Appendices or Appendixes? The Complete, Authoritative Guide

Sometimes the simplest questions create unexpected challenges, and when choosing between Appendices or Appendixes the decision often feels harder than it should because writers balance clarity and usage in everyday work.

When I first faced this choice in real research writing, I saw how origins, linguistic habits, and historical patterns shape the way these words move through academic language. The pull between traditional forms and modern preferences often creates gentle confusion, yet it also offers a chance to think more deeply about why each appendix appears in an article. Over time, I realized that understanding the context, the practical applications, and the meanings behind each option can quietly demystify a decision that once seemed heavier than it really was.

In my own writing life, I found that stepping back to look at my work made the decision easier. Academic research usually favors appendices, while simpler guides use appendixes because the flow feels more natural to readers. Still, the real turning point came when I noticed how my personal style, small daily habits, and awareness of clarity shaped my choices. Each time I paused over this tiny puzzle, I became more confident, and that quiet confidence helped me stay consistent without overthinking whether one form carried more weight than the other.

Quick Summary: Appendices or Appendixes?

Here’s the short version so you can breathe easy:

• Both “appendices” and “appendixes” are correct plural forms of “appendix.”
• Appendices is the traditional plural, directly inherited from Latin.
• Appendixes is the modern, regular English plural, formed by adding -es.
• Writers often choose appendices for formal or academic documents.
• The medical field uses both but leans slightly toward appendixes in general English contexts.
• Both forms appear in dictionaries, style guides, and academic resources.

If you only remember one thing: context—not correctness—determines which plural you should choose.

What “Appendix” Actually Means

Core Definitions

The word appendix comes from the Latin appendere, meaning to hang upon or to attach. That meaning survived intact for over 2,000 years. Whether you’re discussing the small organ inside the human body or the extra material at the back of a book, the core idea stays the same: an appendix is something attached.

The English language uses appendix in two major ways:

• Textual appendix — supplementary material added to the end of a document.
• Anatomical appendix — the small, tube-like organ near the junction of the small and large intestine.

Those are the two realms where our plural confusion begins.

Why One Word Has Two Distinct Uses

Linguists consider appendix a “polysemous” word, meaning it holds several related meanings. Over centuries scholars kept the Latin root intact for academic writing because Latin dominated education. Meanwhile ordinary English speakers evolved toward easier, more predictable plural forms. Those diverging habits created two accepted plurals in modern English.

Appendix in Books, Academic Reports, and Technical Documents

Purpose of a Textual Appendix

When you’re reading a book, whitepaper, research report or technical manual, the appendix sits quietly at the end. It’s not decorative. It’s a holding space for material that’s important but too bulky to fit comfortably inside the main text.

A textual appendix may include:

• extended datasets
• supplementary charts
• methodology explanations
• additional case studies
• full interview transcripts
• legal disclosures
• formulas
• maps
• diagrams
• glossary-style lists

When there’s more than one, writers label them Appendix A, Appendix B, Appendix C, and so on.

Here’s the key: academic and publishing industries overwhelmingly prefer the Latin plural “appendices.” It simply looks more polished in formal contexts.

How Style Guides Treat the Plural

Different style guides have clear preferences:

Style Guide	Preferred Plural	Notes
APA 7	appendices	Used for all academic manuscripts
Chicago Manual of Style	appendices	Considered standard in publishing
MLA Handbook	appendices	Matches classical spelling
Associated Press (AP)	appendixes	AP supports modern English spellings

If you’re writing for school, academia or publishing, appendices is the safe default. If you’re writing for journalism or general readers, appendixes is completely acceptable.

Appendix in Anatomy and Medical Science

What the Anatomical Appendix Is

In medicine the appendix refers to the vermiform appendix, a narrow, finger-like tube extending from the cecum.The anatomical appendix appears in:

• medical textbooks
• surgery notes
• biological research
• radiology reports
• emergency care documentation

While both plurals exist, clinicians often default to appendixes when speaking casually. Medical textbooks, however, frequently use appendices because they follow classical terminology.

Accepted Medical Plural Forms

Both forms show up in medical literature:

• “Inflamed appendices were observed…”
• “CT imaging revealed multiple appendixes…”

Medical professionals choose based on the tone of the text. Academic research tends to prefer appendices, while everyday clinical communication leans toward appendixes because it aligns with English plural norms.

The Linguistic Divide: Textual vs Anatomical Plurals

Where the Usage Split Originated

For hundreds of years, scholars wrote almost everything in Latin. That habit survived in early English academic writing so words like index → indices, matrix → matrices, and appendix → appendices. Over time English began simplifying these forms, giving us indexes, matrixes, and appendixes as alternatives.

English never fully committed to one direction. Instead it kept both the classical and modern plurals.

The Practical Rule Writers Should Follow

A simple rule of thumb helps you choose instantly:

• Use “appendices” for formal writing, academic documents, and book sections.
• Use “appendixes” for general English or informal writing where tradition matters less.

Either choice is valid. What matters is consistency within a document.

Singular Form: Understanding “Appendix”

Before choosing a plural, it helps to understand how the singular behaves across fields.

You’ll see appendix used in:

• publishing (extra materials in books)
• education (supplementary info in dissertations)
• science (structures attached to organs)
• law (supporting documents)
• engineering (detailed specs or diagrams)

Because the singular is identical in all fields, the plural distinction can feel artificial—but that’s the nature of English. Rules evolve in different pockets of culture.

How Pluralization Works

Classical (Latin) Plural: Appendices

Latin nouns ending in -ix (appendix, index, radix) often pluralize to -ices.

Examples:

• appendix → appendices
• index → indices
• codex → codices

This form appears extensively in academia.

Modern English Plural: Appendixes

Modern English simplifies many plurals by adding -es to words ending in sibilant sounds.

Examples:

• box → boxes
• matrix → matrixes
• appendix → appendixes

Most dictionaries label appendixes as fully correct, though slightly more informal.

Current Usage Trends

A quick comparison using data from the Corpus of Contemporary American English shows:

• appendices appears more often in academic and technical writing.
• appendixes appears more often in journalism, popular science and general reading material.

English embraces both without controversy.

When to Use Each Correct Form

Use Appendices When:

• writing formal papers
• publishing a book
• creating a thesis or dissertation
• labeling multiple supplemental sections
• preparing corporate technical reports
• following guidelines from APA, MLA or Chicago
• you want writing that ⁠feels polished or scholarly

Use Appendixes When:

• writing blog posts or general-interest content
• producing informal reports
• explaining anatomy to non-specialists
• following AP style
• aiming for simpler language
• you prefer modern English grammar

Industry-Specific Preferences

Industry	Preferred Plural	Why
Academia	appendices	Matches traditional linguistic expectations
Publishing	appendices	Standard in book formatting
Journalism	appendixes	AP style uses modern plural forms
Medicine	both	Depends on formality level and publication

These differences explain why you’ll see both in everyday life.

Origins and Evolution of the Word “Appendix”

Etymological Breakdown

The journey of appendix starts with:

• Latin appendere = “to hang on”
• Latin appendix = “something attached”

The earliest English records of appendix date back to the 16th century. Scholars adopted the word for book materials and later for anatomy.

How the Word Shifted Across Fields

The word evolved along two tracks:

1. Scholarly Latin Track
   Used primarily in academia, leading to the plural appendices.
2. Everyday English Track
   Speech and informal writing began using appendixes because it follows intuitive spelling patterns.

Why the Dual Plural Survived

English is a “borrowing language.” It absorbs words from Latin, French, Greek, German, Norse and dozens of others. Instead of flattening everything into one grammar system, English keeps variations as long as they stay useful.

That’s why both plural forms remain alive today.

Here’s a short timeline:

Century	Event
1500s	Appendix enters English through academic writing
1600–1700s	Latin plural “appendices” becomes standard in scholarship
1800s	Anatomical meaning grows in popularity
1900s	Regular plural “appendixes” spreads in journalism and general English
2000s–today	Dictionaries recognize both equally

English kept both because they serve different audiences.

Read More: Suing or Sueing? The Correct Spelling, Meaning and Rules

Real-World Examples of Each Form

Appendix (Singular)

• “See Appendix A for raw survey data.”
• “The appendix becomes inflamed during appendicitis.”
• “The engineering appendix contains wiring diagrams.”

Appendices (Plural – Documents)

• “The report includes three appendices with full methodology notes.”
• “Tables and charts appear in the final appendices.”
• “Researchers placed additional documents in the accompanying appendices.”

Appendices (Plural – Anatomy)

• “The dissection revealed abnormalities in two appendices.”
• “Comparative anatomy shows that several mammals have vestigial appendices.”

Appendixes (Plural – Modern/Informal)

• “The surgeon examined both appendixes during the procedure.”
• “The textbook lists several appendixes with extra exercises.”
• “The article ends with two short appendixes summarizing the data.”

Key Takeaways

• Both plurals are 100% correct.
• Appendices is formal, traditional, academic.
• Appendixes is modern, simple, conversational.
• Choose based on audience, tone, and style guide.
• Be consistent inside your document

Here’s a quick reference table:

Form	Field	Tone	Best Use
Appendices	Academic, Books, Research	Formal	High-level writing
Appendixes	Journalism, Everyday English	Neutral/Informal	General clarity
Both	Medical	Depends on publication	Clinical writing

FAQs:

Can “appendices” and “appendixes” both be used in formal writing?

Yes. Appendices is preferred in formal writing but appendixes isn’t wrong. Some scientific journals use one and some use the other. Always match your audience or style guide.

Which plural form does APA or Chicago prefer?

Both the APA and Chicago Manual of Style prefer appendices.

Is “appendixes” considered informal?

Slightly, but not incorrect. Many dictionaries list it as equal in correctness.

Is the plural different in British vs American English?

Not significantly. Both English varieties accept both forms. Academic writing in both regions leans toward appendices.

Can a document contain multiple appendices?

Absolutely. Large reports often include several appendices labeled A, B, C and so on.

Why does English allow two plurals for one word?

English merges classical Latin grammar with modern English patterns. When both remain useful, both survive.

Conclusion:

Choosing between appendices and appendixes may seem like a small detail, yet it carries real weight in writing. Once you understand the history behind both forms and see how context shapes their use, the decision becomes much easier. Instead of feeling puzzled by the difference, you start to recognize how each term fits naturally depending on the tone, purpose, and expectations of your work.

Over time, the choice begins to feel less like a linguistic puzzle and more like a practical step toward clearer communication. When you pause, look at your writing needs, and consider your audience, the right form usually reveals itself. Whether you lean toward tradition or prefer simpler modern patterns, both options help you communicate with clarity and confidence.