Common Mistakes with the Plural of Index
If you write about data, finance, or research, you have likely needed the plural of index. The short answer is that both indexes and indices are correct, but they are used in different contexts. Indexes is the standard plural for everyday use, especially in computing and general writing. Indices is the traditional Latin plural, preferred in academic, financial, and technical fields. Choosing the wrong one can make your writing sound either too informal or overly stiff.
Quick Answer: Which Plural Should You Use?
- Indexes: Use for general writing, business emails, and computing (e.g., database indexes).
- Indices: Use for formal academic papers, financial reports (e.g., stock market indices), and scientific research.
- Both are grammatically correct. Your choice depends on your audience and tone.
Understanding the Two Plurals
English borrowed index from Latin, where its plural was indices. Over time, English speakers began applying the regular -es ending, creating indexes. Today, both forms are accepted, but they have settled into different professional niches.
When to Use Indexes
Indexes is the more common plural in everyday English. It sounds natural in conversation, internal company memos, and most business writing. If you are writing a quick email to a colleague about a spreadsheet, indexes is your best choice.
Formal vs. Informal Tone: Indexes is neutral. It works in both formal and informal contexts, though it leans slightly toward the informal side. In a formal business report, you can still use indexes without sounding uneducated.
Email Context: In a casual email, indexes feels natural. For example: “Please update the indexes in the shared folder.”
Conversation Context: In spoken English, indexes is almost always used. Saying indices in conversation can sound pretentious unless you are in a very technical discussion.
When to Use Indices
Indices is the preferred form in academic writing, finance, and scientific research. If you are writing a paper for a journal, a financial analysis, or a technical document for a specialized audience, indices signals that you know the field’s conventions.
Formal vs. Informal Tone: Indices is distinctly formal. Using it in a casual conversation or a friendly email can feel out of place.
Email Context: In a formal email to a client or a professor, indices is appropriate. For example: “The market indices showed a significant drop this quarter.”
Conversation Context: In a meeting with financial analysts, indices is expected. In a general team meeting, indexes is safer.
Comparison Table: Indexes vs. Indices
| Feature | Indexes | Indices |
|---|---|---|
| Origin | English regular plural | Latin plural |
| Common Usage | General writing, computing, everyday business | Academic, financial, scientific |
| Tone | Neutral to informal | Formal |
| Email Example | “Please check the database indexes.” | “The economic indices are published quarterly.” |
| Conversation Example | “I updated the indexes in the report.” | “The indices we track have changed.” |
| Audience | General readers, colleagues | Specialists, academics, analysts |
| Common Mistake | Using indices in casual writing | Using indexes in formal academic papers |
Natural Examples
Here are examples showing how each plural fits into real writing situations.
Example 1: Business Email (Casual)
“Hi Mark, can you double-check the indexes in the customer database? A few seem to be missing.”
Using indexes here sounds natural and professional without being stiff.
Example 2: Financial Report (Formal)
“The major stock indices in Asia closed higher today, led by the Nikkei and Hang Seng.”
Indices is the standard term in finance. Using indexes here would mark you as an outsider.
Example 3: Academic Paper
“The study calculated diversity indices for each ecosystem sample.”
In ecology and other sciences, indices is the expected form.
Example 4: Technical Documentation
“The database administrator rebuilt all table indexes overnight to improve query performance.”
In computing, indexes is the dominant form, though indices is also understood.
Common Mistakes
Even experienced writers make errors with these plurals. Here are the most frequent problems.
Mistake 1: Using Indices in Casual Writing
Wrong: “I need to update the indices in my spreadsheet.”
Better: “I need to update the indexes in my spreadsheet.”
Unless you are in a formal context, indexes sounds more natural.
Mistake 2: Using Indexes in Formal Academic Work
Wrong: “The study used several diversity indexes to compare habitats.”
Better: “The study used several diversity indices to compare habitats.”
In academic writing, indices shows you know the conventions of your field.
Mistake 3: Mixing Both in the Same Document
Wrong: “The market indexes rose, but the economic indices fell.”
Better: Choose one form and stick with it throughout your document unless you have a specific reason to switch. If you are writing a financial report, use indices consistently.
Mistake 4: Thinking One Is Always Wrong
Some learners believe indexes is incorrect because it is not the Latin form. This is not true. Both are standard English. The key is context, not correctness.
Better Alternatives and When to Use Them
Sometimes you can avoid the choice altogether by using a synonym. This is useful when you are unsure of your audience or want to keep your writing simple.
- List: Use for a simple ordered set of items. “Please check the list of customers.”
- Table of contents: Use for a book or report. “The table of contents is on page 3.”
- Catalog: Use for a collection of items. “The product catalog is online.”
- Directory: Use for a list of files or contacts. “The directory contains all employee names.”
- Record: Use for a single entry. “Each record in the database has a unique ID.”
These alternatives are especially helpful in spoken English, where indexes and indices can sound awkward.
Mini Practice: Test Your Knowledge
Choose the correct plural for each sentence. Answers are below.
- In a casual email to a coworker: “Please update the database ______.”
a) indexes
b) indices - In a financial report for investors: “The market ______ showed a recovery.”
a) indexes
b) indices - In a scientific paper: “We calculated diversity ______ for each site.”
a) indexes
b) indices - In a conversation with a friend: “I fixed the ______ in my spreadsheet.”
a) indexes
b) indices
Answers:
- a) indexes – Casual email calls for the standard plural.
- b) indices – Financial reports use the formal Latin plural.
- b) indices – Academic writing prefers the traditional form.
- a) indexes – Conversation sounds natural with the regular plural.
Frequently Asked Questions
1. Is it ever wrong to use “indexes”?
No. Indexes is a standard English plural. It is only considered inappropriate in very formal academic or financial writing where indices is the expected form. In all other contexts, indexes is perfectly fine.
2. Can I use “indexes” and “indices” in the same document?
It is best to choose one and use it consistently. Mixing them can confuse readers or make your writing seem inconsistent. If you must switch (for example, quoting a source), make sure the reason is clear.
3. Which plural is more common in British English?
Both forms are used in British English, but indices is more common in academic and financial writing there than in American English. In everyday British conversation, indexes is still the norm.
4. What about the verb “index”? Does it change?
No. The verb to index follows regular conjugation: index, indexes, indexed, indexing. For example: “She indexes the reports every month.” The verb form never becomes indices.
Final Advice for Learners
When you write, think about your reader and the setting. If you are sending a quick email or talking to a colleague, use indexes. If you are writing a formal paper or a financial analysis, use indices. The most important rule is consistency. Once you choose a form, stick with it throughout your document. This small attention to detail will make your writing clearer and more professional.
For more guidance on tricky plurals, visit our Confusing Plurals section. You can also explore Common Plural Forms or check our Plural Spelling Rules for other helpful patterns. If you have questions, see our FAQ or contact us.
