Appendices or Appendixes: What’s the Correct Plural of Appendix?

Ever stared at the end of a book or research paper wondering whether it should say “appendices” or “appendixes”? You’re not alone! This is one of those tricky English plural rules that leaves many students, teachers, and even seasoned professionals scratching their heads. If you’ve ever searched “Is it appendices or appendixes?” or “What’s the correct plural of appendix?”, you’re definitely in the right place.

In English, some words have more than one correct plural form, and appendix is one of them. But here’s the catch: while both “appendices” and “appendixes” are technically correct, they aren’t always used in the same way. That’s where this post comes in — to help you understand which is right, when to use it, and why it matters. Whether you’re a high school student writing your first research report, a college learner polishing up a thesis, or a teacher guiding young writers, this quick guide will give you clarity and confidence in your spelling.

What Does “Appendix” Mean?

The word “appendix” has two primary meanings in English:

1. Anatomy – A small pouch attached to the lower end of the human large intestine.
   
2. Writing and Publishing – A section at the end of a document or book containing extra information, references, or detailed explanations that support the main text.

Here’s how each is used:

• Medical context:
  “The patient had his appendix removed due to inflammation.”
  
• Academic context:
  “See Appendix B for the complete research data.”
  

So far, so good. But how do you make it plural?

Origins and Etymology of “Appendix”

Understanding the roots of the word helps explain the confusion.

• “Appendix” comes from Latin, where the plural is “appendices.”
• Over time, English developed a more naturalized plural form, “appendixes.”

Both plural forms are grammatically correct in modern English, but they serve different purposes based on field, tone, and context.

Appendices vs Appendixes: What’s the Real Difference?

Let’s settle the debate with a clear comparison.

Plural Form	Usage Context	Tone/Field
Appendices	Academic, formal, written work	Publishing, education, research
Appendixes	Casual, anatomical, general writing	Medicine, biology, informal contexts

Appendices is more formal and often used in writing and scholarly work.
Appendixes is more common in medical or casual writing.

“Use appendices when referring to documents. Use appendixes for body parts.”

Singular of Appendices or Appendixes

No matter which plural form you use, the singular remains the same: appendix.

You’ll never say “an appendice” or “an appendex.”

Examples:

• “This book includes an appendix of references.”
  
• “The doctor found that the appendix was swollen.”

Simple rule: Always use “appendix” for singular.

When to Use “Appendices”

Use appendices when referring to documents, academic content, or supporting materials in books, research papers, or reports.

Examples Where Appendices Is Preferred:

• Textbooks
• Thesis papers
• Legal documents
• Corporate reports
• Scientific publications

Real-world example:

“The report includes three appendices that detail budget breakdowns, graphs, and technical specifications.”

This form is also supported by academic style guides, which we’ll explore shortly.

When to Use “Appendixes”

Use appendixes when referring to multiple anatomical appendices, or in informal contexts where the Latin form feels out of place.

Medical Example:

“Multiple inflamed appendixes were documented in the study on intestinal disorders.”

This version is more natural in healthcare, biology, or conversational writing.

In casual writing or speech, some people also prefer appendixes just because it sounds simpler or more familiar.

Style Guide Recommendations and Institutional Preferences

Here’s what major style guides say about which plural to use:

Style Guide	Preferred Plural	Notes
APA (American Psychological Association)	Appendices	Use for documents and academic works
MLA (Modern Language Association)	Appendices	Formal, scholarly tone
Chicago Manual of Style	Appendices	Consistent with Latin origin
AMA (American Medical Association)	Appendixes	Used in medical writing and anatomy contexts
Oxford English Dictionary	Both	Both forms accepted, depending on context
Merriam-Webster	Both	Appendices (documents), Appendixes (body)

In summary:

• Use appendices for books and reports.
  
• Use appendixes for biology and anatomy.

Industry-Specific Usage: A Comparison Table

Here’s how different fields apply the plural form:

Industry/Field	Preferred Plural	Example Sentence
Academic Writing	Appendices	“All supporting data is included in the appendices.”
Medical Field	Appendixes	“The surgeon removed two inflamed appendixes.”
Business Reports	Appendices	“Refer to the appendices for annual financial details.”
Casual Blog Writing	Appendixes	“You’ll find a few helpful appendixes at the end.”

Examples in Real Contexts

From Academic Work:

“Refer to Appendices A–D for the full dataset and survey results.”
(Excerpt from a PhD thesis in psychology)

From a Medical Journal:

“Cases with duplicated appendixes are rare but clinically significant.”
(Journal of Gastrointestinal Surgery)

From Business Documentation:

“The detailed project plan and stakeholder charts are included in the appendices.”
(Company Annual Report, 2024)

These real-world examples confirm that context drives choice.

Common Mistakes to Avoid

1. Using the wrong plural in the wrong context.
   Don’t write “appendices” when talking about surgery!
   
2. Mixing both forms in one document.
   Choose one and stay consistent.
   
3. Using plural when singular is needed.
   If there’s only one section or organ, stick with appendix.
   
4. Capitalizing unnecessarily.
   Only capitalize “Appendix” if you’re referencing a titled section (e.g., Appendix A).

FAQs: Quick Answers for Busy Readers

Is “appendices” the only correct plural of appendix?

No. Both are correct. “Appendices” is used in academic and publishing contexts. “Appendixes” is used in anatomy or informal writing.

Can I use “appendixes” in a research paper?

Technically yes, but “appendices” is preferred and more professional.

Are “appendices” ever used in anatomy?

No. For human body parts, the plural is always “appendixes.”

Why does appendix have two plural forms?

It comes from Latin roots, where “appendices” was the original plural. English later adopted “appendixes” as a more naturalized option.

Which plural does APA recommend?

APA style recommends using appendices for all academic and research content.

Final Verdict: Which Plural Should You Use?

Here’s your golden rule:

• Use appendices when referring to documents, sections, or books.
• Use appendixes when referring to anatomy or in informal conversation.
• Be consistent within the same document or body of work.

When in doubt, follow the style guide that matches your field.

Bonus: Memory Trick to Remember the Right Plural

Here’s an easy way to lock it in:

• Appendices = Academic
• X in Appendixes = X-ray (medicine)

This little mnemonic will help you always pick the correct version on the fly.

Conclusion

So, what’s the final word — “appendices” or “appendixes”? The answer depends on what you’re writing and how formal your tone is. If you’re working on an academic paper, writing a research report, or preparing a thesis, go with “appendices” — it’s the preferred plural form in formal writing. On the other hand, if you’re writing something more casual or technical, “appendixes” is perfectly acceptable too.

The key is to stay consistent. Don’t mix the two in the same document, and always match the tone of your writing. Whether you’re a student learning English grammar, a teacher explaining tricky plural rules, or just someone who searched “Is it appendices or appendixes?”, you now know exactly when and how to use each form.

Remember, English can be weird — but with a little clarity, you can master even the most confusing parts. Keep learning, keep asking questions, and you’ll keep growing as a confident communicator.