Plural of Appendix: Appendices vs Appendixes Explained Simply

Language often presents puzzles that appear small at first glance but become intriguing once you look closer. One such puzzle involves the word appendix.

Is the plural appendices or appendixes? Both forms exist, and both are considered correct, but they do not always appear in the same settings. Understanding why requires a look at history, grammar, and how English absorbs words from other languages.

Why Does Appendix Have Two Plural Forms?

The word appendix comes from Latin, where words ending in -ix often formed plurals ending in -ices. That is why appendices developed as the original plural. Over time, English speakers adapted the word to their own patterns. Since English usually adds -es to form plurals, appendixes emerged as a natural variant.

In modern usage, appendices tends to be more common in formal writing, especially academic, scientific, and medical contexts. Appendixes appears more often in general English and informal writing. Both are correct, but your choice may depend on your audience and subject matter.

How Do Dictionaries Treat the Plural of Appendix?

Leading dictionaries such as Merriam-Webster, Oxford English Dictionary, and Cambridge English Dictionary list appendices and appendixes as acceptable plurals.

Some note that appendices is preferred when referring to supplementary material in books or documents, while appendixes may be used more often in medical references, though even there both are recognized.

This shows that English does not always follow a single rule but often allows parallel forms. Linguistic research confirms that such variation arises when borrowed words keep their original forms while also adapting to English norms.

When Should You Use Appendices?

Appendices works best in formal, academic, or professional settings. It is the expected plural when referring to additional sections at the end of books, reports, or theses.

Examples:

The research paper included three appendices containing survey data.
Please review the appendices at the end of this manual for safety guidelines.
The dissertation had detailed appendices with charts and maps.
All references were listed in the appendices following the bibliography.

When Should You Use Appendixes?

Appendixes is more commonly used in everyday language or when the context is medical. It often appears in textbooks for younger learners, magazines, or health-related discussions.

Examples:

Several patients had their appendixes removed due to appendicitis.
The surgeon explained how inflamed appendixes can become dangerous.
In biology class, we studied the structure of human appendixes.
The disease was rare but affected multiple appendixes across a family group.

A Quick Visual Guide

Here is a simple chart to help you choose the right form:

Usage Context	Preferred Plural	Example Sentence
Academic papers	Appendices	The appendices provide further explanation of the statistical models.
Technical manuals	Appendices	See appendices A and B for installation instructions.
Medical references	Appendixes	Doctors removed several infected appendixes last year.
Everyday conversation	Appendixes	Two of my friends had their appendixes taken out as teenagers.
Literature and publishing	Appendices	All maps and charts appear in the appendices at the back of the book.

How Does History Shape This Difference?

Linguists and historians of English point out that words like index (indices/indexes), matrix (matrices/matrixes), and appendix reflect a pattern. English borrowed these terms from Latin, kept their classical endings in certain fields, and simplified them in others.

Research by university linguists shows that fields like mathematics and science are more likely to preserve Latin forms, while general English leans toward simplified endings.

This explains why appendices has a scholarly tone, while appendixes feels more straightforward. The same distinction exists with other Latin-derived words, showing how English balances heritage and practicality.

Why Do Style Guides Differ?

Major style guides acknowledge both plurals but sometimes recommend one over the other.

The Chicago Manual of Style suggests using appendices in formal documents.
The American Medical Association Manual allows appendixes in medical contexts.
Academic publishers often insist on appendices for book supplements.

This variation shows that the “correct” choice often depends not on grammar alone but on the tradition of the field.

Do People Use Both Interchangeably?

Yes, in everyday conversation many people use the two forms interchangeably without much thought. However, in writing, especially in school or professional work, readers may expect consistency. If you start with appendices, continue using that form throughout your text. If you prefer appendixes, stick with it.

Can Appendix Ever Be Counted Differently?

The word appendix has two main meanings:

A section at the end of a document.
A small organ in the human body.

The meaning often decides which plural feels natural. For books, appendices dominates. For medical organs, appendixes often appears. But again, both forms are correct.

Extended Examples in Context

Academic example:
A university professor assigns a thesis and requires that students place raw data in the appendices rather than the main body.

Medical example:
A surgeon at a teaching hospital lectures about cases where multiple appendixes showed unusual growths.

Everyday example:
A student writing a report on biology might mix both: “My teacher said the paper must include an appendix, but I read that people also have appendixes inside their bodies.”

Publishing example:
A novelist includes fictional maps and timelines as appendices at the end of a fantasy book.

Frequently Asked Questions

Is appendices always more correct than appendixes?

No. Both are correct. Appendices is more formal and common in scholarly writing, while appendixes is widely used in general and medical contexts.

Do British and American English treat the plural differently?

Usage patterns are similar in both varieties. British English may lean slightly more toward appendices in publishing, while American English shows higher tolerance for appendixes, especially in everyday speech.

Can I use both forms in the same document?

It is better to choose one form and remain consistent. Switching between them in one piece of writing may confuse readers.

Why does English keep Latin endings at all?

English borrowed heavily from Latin during the Middle Ages and Renaissance. Many words kept their classical forms in science, law, and academia because these fields valued precision and tradition. Over time, English simplified other words, which is why we see dual forms.

Which plural should I use in a business report?

Use appendices, since business, academic, and legal writing often prefer the formal form.

Is the plural of appendix ever irregular in other languages?

Yes. In Latin, the plural is strictly appendices. Other European languages influenced by Latin often follow similar patterns. English is unusual in allowing two accepted plurals.

Do style choices affect SEO or digital publishing?

Yes. Online searches show that both terms appear in user queries, but appendices is more frequent in academic search databases. Using both terms thoughtfully in digital writing can help reach broader audiences.

Final Thoughts

The plural of appendix reflects English’s dual nature: a language that respects its Latin roots while also simplifying for everyday use. Appendices signals tradition, scholarship, and formality.

Appendixes reflects natural adaptation and practical use. Knowing when to choose one or the other helps writers communicate more clearly, whether preparing a medical journal article, a school paper, or a company manual.

By understanding the context, respecting consistency, and recognizing both forms as correct, you can use the plural of appendix confidently. This small detail not only improves grammar but also sharpens the professionalism of your writing.

Plural of Appendix: Appendices vs Appendixes Explained Simply