What’s the Plural of Basis? Is it Baseis or Bases?

Language learners often stumble when they come across the word basis. It looks simple at first, but when you need its plural, confusion sets in. Should it be baseis? Or perhaps bases? This uncertainty is understandable because English borrows words from Greek and Latin, and many of them don’t follow the regular “just add -s” rule.

In this guide, you’ll learn the correct plural of basis, why it takes that form, how to use it properly in sentences, and what common mistakes to avoid. We’ll also break down related grammar rules, provide a reference table, and answer the most frequently asked questions. By the end, you’ll not only know the plural of basis—you’ll feel confident using it.

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The Correct Plural of Basis

Let’s start with the answer up front: the plural of basis is bases.

• Singular: basis
  
• Plural: bases
  

Here’s how it looks in real sentences:

• The basis of her decision was personal experience.
  
• The company built its strategy on multiple bases.
  

Notice something important here. The plural form is not baseis, even though many people mistakenly assume that’s correct. English simply doesn’t recognize baseis as a word. If you type it into most word processors, you’ll see it underlined in red because it’s not standard usage.

Key takeaway: If you need the plural of basis, always write bases.

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Why Is the Plural “Bases” and Not “Baseis”?

The confusion comes from the word’s Greek origin. Basis entered English from the Greek word βάσις (basis), meaning “a step” or “foundation.” When Greek words ending in -is are pluralized, they usually shift to -es. English carried this pattern forward.

Here’s how it works with other Greek-derived words:

• thesis → theses
  
• analysis → analyses
  
• crisis → crises
  
• diagnosis → diagnoses
  

So, basis naturally follows the same rule:

• basis → bases
  

This isn’t just a spelling choice—it reflects the historical structure of English vocabulary. Many of these borrowed forms retain their original pluralization patterns, which is why baseis looks wrong to trained eyes.

Linguists often call this a classical plural—a form inherited directly from classical languages rather than being adjusted to regular English patterns.

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How to Use Basis vs. Bases in Sentences

Understanding the correct plural is one thing. Using it naturally is another. Let’s compare examples:

• Singular (basis):
  
  • The basis of the agreement was mutual trust.
    
  • Every scientific theory must rest on a solid basis.
    
• Plural (bases):
  
  • Philosophy and science have different bases of reasoning.
    
  • Their campaign drew support from various social bases.
    

The difference lies not just in number but sometimes in meaning. While basis points to a single foundation, bases often indicates different kinds of foundations or principles.

For example:

• The basis of democracy is equality.
  
• Democracies can rest on different bases, such as cultural traditions, legal systems, or civic values.
  

Notice how pluralizing the word changes the nuance—it suggests multiple starting points or types of support.

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Common Mistakes and Misconceptions

Because the word feels tricky, learners often stumble in predictable ways. Let’s clear those up.

Mistake 1: Writing baseis

Many people think baseis looks more “logical,” but it’s simply not correct in English. If you use it, readers may think you’re inventing a word.

Mistake 2: Confusing bases (plural of basis) with bases (plural of base)

Here’s where it gets tricky. The word bases also happens to be the plural of base. And base has many meanings: foundation, chemical substance, or even a military base.

To avoid confusion, check context carefully.

• As the plural of basis:
  
  • The conclusions rest on solid bases.
    
• As the plural of base:
  
  • The army built several military bases near the border.
    
  • In chemistry, strong bases neutralize acids.
    

Mistake 3: Forgetting Pronunciation Differences

Even though they’re spelled the same, the plural of basis and the plural of base don’t always sound alike.

• Basis → bases (pronounced BAY-seez)
  
• Base → bases (pronounced BAY-siz or BAY-ses)
  

This subtle difference often escapes non-native speakers. But in spoken English, context usually clears it up.

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Quick Grammar Rules for Words Ending in -is

One of the best ways to remember how basis works is to see how other words ending in -is behave.

Here’s a reference table:

Singular	Plural	Example Sentence
basis	bases	The conclusions rest on several bases.
thesis	theses	Students defended their theses confidently.
crisis	crises	The world faced multiple crises in the 20th century.
analysis	analyses	The researcher presented detailed analyses.
hypothesis	hypotheses	Scientists tested several hypotheses.
diagnosis	diagnoses	The doctor made accurate diagnoses.

The Rule

• Words ending in -is often replace it with -es in plural form.
  

Exceptions

Not every -is word behaves this way. Some words adapted differently as English evolved. For instance:

• iris → irises (though irides also exists in technical usage)
  
• campus → campuses (because it’s Latin, not Greek)
  

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Real-World Examples of Basis and Bases

Sometimes, it helps to see how respected sources use these words.

Academic Example

“The basis of the theory lies in observable data.”
— Journal of Modern Science

Political Example

“Elections provide different bases of legitimacy in democratic societies.”
— The Economist

Everyday Example

• Trust is the basis of friendship.
  
• Strong relationships often have multiple bases, including respect, honesty, and empathy.
  

These examples show how the word works across different registers—academic, professional, and casual.

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Case Study: A Common Error in Academic Writing

A university study once examined the most frequent errors among international students learning English. One of the findings was that words with Greek plurals—such as analysis, thesis, and basis—caused repeated problems.

What Students Did

• Wrote baseis instead of bases.
  
• Confused basis with base.
  
• Used basis in plural contexts without changing the form.
  

Why It Happened

• Overgeneralizing rules (thinking every plural just takes “-s”).
  
• Misunderstanding how borrowed words behave in English.
  
• Lack of exposure to academic writing where these words appear frequently.
  

The Fix

Teachers recommended creating a personal reference chart of tricky plurals. Over time, repeated use reinforced the correct forms.

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FAQs About Basis and Bases

What is the plural of basis in American and British English?

It’s bases in both American and British English. The spelling doesn’t change across dialects.

Is “baseis” ever used in any language?

While it resembles a Greek-looking plural, baseis is not correct in English. Ancient Greek had its own plural forms, but modern English standardized on bases.

Are bases (plural of basis) and bases (plural of base) pronounced the same?

Not always. The plural of basis is pronounced BAY-seez, while the plural of base can be BAY-siz or BAY-ses.

Why do so many Greek words follow irregular plural patterns?

Because English borrowed them directly from classical Greek and Latin. Instead of forcing them into regular pluralization, English preserved their original endings.

Can I simply add “-s” to basis?

No. Writing basiss or basises is incorrect. The correct plural is always bases.

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Conclusion

The question, What’s the plural of basis? trips up many English learners. The answer is straightforward: the plural of basis is bases. Not baseis, not basises—just bases.

Remember these key points:

• Basis → bases is the correct form.
  
• This follows a Greek-derived rule where -is changes to -es.
  
• Don’t confuse bases (plural of basis) with bases (plural of base)—context matters.
  
• Pronunciation differs slightly: BAY-seez vs. BAY-siz.
  
• Words like thesis, analysis, and crisis follow the same rule.
  

Mastering irregular plurals might feel challenging at first, but with practice and exposure, you’ll find them becoming second nature. The next time you need to write about foundations, principles, or starting points, you’ll know exactly which plural to use.