What Is the Plural of Basis?
The plural of basis is bases (pronounced BAY-seez). This is an irregular plural that changes the ending from -is to -es, following the same pattern as crisis → crises and thesis → theses. In business writing, you use basis for one foundation or principle, and bases when referring to two or more foundations, principles, or starting points.
Quick Answer
| Form | Word | Example |
|---|---|---|
| Singular | basis | We made the decision on a basis of trust. |
| Plural | bases | The report examined several bases for the new policy. |
Use basis for one foundation, principle, or reason. Use bases for multiple foundations, principles, or reasons.
Why the Plural Is Confusing
Many learners assume basis follows the regular English rule of adding -es to become basisies or basises. Neither is correct. The word comes from Latin, where nouns ending in -is change to -es in the plural. This same rule applies to analysis → analyses and hypothesis → hypotheses.
Another source of confusion is that bases is also the plural of base (pronounced BAY-siz). So the same spelling can mean two different things depending on context. In business writing, you will almost always mean the plural of basis when you see bases in formal reports or emails.
Formal vs. Informal Use
Formal Business Writing
In formal emails, reports, and presentations, basis and bases are common. You might write:
- “The contract was renewed on a monthly basis.” (singular)
- “We evaluated the proposals on several different bases.” (plural)
Formal contexts prefer precise language. Using bases correctly signals attention to detail.
Informal Conversation
In everyday conversation, people often avoid the plural altogether by rephrasing. Instead of saying “on what bases?”, a native speaker might say “based on what?” or “for what reasons?”. This is natural and avoids the awkwardness of the plural form in casual speech.
Comparison Table: Basis vs. Bases
| Context | Singular (basis) | Plural (bases) |
|---|---|---|
| Decision-making | One reason or principle | Multiple reasons or principles |
| Frequency | On a daily/weekly/monthly basis | On several different bases |
| Logical foundation | The basis of the argument | The bases of the arguments |
| Mathematical or scientific | One basis point | Multiple bases for calculation |
Natural Examples
Here are examples you might actually write or say in a business environment:
- Email context: “Please provide the basis for your cost estimate.” (singular)
- Meeting context: “We need to agree on the bases for our quarterly review.” (plural)
- Report context: “The analysis was conducted on a case-by-case basis.” (singular)
- Strategy context: “The team identified three bases for the new marketing approach.” (plural)
- Conversation: “What’s the basis for that claim?” (singular)
Common Mistakes
Mistake 1: Adding -es incorrectly
Wrong: “We have several basises for the decision.”
Right: “We have several bases for the decision.”
Mistake 2: Using basis as a plural
Wrong: “The report included many basis.”
Right: “The report included many bases.”
Mistake 3: Confusing with base
Wrong: “The bases of the building is strong.” (Here bases is the plural of base, meaning physical foundations.)
Right: “The basis of the argument is strong.” (Singular, meaning logical foundation.)
Better Alternatives and When to Use Them
Sometimes you can avoid the plural bases entirely by using clearer alternatives. This is especially helpful in informal writing or when you want to avoid confusion.
| Instead of | Use | When |
|---|---|---|
| on what bases? | for what reasons? | Casual conversation or email |
| the bases of the decision | the reasons behind the decision | When clarity is more important than formality |
| several bases | several criteria | When referring to standards or measures |
| on a weekly basis | weekly | Shorter, more direct writing |
Use bases when you need to be precise about multiple foundations or principles in formal writing. Use alternatives when the context is informal or when you want to avoid the uncommon plural form.
Mini Practice: 4 Questions
Test your understanding with these sentences. Choose the correct form: basis or bases.
- The company operates on a first-come, first-served ______.
- The researchers presented two different ______ for their conclusions.
- What is the legal ______ for this claim?
- We need to establish clear ______ for performance evaluation.
Answers
- basis (singular, one principle)
- bases (plural, two foundations)
- basis (singular, one reason)
- bases (plural, multiple standards)
FAQ
1. Is “bases” pronounced differently from “base”?
Yes. Bases (plural of basis) is pronounced BAY-seez. Bases (plural of base) is pronounced BAY-siz. The context of your sentence will tell listeners which meaning you intend.
2. Can I use “basis” in plural form in everyday speech?
You can, but it sounds formal. Most native speakers rephrase to avoid the plural. For example, instead of “on what bases?”, they say “based on what?” or “for what reasons?”. In writing, especially business writing, using bases is perfectly correct and expected.
3. What is the difference between “basis” and “base”?
Basis is abstract and refers to a principle, reason, or foundation for an idea or decision. Base is more concrete and refers to a physical foundation, a location, or a starting point. For example, “the basis of the theory” vs. “the base of the building”.
4. Are there other words that follow the same pattern as basis?
Yes. Many English words ending in -is change to -es in the plural. Common examples include crisis → crises, thesis → theses, analysis → analyses, and hypothesis → hypotheses. Learning this pattern will help you with all of them.
Final Tip for Business Writing
When you write a business email or report, decide whether you need one foundation or many. If it is one, use basis. If it is more than one, use bases. If you are unsure, try replacing the word with “reason” or “reasons”. If “reasons” fits, then bases is correct. If “reason” fits, use basis. This simple test will keep your writing accurate and professional.
For more help with similar plural forms, visit our Common Plural Forms section. If you have questions about other confusing word pairs, check our Confusing Plurals guide. For general questions about singular and plural usage, see our Singular or Plural Checks page. You can also learn about the rules behind these patterns in our Plural Spelling Rules category. For any other inquiries, please visit our FAQ page.
