Introduction

Have you ever been confused about whether to use “appendices” or “appendixes”? You’re not alone. Many writers struggle with this plural form because both spellings are correct but serve different purposes.

 “Appendices” follows the Latin pluralization and is commonly used for supplementary sections in books and reports. “Appendixes,” on the other hand, aligns with standard English pluralization and is mainly used in anatomical contexts.

This article explores the difference between these terms, provides usage examples, and helps you determine the right word for your writing.

What Is an Appendix?
An appendix is supplementary material added at the end of a book, research paper, thesis, or report. It contains extra information that supports the main content but is not essential to understanding the primary argument.

 By placing this material in an appendix, writers keep their main text clear and focused while still providing readers with valuable reference material.

In the field of anatomy, the appendix refers to a small, tube-like organ attached to the large intestine. Although it has no vital function in the human body, it can become inflamed, leading to appendicitis—a condition requiring surgical removal.

Common Types of Appendices in Writing:

• Data tables and figures – Charts, graphs, or statistics that provide in-depth analysis.
  Example: A study on climate change might include temperature data trends spanning several decades.
• Additional research details – Extended explanations or background information.
  Example: A legal report may include historical case law that influenced its findings.
• Interview transcripts – Full records of interviews conducted for research.
  Example: A sociology thesis could contain complete conversations with participants on social behavior.
• Survey results – Raw data and responses from questionnaires.
  Example: A marketing report might include customer feedback on product preferences.

Here’s a more detailed explanation of the plural forms “appendices” and “appendixes”:

“The word ‘appendix’ has two acceptable plural forms: ‘appendices’ and ‘appendixes.’ Both are grammatically correct, but the choice between them depends on how formal or technical you want to be.

• Appendices: This form follows Latin pluralization rules. Since ‘appendix’ comes from Latin, it’s common in academic, scientific, and technical writing to use ‘appendices.’ This version sounds more formal and is often preferred in scholarly contexts.
• Appendixes: This form follows the regular English pluralization rule, where you simply add ‘es’ to the end of the word. It’s more commonly used in casual writing and is perfectly acceptable in everyday language.

In short, both ‘appendices’ and ‘appendixes’ are correct, but ‘appendices’ is typically chosen for formal or professional writing, while ‘appendixes’ works well for more informal use.”

Why Do We Have Two Plural Forms?

The word appendix comes from Latin. Many Latin-based words in English have two plural forms. Words like index and matrix also have this variation:

• Latin Pluralization: index → indices, matrix → matrices, appendix → appendices
• English Pluralization: index → indexes, matrix → matrixes, appendix → appendixes

Both versions exist because language evolves over time.

When to Use “Appendices”

The plural form “appendices” is most commonly used in formal, academic, and professional writing. It’s the preferred choice in many style guides and is generally used when referring to supplementary materials in books, research papers, reports, and other scholarly work.

• Academic and Research Writing: If you’re writing a research paper, thesis, or dissertation, appendices is the standard plural form used to refer to sections where additional data, charts, tables, or other supporting materials are placed. For example, you might include a detailed table of data in the appendix, which would be referred to as “Appendix A” or “Appendices” when there’s more than one.
• Style Guides: Most major style guides like APA (American Psychological Association), MLA (Modern Language Association), and Chicago all recommend using “appendices” when citing or listing more than one supplementary section. These guides follow the traditional Latin pluralization rules, which is why they lean towards appendices rather than appendixes.
• Books and Scholarly Publications: If you’re working on a book, particularly a nonfiction or academic one, appendices is the preferred choice. It’s seen as more formal and consistent with scholarly norms, especially when the book has multiple sections or large volumes of supplementary material.
• Consistency: When you’re working in formal writing, especially in research or scholarly papers, using appendices throughout ensures consistency. Whether you’re citing supplementary information or referring to sections of your work, it’s important to stick to one form for clarity and professionalism.

Example Sentences:

• “The book includes three appendices for additional reading.”
• “The study’s findings are detailed in the appendices.”

When to Use “Appendixes”

While “appendices” is the standard plural form in academic and professional contexts, “appendixes” is the preferred plural form in certain situations, especially in more informal or specialized contexts.

• Medical Terminology: In the medical field, appendixes is commonly used to refer to multiple anatomical appendices (i.e., the small, tube-shaped organs attached to the large intestine). For example, when discussing cases of appendicitis (inflammation of the appendix), doctors and researchers may refer to appendixes if they’re talking about multiple cases or multiple appendages.

Example: “In rare cases, patients may have multiple appendixes, a condition known as accessory appendices.”

• Informal Writing: Outside of formal academic or scholarly writing, appendixes is perfectly acceptable in more casual or non-technical contexts. For instance, if you’re writing a blog post or article that’s not deeply academic, using appendixes might feel more natural to your readers. It follows the regular pluralization rule in English, making it easier to use in informal settings.
• Non-Latin Contexts: In contexts where you’re not sticking strictly to Latin-based formalities, such as journalism or casual writing, appendixes is just a simpler, more intuitive option. It’s easy to form and often feels less stiff than the more traditional Latin-derived appendices.
• Preference in English: In standard English, especially in conversational settings, appendixes might be the form you’re more familiar with. People are more likely to use this plural form when talking about additional materials (like appendices in a book) in day-to-day language, as it follows the standard rule of adding -es for plural.

Example Sentences:

• “Some people have extra appendixes in their bodies.”
• “The doctor studied the functions of different appendixes.”

Appendices vs. Appendixes in Different Style Guides

Style guides provide rules for formal writing. Here’s what major guides recommend:

Style Guide	Preferred Plural
APA (American Psychological Association)	Appendices
MLA (Modern Language Association)	Appendices
Chicago Manual of Style	Appendices
Common Informal Writing	Appendixes
Medical Usage	Appendixes

Writers should follow the preferred spelling of their chosen style guide.

Common Mistakes and Misconceptions

Many people think one version is incorrect. However, both are right. The key is consistency. Pick one form and use it throughout your document.

Examples in Context

To clarify the difference, here are examples of both words in sentences:

Appendices in Writing:

• “The appendices contain detailed charts and graphs.”
• “Three appendices provide background information.”

Appendixes in Anatomy:

• “He researched cases of inflamed appendixes.”
• “Scientists studied the function of appendixes in mammals.”

Quick Reference Table: Appendices vs. Appendixes

Feature	Appendices	Appendixes
Pluralization Style	Latin-derived	English adaptation
Used in	Books, research papers	Anatomy, informal writing
Style Guide Preference	APA, MLA, Chicago	Less common
Example Sentence	“The appendices contain data tables.”	“He has two appendixes.”

Final Verdict: Which One Should You Use?

If you’re writing a book, academic paper, or report, use appendices. If you’re referring to body parts, use appendixes. Consistency is the most important rule.

Conclusion

Both appendices and appendixes are correct, but their usage depends on context. Academic and professional writers should stick to appendices, while medical or casual writers may use appendixes when discussing anatomy. Choose wisely and stay consistent.

FAQs

1. Is appendices the correct plural of appendix?
Yes, appendices is correct for academic and book writing.

2. Can I use appendixes instead of appendices?
Yes, but appendixes is mostly used in medical or informal writing.

3. Do style guides prefer appendices?
Yes, APA, MLA, and Chicago all recommend appendices.

4. Are appendices and appendixes interchangeable?
Grammatically, yes, but usage depends on the subject matter.

5. Why do some words have two plural forms?
English borrows from Latin and adapts words differently over time.