Whats the Plural of Basis: Understanding Grammatical Number

Basis Becomes Bases — See the Pattern

Look at these words. Can you see what happens at the end?

• one basis → two bases
• one crisis → two crises
• one analysis → two analyses
• one thesis → two theses

Did you see the pattern? The -is at the end changes to -es. This rule works for many English words that come from Greek.

Why It Is Bases and Not Basises

Most English plurals just add -s or -es to the end of the word: cat → cats, box → boxes. But the word basis comes from Greek. Greek words that end in -is follow a special rule. The -is changes to -es:

• basis → bases (not “basises”)
• crisis → crises (not “crisises”)
• thesis → theses (not “thesises”)

A basis is the main idea or starting point that something is built on. Your plan, your argument, your friendship — they all need a basis. You say it like “BAY-sis” for one, and “BAY-seez” for more than one. The sound changes a lot, even though the spelling change looks small.

Easy way to remember: Think of crisis → crises. Most people know that one. The word basis works the same way: basis → bases.

How to Use Basis and Bases in Everyday English

• Trust is the basis of every good friendship. (one main idea)
• The teacher gave us homework on a weekly basis. (one regular pattern)
• Her two main bases for the plan were time and money. (more than one)
• The company has offices on a part-time basis in three cities. (one type of arrangement)
• The doctor’s report listed several bases for the new diet. (more than one reason)

You are doing great. Now let us look at the mistakes most learners make with this word.

The Most Common Mistakes With Basis

Many learners write “basises” because most English plurals just add -s or -es. That is a smart guess — but it does not work for words from Greek. Even native speakers’ children make this mistake when they are learning to talk. So if you get confused, you are not alone.

How to remember: The word ends in -is. If you see -is at the end, change it to -es. Basis → bases. Simple.

One small thing to watch out for: the word base (without -is) is a different word. A base is the bottom part of something, like the base of a lamp or a baseball base. Its plural is also bases — same spelling, but a different sound: “BAY-siz” instead of “BAY-seez”. Don’t worry — the sentence around it will always make the meaning clear.

Other words like this: crisis → crises, analysis → analyses, thesis → theses, oasis → oases, hypothesis → hypotheses.

Test Yourself: Basis or Bases?

Choose the correct answer for each sentence. Click Check to see if you are right.

Keep Going — You Are Building Something

You just learned that basis becomes bases. That is one more plural you will never get wrong again.

But here is something interesting. The word oasis follows the same Greek rule — but most learners get the sound wrong. Do you say “OH-uh-sees” or “oh-AY-seez” when you talk about more than one? And what is an oasis, anyway, in everyday English — not just in the desert?

Next lesson: What Is the Plural of Oasis?

Sources

1. Definition of basis.
2. Synonyms for basis.
3. Origin of basis.

Khamis Maiouf

My name is Khamis Maiouf. I am the creator of the English Teacher Site, dedicated to providing valuable resources and insights for students around the world. With a passion for education and a commitment to helping students enhance their skills, I aim to make English teaching more effective and enjoyable for both educators and students.