What Is the Plural Hypothesis? Meaning, Rules, and Examples

The correct plural hypothesis is hypotheses.

Use hypothesis when you mean one proposed explanation. Use hypotheses when you’re discussing two or more proposed explanations, predictions, or ideas.

Singular: The researcher developed one hypothesis.
Plural: The researchers tested several hypotheses.

The spelling changes from -sis to -ses, and the pronunciation changes, too. This pattern also appears in words such as analysis, crisis, and thesis.

Highlights

Understanding the Singular and Plural Forms

Hypothesis is a singular noun. It refers to one idea that can be examined through research, observation, or testing.

Hypotheses is the plural form. It describes more than one possible explanation or testable prediction.

Number	Word	Example
Singular	hypothesis	Her hypothesis explains the unusual results.
Plural	hypotheses	The team compared three competing hypotheses.

You shouldn’t write hypothesises, hypothesiss, or hypothesis when referring to multiple ideas. The correct plural spelling is always hypotheses.

What Does “Hypothesis” Mean?

A hypothesis is a proposed explanation for an observation or research question. It isn’t simply a random guess. A useful hypothesis gives you something specific to investigate.

For example, a student might notice that plants near a window grow faster. The student could form this hypothesis:

Plants grow faster when they receive more sunlight.

The student can then design an experiment, collect supporting evidence, and compare the results with the prediction. A hypothesis may be supported by evidence, or the results may show that it needs revision.

In the scientific method, a hypothesis often connects an observation with a testable prediction.

Why Does “Hypothesis” Become “Hypotheses”?

Most English nouns form plurals by adding -s or -es. However, some words borrowed from Greek follow a different pattern.

For nouns ending in -sis, the plural commonly changes that ending to -ses:

hypothesis → hypotheses
analysis → analyses
diagnosis → diagnoses
crisis → crises
thesis → theses

This is why hypothesiss is incorrect. The word doesn’t take a regular ending. Instead, its final syllable changes in both spelling and pronunciation.

Common Nouns Ending in “-Sis”

Learning related words can make the plural hypothesis form easier to remember. Several familiar nouns use the same Greek-based pattern.

Singular	Plural
analysis	analyses
basis	bases
crisis	crises
diagnosis	diagnoses
thesis	theses
synthesis	syntheses
synopsis	synopses
hypothesis	hypotheses

Be careful with pronunciation. For instance, hypothesis sounds roughly like hy-PAH-thuh-sis, while hypotheses sounds roughly like hy-PAH-thuh-seez.

Hypothesis vs. Theory: What’s the Difference?

A hypothesis is a specific, testable explanation. A theory is a broader explanation supported by substantial evidence from repeated research.

For example, a scientist might propose a hypothesis about how temperature affects plant growth. After many studies support related findings, researchers may discuss those findings within a larger scientific theory.

In everyday conversation, people sometimes use theory to mean a personal guess. In science, however, a theory has strong evidential support. A hypothesis remains an idea that researchers still need to test.

Synonyms for Hypothesis

The best synonym depends on the context. In academic writing, some alternatives sound more precise than others.

Possible synonyms include:

assumption
supposition
proposition
conjecture
proposed explanation
prediction
idea
interpretation
tentative conclusion

These words aren’t always interchangeable. For example, prediction usually describes an expected result, while hypothesis describes an explanation that can lead to a prediction.

The Origin of the Word “Hypothesis”

The word hypothesis entered English through French and Late Latin, with roots in the Greek word hypothesis. Its original sense related to a foundation, proposal, or underlying idea.

That history also explains why the word has an irregular plural. English has borrowed many Greek nouns while retaining parts of their original spelling patterns.

You’ll see the same influence in words such as analysis, diagnosis, thesis, and synthesis. Their plural forms don’t simply add -s.

How to Use “Hypothesis” and “Hypotheses” in a Sentence

Use hypothesis for one proposed explanation:

The researcher tested a hypothesis about sleep and memory.
Her hypothesis predicted that warmer water would speed up the reaction.
The experiment didn’t support his original hypothesis.

Use hypotheses for two or more proposed explanations:

The researchers compared several hypotheses.
Three hypotheses could explain the unexpected result.
The study evaluated competing hypotheses about consumer behavior.

A quick test can help: if you can replace the word with one explanation, choose hypothesis. If you mean multiple explanations, choose hypotheses.

Common Mistakes With the Plural of Hypothesis

The most frequent mistake is adding a regular plural ending. Writers may use hypothesiss or simply leave the word as hypothesis.

These forms are incorrect:

three hypothesiss
several hypothesis
different hypothesises

Use hypotheses instead:

three hypotheses
several hypotheses
different hypotheses

Another common error involves subject-verb agreement. Because hypotheses is plural, it usually takes a plural verb:

Correct: The hypotheses are still being tested.
Incorrect: The hypotheses is still being tested.

The singular form takes a singular verb:

Correct: The hypothesis is testable.

Why the Correct Form Matters in Academic Writing

Using the correct plural shows that you understand both the word’s meaning and its grammar. This matters in research papers, lab reports, essays, and professional writing.

For example:

The study examined two hypotheses concerning customer retention.

That sentence clearly tells readers that the researchers considered two separate explanations. Using two hypothesis would make the sentence grammatically incorrect and less polished.

When writing about research, also make sure each hypothesis describes something that can be evaluated with evidence. A vague statement may sound thoughtful but remain difficult to test.

Quick Practice: Choose the Correct Form

Choose hypothesis or hypotheses in each sentence:

The scientist proposed one ______ about the chemical reaction.
The research team tested four competing ______.
Her ______ was supported by the experimental results.
Several ______ were rejected after the second trial.
The article presents a new ______ about language development.

Answers

hypothesis
hypotheses
hypothesis
hypotheses
hypothesis

A simple memory tip helps: one hypothesis, two hypotheses.

Frequently Asked Questions

What Is the Plural of Hypothesis?

The plural of hypothesis is hypotheses. Use it when referring to two or more proposed explanations or testable predictions.

How Do You Spell the Plural of Hypothesis?

Spell the plural hypotheses. The ending changes from -sis to -ses, not -siss or -seses.

Is “Hypothesis” Singular or Plural?

Hypothesis is singular. It refers to one idea, while hypotheses refers to multiple ideas, explanations, or predictions.

Why Is “Hypothesis” an Irregular Plural?

It has an irregular plural because the word comes from Greek. Greek-derived nouns ending in -sis often change to -ses.

What Is a Common Mistake With Hypothesis?

A common mistake is writing hypothesiss or using hypothesis for several ideas. The correct plural is hypotheses.

When Should You Use “Hypotheses” Instead of “Hypothesis”?

Use hypotheses when your sentence refers to two or more proposed explanations, predictions, or research ideas.

What Is the Difference Between a Hypothesis and a Theory?

A hypothesis is a specific testable explanation. A theory is a broader explanation supported by extensive evidence and repeated research.

Can “Hypotheses” Refer to Two or More Ideas?

Yes. Hypotheses can describe two or more related or competing explanations in a research study.

Is “Hypotheses” Pronounced Differently From “Hypothesis”?

Yes. Hypothesis ends with a “sis” sound, while hypotheses ends with a “seez” sound.

Does “Hypotheses” Take a Singular or Plural Verb?

Hypotheses takes a plural verb. For example, “The hypotheses are being tested.”

What Is the Plural of a Null Hypothesis?

The plural is null hypotheses. For example, “The researchers compared two null hypotheses.”

Is “Hypotheses” Used Outside Scientific Writing?

Yes. You can use hypotheses in history, business, education, psychology, and everyday discussions involving testable ideas.

Final Thoughts

The Plural Hypothesis form is hypotheses. That answers the common question, “what is the plural of hypothesis?” Use hypothesis for one proposed explanation and hypotheses for two or more. Although the spelling changes, the rule becomes easier once you recognize the pattern.

If you’re searching for the plural of hypothesis, remember that the correct hypothesis plural changes -sis to -ses. The same pattern appears in words such as analysis, crisis, and thesis. Therefore, hypotheses is the correct plural for hypothesis, while hypothesiss and hypothesises are incorrect.

A clear example can help: “The scientist tested one hypothesis” refers to one idea. “The scientists compared several hypotheses” refers to multiple ideas. Keep that distinction in mind whenever you write research papers, lab reports, or academic explanations. With a little practice, choosing between hypothesis and hypotheses will feel natural.

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