” which means to cut something into small cubes, most often in the context of cooking.

Dice is the correct plural form of the singular word die.

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Is “dice” plural or singular?: Dice is the plural form of the word die, which is singular. Some people wonder what the plural of dice is without realizing that “dice” is, in fact, already the plural of “die,” which is singular.

“Dice” is an irregular plural noun that doesn’t follow regular pluralization rules of simply adding “-s” or “-es” to the end of the singular form, which is why “dies” and “dices” are incorrect.

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How do you spell “syllabus”?: The correct spelling is S-Y-L-L-A-B-U-S. Be careful not to confuse it with common misspellings like “syllabys” or “syllubus.”

The plural of syllabus is “syllabi” or “syllabuses.”

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Why is the plural of “diagnosis” not “diagnosises”?: The plural of diagnosis is diagnoses, not diagnosises. Diagnoses is considered an irregular plural, which doesn’t follow the pluralization rules of regular plural nouns.

Diagnosis is a Greek-derived word, meaning it follows the Greek rules of pluralization, so the “-is” is changed to “-es.”

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What does “syllabys” mean?: “Syllabys” is a common misspelling of the noun “syllabus.” The correct spelling is S-Y-L-L-A-B-U-S.

It is commonly typed like this because it’s either a misspelling (because of a mispronunciation of the word) or a typo (because the U and Y keys are right next to each other).

Scribbr’s free Grammar Checker will notice and correct typos like this in all of your online documents.
What is a synonym for “hypothesis”?: Some synonyms for the word “hypothesis” include:

Premise

Presumption

Assumption

Supposition

Theory

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Is “hypothesis” a word?: Yes, hypothesis is a word. It refers to an assumption or explanation based on limited evidence and is the starting point for further experimentation.

The plural of hypothesis is hypotheses.

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What is a synonym for cactus?: The word cactus isn’t listed in the thesaurus, as it refers to a very specific type of plant.

However, some possible synonyms that refer to very similar types of plants are succulent, prickly pear, and yucca.

Scribbr’s free Paraphrasing Tool can help you easily find the right synonyms for the words in your writing.
How do you spell cactus?: The word cactus is spelled C-A-C-T-U-S.

Cactus has two correct plural forms; one plural of cactus is spelled C-A-C-T-I, and the other plural version is spelled C-A-C-T-U-S-E-S.

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What is the x and y axis on a graph?: On a graph, the vertical axis is called the y-axis, and the horizontal axis is called the x-axis.

The x– and y–axes intersect with each other to form a coordinate plane (also called a Cartesian plane). The Cartesian plane is used to plot points, lines, and curves in algebra, geometry, and calculus.

Each point on the coordinate plane is represented by an ordered pair of numbers displayed as (x,y), where x is the horizontal position (measured along the x-axis), and y is the vertical position (measured along the y-axis).

Scribbr’s free Grammar Checker will ensure you’re using the correct form of the word axis.
Is axis singular or plural?: The word axis is singular; the plural form is axes.

Axes is a Latin-derived irregular plural noun and doesn’t follow the pluralization rules of regular plural nouns. Instead of adding “-s” or “-es” to the end of the word like regular plural nouns, you change the “-is” at the end of the word to “-es” to form the plural.

You can use Scribbr’s free Grammar Checker to ensure you’re using the correct plural of axis.
Is it axises or axis?: The plural of axis is axes, not “axises.”

The word axes is considered an irregular plural noun and is derived from Latin origins. This means it follows the Latin rules of pluralization, not the regular pluralization rules of adding “-s” or “-es.”

Latin-derived words that end in “-is” are made plural by changing the “-is” to “-es.”

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Is “analysis” singular or plural?: The word analysis is a singular noun. The plural of analysis is analyses.

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Why is “analysises” not the plural of “analysis”?: The plural of analysis is analyses because it’s an irregular plural that doesn’t follow the pluralization rules of regular plural nouns. It’s grammatically incorrect to simply add an “-s” or “-es” to “analysis” and call it “analysises.”

“Analysis” is an irregular plural that follows the Greek pluralization rules, meaning you must change the “-is” at the end of the singular form to “-es” to form the plural.

Scribbr’s free Grammar Checker can help you make sure you’re using the correct plural forms of words.
Is diagnosis plural?: Diagnosis is the singular form. The plural of diagnosis is diagnoses.

Diagnosis is not a zero plural noun, which is a word that remains the same in both the singular and plural forms. Diagnosis is a Greek-derived word that changes the “-is” in the singular to “-es” in the plural.

Scribbr’s Grammar Checker can help you fix errors with plural forms in your writing.

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Why is the plural of “thesis” not “thesises”?

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