Appendix or Appendices? Learn the Correct Form in Seconds

Both “appendix” and “appendices” are correct English words, but they are used differently. Appendix is the singular form, meaning one additional section at the end of a book, report, or document. Appendices is the plural form, meaning two or more such sections.

For example, if a research paper contains one supplementary section, you can call it an appendix. If it contains three supplementary sections, you can call them appendices.

These words are common in academic writing, research papers, books, medical contexts, and formal reports. The confusion often comes from the unusual plural ending, which differs from the familiar pattern of adding s or es to a noun.

Understanding the difference will help you use both words correctly in essays, professional documents, and everyday writing.

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Quick Answer

• Appendix: Singular form; refers to one supplementary section or, in anatomy, a small organ attached to the large intestine.
• Appendices: Plural form; refers to multiple supplementary sections or, in anatomy, multiple appendix organs.

Examples:

• Please read the appendix at the end of the report.
• The research paper includes three appendices.

Both spellings are correct. Use appendix for one and appendices for more than one.

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What Does Appendix Mean?

Appendix is a noun with two common meanings. In books and documents, it refers to supplementary material placed at the end. In anatomy, it refers to the small, finger-shaped pouch attached to the large intestine.

Appendix in Books and Documents

An appendix provides additional information that supports the main content without interrupting its flow.

It may contain:

• Detailed tables or charts.
• Research questionnaires.
• Extra data and statistics.
• Technical explanations.
• Supporting documents.
• Additional examples or calculations.

Examples:

1. The author included an appendix with the survey results.
2. You can find the full questionnaire in the appendix.
3. The appendix provides additional information about the experiment.
4. The report contains an appendix explaining the calculations.
5. Refer to the appendix for further details.

Appendix in Anatomy

In anatomy, the appendix is a small pouch connected to the beginning of the large intestine.

Example: The doctor explained the symptoms associated with an inflamed appendix.

The context determines which meaning is intended.

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What Does Appendices Mean?

Appendices is the plural form of appendix. It refers to two or more supplementary sections in documents or to multiple appendix organs in anatomical contexts.

Appendices in Books and Documents

When a report or book contains several supplementary sections, appendices is a correct plural form.

Examples:

1. The dissertation includes three appendices.
2. The appendices contain additional research data.
3. Please review the appendices before submitting the report.
4. Each appendix is listed separately in the table of contents.
5. The final chapter refers readers to the appendices.

Appendices in Anatomy

The word can also refer to more than one anatomical appendix, although this usage is less common in everyday conversation.

Example: The medical report discussed the anatomical differences observed in the appendices of the specimens.

In ordinary medical writing about one person, appendix is generally the form you will encounter.

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Appendix vs Appendices: Key Differences

Feature	Appendix	Appendices
Grammatical number	Singular	Plural
Meaning in documents	One supplementary section	Two or more supplementary sections
Meaning in anatomy	One appendix organ	Multiple appendix organs
Example	Read the appendix.	Read the appendices.
Correct spelling	Yes	Yes

The key difference is singular versus plural. Both forms are correct, but they cannot always be substituted for one another.

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Why Is the Plural of Appendix Appendices?

The word appendix comes from Latin. Its traditional Latin plural is appendices, which is why this form is common in formal and academic English.

However, English also allows the regular plural appendixes.

Both appendices and appendixes are accepted plural forms of appendix. In formal academic writing, appendices is especially common when referring to supplementary sections in books, research papers, and reports.

Appendices vs Appendixes

Singular	Plural	Usage
Appendix	Appendices	Traditional plural, common in formal writing
Appendix	Appendixes	Regular English plural, also correct

Example with appendices: The report contains two appendices.

Example with appendixes: The book’s appendixes contain extra reference material.

If you want a conventional choice for an academic document, appendices is a reliable option. The most important thing is to use one plural form consistently throughout your document.

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Common Mistakes to Avoid

Mistake 1: Using Appendix for Multiple Sections

Incorrect: The report contains three appendix.

Correct: The report contains three appendices.

You can also write “three appendixes,” because that plural form is accepted.

Mistake 2: Treating Appendices as Singular

Incorrect: The appendices contains the survey results.

Correct: The appendices contain the survey results.

Appendices is plural, so it normally takes a plural verb.

Mistake 3: Assuming Appendixes Is Always Wrong

Incorrect claim: Appendixes is never correct.

Correct explanation: Both appendices and appendixes are accepted plurals of appendix.

Mistake 4: Confusing an Appendix With a Footnote

An appendix is a supplementary section, usually placed at the end of a document. A footnote is a brief note typically placed at the bottom of a page.

They serve different purposes.

Mistake 5: Using the Plural When There Is Only One

Incorrect: Please see the appendices at the end of the report, when the report contains only one such section.

Correct: Please see the appendix at the end of the report.

Always match the noun to the number of sections you mean.

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Everyday Examples of Appendix and Appendices

Here are examples showing how to use both forms correctly.

Academic Writing

• Appendix: The appendix contains the research questionnaire.
• Appendices: The appendices contain the supporting data and interview questions.

Business Reports

• Appendix: An appendix provides a detailed breakdown of expenses.
• Appendices: The appendices include financial tables and technical notes.

Books

• Appendix: The author added an appendix to explain unfamiliar terms.
• Appendices: The appendices at the end of the book contain additional references.

Medical Contexts

• Appendix: The patient underwent surgery to remove the appendix.
• Appendices: The textbook discusses the appendices in its anatomical examples.

Instructions and References

• Appendix: Refer to Appendix A for the complete list.
• Appendices: Refer to Appendices A and B for the complete lists.

These examples show how the correct form depends on if you mean one item or several.

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Appendix or Appendices in Academic Writing

In academic papers, dissertations, and research reports, appendices usually contain supporting material that would make the main discussion too long or difficult to follow.

A document with one supplementary section may label it Appendix A. A document with several may use Appendix A, Appendix B, and Appendix C, while referring to the collection as the appendices.

For example:

• “See Appendix A for the questionnaire.”
• “The appendices provide additional research data.”

When preparing an academic document, follow the required style guide or your institution’s formatting instructions. Some guides have specific rules for appendix headings, numbering, and references.

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British vs American English

Both appendix and appendices are used in British and American English. The alternative plural appendixes is also accepted in both varieties.

Feature	American English	British English
Singular	Appendix	Appendix
Traditional plural	Appendices	Appendices
Regular plural	Appendixes	Appendixes
Spelling difference	None	None

There is no major British-American spelling difference between these forms. Your choice should depend on the number of items and the style guide you are following.

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Easy Trick to Remember the Difference

Use this simple memory rule:

• Appendix = one.
• Appendices = more than one.

Think of the word index and its traditional plural indices. The pattern is similar: appendix becomes appendices in the traditional plural form.

For example:

“One appendix contains the questionnaire.”

“Two appendices contain the questionnaire and the survey results.”

Remember that appendixes is also an accepted plural, so you do not need to treat it as a spelling error.

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Frequently Asked Questions (FAQs)

1. Is appendix or appendices correct?

Both are correct. Appendix is singular, while appendices is plural.

2. What is the plural of appendix?

The two accepted plural forms are appendices and appendixes. Appendices is common in formal and academic writing.

3. Is appendices grammatically correct?

Yes. It is the traditional plural of appendix.

4. Is appendixes also correct?

Yes. Appendixes is an accepted regular English plural.

5. Should I write appendix or appendices in a research paper?

Use appendix for one supplementary section and appendices for multiple sections. Follow your institution’s formatting guidelines.

6. How do you use appendices in a sentence?

Example: “The appendices contain the survey questions and additional data.”

7. Is appendix singular or plural?

Appendix is singular. Its plural forms are appendices and appendixes.

8. Why does appendix become appendices?

The form appendices follows the traditional Latin plural pattern retained in English.

9. Are appendix and appendices spelled differently in British and American English?

No. Both forms are used in British and American English.

10. What is the difference between an appendix and an attachment?

An appendix is usually a supplementary section included at the end of a document. An attachment is a separate item added to a document or message, such as a file attached to an email.

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Conclusion

Appendix and appendices are both correct, but they serve different grammatical purposes. Use appendix when referring to one supplementary section or one anatomical organ.

Use appendices when referring to multiple sections or organs. The alternative plural appendixes is also accepted. For academic papers and formal reports, appendices is a common and suitable choice when you have more than one supplementary section.

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