Have you ever written indexes and wondered whether indices would be better? Both spellings are correct, but they are not equally common in every field.
The word you choose may depend on whether you are writing about books, mathematics, databases, or the stock market.
The good news is that you do not need to guess. Once you understand how these plural forms work, you can use them with confidence in everyday writing and technical documents.
Quick Answer:
Both indexes and indices are correct plural forms of index. Use either when referring to more than one index, but consider the context.
- Indexes is common in general English, book reference lists, and computing.
- Indices is common in mathematics, statistics, and scientific writing.
- Both forms appear in financial writing and other technical fields.
For example:
- The book contains several indexes.
- The students learned the rules of indices.
- The database uses multiple indexes.
- Investors watched several stock market indices.
Neither form is always better. Choose the one that fits your subject and follow the terminology of your preferred style guide or publication.
What Does Index Mean?
An index is a list, number, reference, or measure that helps people find information or understand something. Its meaning changes with the context.
Here are four common uses:
- Books: An alphabetical list of topics, names, or terms that directs readers to relevant pages.
- Mathematics: A number or symbol that identifies a position or indicates a power.
- Databases: A structure that helps a computer find records more efficiently.
- Finance: A measure that tracks the performance of a selected group of stocks or other assets.
For example, a textbook may have an index at the back, while a database may use an index to speed up searches.
An investor, meanwhile, may follow a market index to understand how a group of stocks is performing.
When you need to refer to more than one, both indexes and indices are possible plural forms.
Why Are There Two Plural Forms of Index?
Most English nouns form their plurals by adding -s or -es. For example, book becomes books, and box becomes boxes.
The word index follows this regular pattern to form indexes. It also has the traditional Latin-derived plural indices, which remains common in modern English.
Both forms have become established, so you do not need to treat one as a mistake.
Other words also have two accepted plural forms:
| Singular | Plural forms |
|---|---|
| Index | Indexes, indices |
| Appendix | Appendixes, appendices |
| Matrix | Matrixes, matrices |
| Vertex | Vertexes, vertices |
These pairs do not always have the same preferences in every field. For example, indices is familiar in mathematics, while indexes is widely used in computing and publishing.
The main rule is simple: use the plural that suits your context, not the one that looks more complicated.
When to Use Indexes
Use indexes when it sounds natural for your subject. It is a familiar choice in everyday English and is widely used for book references, computer systems, and databases.
Indexes in Books and Publishing
A book index helps readers find specific information without searching every page. It often lists topics alphabetically and gives the page numbers where they appear.
Examples:
- The editor checked the indexes before approving the books for publication.
- Both volumes contain detailed indexes.
- The librarian used the indexes to locate information about ancient history.
In these sentences, indexes is a natural choice because the focus is on reference lists.
Do not confuse an index with a table of contents. A table of contents lists the main sections of a work, usually in their order of appearance. An index helps readers locate particular topics, names, or terms.
Indexes in Databases
In database terminology, indexes is widely used for structures that help systems locate stored information.
Examples:
- The administrator created indexes for frequently searched columns.
- The database uses several indexes to improve query performance.
- The developer removed unused indexes to reduce storage overhead.
A database index can make certain searches faster, but it also uses storage and may add work to data changes. This is why database administrators must choose indexes carefully.
Although indices can also appear in technical discussions, indexes is a familiar choice in database documentation.
Indexes in Programming
Programmers often use index to refer to an item’s position in a sequence or to describe a data structure used for searching.
Examples:
- The program checks the indexes before accessing the elements.
- The developer found an error in the array indexes.
- These indexes help the application locate matching records.
The best wording can depend on the programming language and the documentation you follow. Do not assume that every programming community uses only one plural form.
When to Use Indices
Use indices when it fits the established language of your subject. It is especially common in mathematics, statistics, and scientific writing.
However, it is not automatically more formal or more correct than indexes. The choice should help readers understand your meaning.
Indices in Mathematics
In mathematics, indices is a familiar term, especially when discussing powers. In some mathematical contexts, an index can also identify a position or distinguish one variable from another.
Examples:
- The teacher explained the laws of indices.
- The equation contains indices that identify different variables.
- Students practised simplifying expressions involving indices.
In British mathematical terminology, indices is particularly familiar when referring to powers. In other mathematical contexts, the appropriate wording depends on the concept being discussed.
Indices in Statistics and Science
Researchers use indices to summarize measurements, compare groups, or track changes over time.
Examples:
- The researchers compared several economic indices.
- The report examined price indices across different regions.
- Scientists used environmental indices to assess changes in local conditions.
Here, indices fits the terminology commonly found in these fields. Still, indexes may also be correct when it is the established form in a particular publication or system.
The important point is to use the correct technical term and keep it consistent throughout your work.
Indexes or Indices in American and British English?
Both forms are used in American and British English. It is not accurate to say that indexes is exclusively American or that indices is exclusively British.
The difference is more closely linked to subject matter and established usage.
| Context | Common usage |
|---|---|
| General English | Indexes |
| Book reference lists | Indexes |
| Database systems | Indexes |
| Mathematics | Indices |
| Scientific writing | Indices and indexes |
| Stock market reporting | Both forms |
These are general tendencies, not strict rules. You can use indices in American English and indexes in British English without making a grammatical error.
If you are writing for a specific publication, check its style guide. If no preference is given, choose the form that sounds natural in your context and use it consistently.
Indexes or Indices in Python?
In Python, an index refers to the position of an item in a sequence, such as a list, tuple, or string. Python uses zero-based indexing,
which means the first item has index 0, the second has index 1, and each following item increases by one.
Both indexes and indices are correct plural forms of index. In everyday programming discussions, indexes is a natural choice when referring to item positions.
Indices is also common in mathematical and scientific contexts, especially when discussing arrays, matrices, and multidimensional data.
For example:
- Indexes: The program uses two indexes to access items in a list.
- Indices: The algorithm uses multiple indices to identify elements in a matrix.
Both forms are acceptable in Python-related writing. Choose the form that best suits your context and use it consistently throughout your documentation.
Indexes or Indices in the Stock Market?
Both stock market indexes and stock market indices are correct. Financial publications use these terms to describe measures that track selected groups of stocks.
Three major US stock market benchmarks are:
- Dow Jones Industrial Average: Tracks 30 prominent US companies.
- S&P 500: Tracks approximately 500 leading US companies.
- Nasdaq Composite: Covers thousands of securities listed on the Nasdaq Stock Market.
You may see these called the three major stock market indexes or the three major stock market indices.
For example:
- Investors followed the major stock market indexes during the trading session.
- Several global indices fell after the economic announcement.
Both forms are correct. The wording depends on the publication or financial source.
Remember that these benchmarks measure different groups of securities, so their performance may differ even on the same trading day.
Heat Indexes or Indices?
Both heat indexes and heat indices can be understood as plural forms of heat index. The heat index describes how hot the air feels when humidity is considered alongside air temperature.
In everyday US weather reporting, heat index is the familiar term, and heat indexes is a natural plural.
Examples:
- The weather report compared heat indexes across several cities.
- Officials warned residents that the heat index could reach dangerous levels.
Heat indices may also appear in technical or scientific writing. When preparing a weather report, follow the terminology used by the relevant meteorological authority.
Indexes or Indices in Legal Writing?
In legal writing, both forms may be appropriate when referring to multiple indexes or reference lists. The preferred form can depend on the jurisdiction, court, legal publisher, or document type.
Examples:
- The clerk reviewed the indexes of court records.
- The researchers examined several legal indices.
For contracts, legal briefs, and court filings, follow the relevant institution’s style requirements. Do not assume that indices is required simply because the document is formal.
Indexes vs. Indices: Examples in Everyday Sentences
These examples show how both forms work in different situations.
Using indexes:
- The encyclopedia contains several indexes for quick reference.
- The librarian updated the indexes after adding new books.
- The database uses indexes to retrieve information efficiently.
- The developers checked the array indexes for errors.
- Investors compared the major stock market indexes.
Using indices:
- The mathematician explained the rules of indices.
- Researchers compared several economic indices.
- The report measured price changes using different indices.
- The equation contains indices that identify its variables.
- Scientists evaluated environmental indices from several regions.
These examples reflect common usage rather than exclusive rules. Either plural can work in some contexts where the other is more common.
Common Mistakes to Avoid
Choosing between indexes and indices is straightforward once you avoid these common errors.
Assuming one form is incorrect. Both are accepted plurals of index. Do not reject either one simply because you are more familiar with the other.
Treating them as strictly American or British. Both forms occur in both varieties of English. Subject-specific conventions are a better guide.
Thinking indices is always more formal. It is common in mathematics and science, but indexes is also suitable for professional and academic writing.
Changing forms without a reason. If you use indexes throughout a database guide, do not switch to indices without a clear purpose. Consistency helps readers follow your explanation.
Confusing an index with a table of contents. A table of contents lists the main sections of a document. An index directs readers to specific subjects, names, or terms.
FAQs
Are indices the same as indexes?
Yes. Both are plural forms of index. They can have the same meaning, although some subjects and publications prefer one form over the other.
How do you pluralize an index?
You can write indexes or indices. Choose the form that suits your context and follow any relevant style guide.
What are the three major stock market indexes?
Three major US stock market benchmarks are the Dow Jones Industrial Average, the S&P 500, and the Nasdaq Composite. These are also commonly called stock market indices.
What does indices mean?
Indices is the plural of index. Depending on the context, it can refer to reference lists, mathematical quantities, database structures, or numerical measures.
Do you say indexes or indices?
Both are correct. Indexes is common in general English and computing, while indices is common in mathematics and scientific writing.
What does indexes mean?
Indexes means more than one index. It can refer to multiple reference lists, database structures, or measures used to track information.
What does index mean?
An index is a list, reference, number, or measure that helps people locate information or understand something. Its exact meaning depends on the subject.
What is another word for an index?
Depending on the context, alternatives include list, catalog, directory, indicator, and measure. These words are not exact synonyms in every situation.
How do you pronounce indices?
Indices is commonly pronounced IN-duh-seez. The exact pronunciation may vary slightly by accent.
Conclusion
Both indexes and indices are correct plural forms of index. The best choice depends on your subject, audience, and preferred style guide. Use indexes naturally in general writing, publishing, and database discussions.
Choose indices when it fits the conventions of mathematics, statistics, or scientific writing. Both forms also appear in financial contexts.
You do not need to follow a strict American-versus-British rule. Focus on clear meaning, natural wording, and consistency throughout your writing.
