What Is the Plural of Hypothesis? Simple Grammar Guide

Understanding how words change from singular to plural is one of the most important parts of English grammar. For many words, the rule is simple: add an –s at the end.

However, some words do not follow that pattern. One such word is hypothesis. Because it comes from Greek, it keeps its ancient form when made plural. The correct plural is hypotheses. This guide explains why, how to use it, and clears up common doubts so that you never make a mistake when writing or speaking.

Why is the plural of hypothesis written as hypotheses?

The word hypothesis comes from the Greek roots hypo meaning “under” and thesis meaning “placing” or “proposition.” In classical Greek, the plural was hypotheseis.

When the word entered Latin and then English, it kept the same type of plural form. That is why instead of simply adding s to make hypothesis into hypothesiss, the ending -is changes to -es, giving hypotheses.

Linguists at the University of Oxford and Cambridge have pointed out that English often borrows scientific and scholarly words directly from Greek or Latin without changing their plural endings. Examples include analysis → analyses, crisis → crises, and thesis → theses. Hypothesis belongs to this same group.

READ ALSO: How to Abbreviate Continued: Correct Forms, Uses, and Examples

How do you pronounce hypotheses?

When people first learn the word, they may struggle with its pronunciation, especially in the plural.

• Hypothesis is pronounced hy-POTH-uh-sis (four syllables).

• Hypotheses is pronounced hy-POTH-uh-seez (four syllables as well).

Notice how the final -es in the plural sounds like “eez.” This follows the same pattern as analyses (uh-NAL-uh-seez) or crises (KRY-seez).

What does hypothesis mean?

Before looking at examples, it helps to recall what the word actually means. A hypothesis is a suggested explanation for something, based on limited evidence, that can be tested. In research, science, and even daily life, people often use hypotheses to guide investigation.

According to studies in educational psychology published in 2023, students who practice forming hypotheses while studying science topics show stronger critical thinking skills and better long-term understanding.

In simple terms, a hypothesis is not just a guess but a thoughtful idea that can be tested.

What are some examples of the singular and plural?

Here are clear examples to show the difference:

1. Singular: The scientist proposed a new hypothesis about climate change.
   Plural: Several hypotheses were tested before the team reached a conclusion.

2. Singular: Her hypothesis explained why the machine kept failing.
   Plural: Competing hypotheses offered different reasons for the same problem.

3. Singular: A hypothesis is only useful if it can be proven false through testing.
   Plural: The research project began with five different hypotheses.

4. Singular: Darwin formed a hypothesis about natural selection.
   Plural: Later scientists built on his hypotheses to expand the theory of evolution.

These examples demonstrate the direct switch from hypothesis to hypotheses without any other change in the sentence.

Why is hypothesis considered an irregular plural?

English has both regular plurals and irregular plurals.

• A regular plural simply adds –s or –es (dog → dogs, box → boxes).

• An irregular plural changes form completely or follows older language rules (child → children, mouse → mice, crisis → crises).

Hypothesis is irregular because it changes from -is to -es.

READ ALSO: Past Tense of Seek Explained: Meaning, Usage, and Examples

How can we remember the correct plural?

Students often ask for tricks to remember irregular plurals. Here are a few tested strategies:

1. Look for the ending –is. Words ending in -is often change to -es in the plural. For example:

   • thesis → theses

   • analysis → analyses

   • basis → bases

   • hypothesis → hypotheses

2. Practice with flashcards. Educational research from the University of Michigan in 2022 showed that students who practiced irregular plurals using repetition and flashcards improved recall by more than 40 percent.

3. Use them in sentences. Writing real sentences such as “The teacher asked us to list our hypotheses” helps fix the pattern in memory.

What is the role of hypotheses in science?

The word has deep ties to research and education. A hypothesis is at the heart of the scientific method, which includes observation, forming a hypothesis, testing, and drawing conclusions. Without hypotheses, scientists would lack a clear guide for experiments.

In 2024, a large study published in the journal Science Education showed that high school students trained to generate their own hypotheses before laboratory sessions performed better in tests than those who simply followed given instructions. This proves that learning to form and understand hypotheses has lasting value.

How is hypotheses used in everyday life?

Although people associate the word with science, it is common in daily situations too.

Examples:

1. At work: “Our sales team has two hypotheses about why revenue fell last quarter.”

2. At home: “I have a hypothesis that leaving the window open makes the room cooler.”

3. In law: “The lawyer suggested several hypotheses for what could have happened that night.”

4. In sports: “Coaches often test different hypotheses about training methods before choosing the best plan.”

This shows the plural form is useful beyond textbooks.

Graphical guide: Singular vs Plural of Hypothesis

Here is a simple chart to help you visualize the rule:

Frequently Asked Questions (FAQ)

Is the plural ever written as hypothesis’s or hypothesises?

No. The form hypothesises is incorrect as a plural. However, hypothesises does exist as a verb in British English, meaning “he/she hypothesises.” This often causes confusion. The plural noun is always hypotheses.

Can we say hypotheseses?

No. Adding another es creates a mistake. The word already ends with -es in its correct plural.

Are there other scientific words with similar plurals?

Yes. Words borrowed from Greek often follow the same style:

• crisis → crises

• analysis → analyses

• diagnosis → diagnoses

• hypothesis → hypotheses

Do native speakers often confuse the plural?

Yes, especially when speaking quickly. Many people mistakenly add an extra syllable. Academic writing guides from Harvard and Yale both warn students to pay attention to spelling, as examiners often deduct marks for errors with words like hypotheses.

Is there a difference between multiple hypotheses and a theory?

Yes. A hypothesis is a starting idea that can be tested. A theory is a broad explanation supported by strong evidence after many hypotheses have been tested. For example, Darwin’s hypotheses about natural selection eventually grew into the Theory of Evolution.

What is the adjective form related to hypothesis?

The adjective is hypothetical. For example, “They discussed hypothetical situations based on different hypotheses.”

Can hypotheses be false?

Yes. In fact, a hypothesis must be testable and capable of being proven false. This is what separates scientific reasoning from simple opinion.

Conclusion

The plural of hypothesis is hypotheses. This form comes from the Greek origin of the word, where many scientific and scholarly terms keep their ancient plural endings.

While it may appear irregular, the pattern is consistent with other words ending in -is. By practicing real examples, remembering pronunciation, and understanding the role of hypotheses in both science and daily life, learners can use the word correctly with confidence.

Knowing the correct plural is not only about grammar but also about using precise language in study, work, and conversation. When used well, it shows clarity of thought and respect for the traditions of English and academic writing.