Appendices or Appendixes: Which Plural Is Correct?

Have you ever finished writing a report or research paper and wondered whether to label its final section Appendices or Appendixes? You’re not alone. Both spellings look unusual, especially if you’re used to adding a simple -s to most English nouns. The good news is that both appendices and appendixes are correct plural forms of appendix. However, one form may fit your writing context better than the other.

The word appendix has two common meanings. It can refer to supplementary material at the end of a document or a small pouch attached to the large intestine. Although both meanings share the same singular spelling, their plural forms sometimes follow different usage patterns.

In academic writing, appendices is especially common when discussing the extra sections of a thesis, dissertation, research paper, or report. Meanwhile, appendixes is a perfectly acceptable alternative and appears in general English and anatomical discussions. Neither spelling is automatically wrong.

Quick Answer

Both appendices and appendixes are correct plurals of appendix. The choice depends on context, convention, and consistency rather than a strict grammatical rule.

Appendices: Often preferred in academic, scientific, and formal documents, especially when referring to supplementary sections.
Appendixes: An accepted English plural that follows the regular spelling pattern of adding -es.
Singular form: Appendix.
US English: Both forms are acceptable.
Best writing tip: Follow your publisher’s, university’s, or organization’s style guide. If no preference exists, choose one form and use it consistently.

Examples:

The dissertation includes three appendices containing survey results and additional tables.
The medical textbook discusses several appendixes and their anatomical features.

Both sentences are grammatically correct. The important thing is to understand your context and follow any relevant editorial conventions.

Comparison Overview

The following table summarizes the main differences between appendices and appendixes.

Feature	Appendices	Appendixes
Singular form	Appendix	Appendix
Grammatical status	Correct plural	Correct plural
Plural formation	Traditional Latin-derived form	Regular English form
Common document usage	Very common in academic and formal writing	Also acceptable
Anatomical usage	Correct	Correct
Accepted in US English	Yes	Yes
Meaning	More than one appendix	More than one appendix
Main recommendation	Often a good choice for formal documents	Suitable when preferred by your style guide

The main difference concerns plural formation and usage preference, not meaning. In most situations, you can use either form without changing what your sentence means.

For instance, a research paper might contain two appendices or two appendixes. In both cases, the phrase refers to two supplementary sections at the end of the paper.

However, choosing one spelling and sticking with it makes your writing look more polished. If your university specifies appendices, don’t alternate between appendices and appendixes in different chapters.

What Does Appendix Mean?

Before comparing the plural forms in greater detail, it helps to understand the word appendix itself. Its meaning depends on the subject you’re discussing.

Appendix as a Supplementary Section

In writing, an appendix is a section at the end of a book, report, academic paper, or other document that provides additional information supporting the main text.

Writers use appendices to include useful details that would interrupt the flow of the main discussion. These sections help readers examine supporting evidence without forcing every technical detail into the body of the document.

For example, a research paper might explain its findings in the main text while placing the complete survey questionnaire in an appendix. Readers who want to examine the questions can consult that section.

Common materials found in document appendices include:

Questionnaires and surveys: The exact questions researchers asked participants.
Supplementary tables: Detailed figures that support the main findings.
Technical calculations: Mathematical steps or statistical procedures.
Research instruments: Interview guides, assessment forms, and measurement tools.
Additional data: Supporting information that doesn’t fit naturally into the main discussion.
Detailed procedures: Instructions or methods that readers may want to review.
Supporting documents: Relevant forms or other materials needed to understand the report.

Consider a student writing a dissertation about online learning. The main chapters might discuss student performance, survey findings, and conclusions. The appendices could contain the full questionnaire, additional statistical tables, and consent forms.

This arrangement keeps the main discussion readable while making important supporting information available.

A document can have one appendix or several. When it contains multiple supplementary sections, writers may label them Appendix A, Appendix B, and Appendix C. The corresponding plural reference is appendices or appendixes, depending on the chosen style.

Appendix as an Anatomical Structure

The word appendix also refers to a small, narrow pouch connected to the cecum, the first part of the large intestine. It sits in the lower-right area of the abdomen, although its precise position can vary between individuals.

The appendix is part of the digestive system. Scientists also recognize that it contains immune tissue and may help maintain populations of beneficial gut bacteria. Its full biological role remains an area of scientific study.

Anatomical writing uses appendix in sentences such as:

The patient’s appendix showed signs of inflammation.
The surgeon examined the appendix during the procedure.
The appendix is attached to the large intestine.

When discussing more than one such structure, both appendices and appendixes are grammatically possible plural forms. Medical publications may favor one spelling according to their terminology and editorial policies.

For example:

The textbook describes several anatomical appendices.
The reference work discusses the structure of different appendixes.

The second sentence isn’t grammatically incorrect simply because it uses the regular English plural. The surrounding publication’s style should guide the final choice.

Main Differences Between Appendices and Appendixes

Although these two spellings mean the same thing, their formation and typical usage deserve a closer look. Understanding the differences will help you make a confident choice in academic, professional, and everyday writing.

Spelling and Plural Formation

English forms most plural nouns by adding -s or -es. For example, book becomes books, while box becomes boxes. However, some nouns have traditional plural forms influenced by Latin or Greek.

The word appendix follows both patterns.

Appendix → Appendices

The form appendices reflects a traditional Latin-derived plural pattern. The ending changes from -ix to -ices. You can see a similar pattern in other English words, including index and indices.

Appendix → Appendixes

The form appendixes follows the regular English approach. Rather than changing the ending to -ices, it retains the original spelling and adds -es.

Here’s a simple comparison:

Singular	Traditional plural	Regular English plural
Appendix	Appendices	Appendixes
Index	Indices	Indexes
Matrix	Matrices	Matrixes
Vertex	Vertices	Vertexes

These examples illustrate a broader feature of English: some nouns accept both traditional and regular plural forms. The preferred form can vary according to the word, subject, and editorial convention.

Importantly, you shouldn’t assume that every word ending in -ix follows exactly the same rules. English plural formation includes several patterns and exceptions.

For appendix, however, both forms are established and correct.

Usage in Academic and Formal Writing

When preparing a dissertation, research paper, or professional report, appendices is often the safest default for supplementary document sections.

Academic writers frequently use this form because it follows a familiar formal convention. Universities, publishers, and professional organizations may also specify it in their formatting guidelines.

Imagine you’re preparing a research report about workplace productivity. Your main chapters explain the research methods, results, and conclusions. At the end, you include the full questionnaire and several supporting tables.

You might write:

The complete questionnaire appears in Appendix A.
Appendix B contains the supplementary statistical tables.
The appendices provide additional evidence supporting the study’s conclusions.

These examples use appendix for one section and appendices for multiple sections.

However, appendixes remains grammatically acceptable in formal writing. Its use doesn’t automatically make a thesis, report, or academic paper incorrect.

The practical question is whether your institution or publisher requires a particular spelling. If it does, follow that requirement. If no rule exists, appendices is a sensible choice for a formal document.

Usage in Medical and Anatomical Contexts

Medical writing also uses both plural forms. Although appendixes may feel more natural to writers who prefer regular English plurals, appendices is also established in anatomical contexts.

Consider these examples:

The report describes inflammation affecting the appendix.
The medical reference discusses the anatomy of the appendix.
The textbook explains the structure of the appendices.

In the first two sentences, appendix refers to a single anatomical structure. In the third, appendices refers to multiple structures or uses the term in a broader anatomical discussion.

A writer could also use appendixes in the third sentence without violating the general plural rule.

One important point deserves attention: the two plural forms don’t represent different anatomical structures. You shouldn’t choose between them based on a belief that one means the digestive organ and the other means a document section.

Instead, check the terminology used by your medical journal, textbook, or organization. Consistency matters more than trying to invent a distinction that standard English doesn’t require.

Pronunciation of Appendices and Appendixes

Spelling isn’t the only feature readers sometimes wonder about. The two plural forms also have slightly different pronunciations.

In US English, appendices is commonly pronounced uh-PEN-duh-seez. Appendixes is commonly pronounced uh-PEN-dik-siz.

The stress falls on the second syllable in both forms.

Word	Approximate US pronunciation	Stress
Appendix	uh-PEN-diks	Second syllable
Appendices	uh-PEN-duh-seez	Second syllable
Appendixes	uh-PEN-dik-siz	Second syllable

These are practical pronunciation guides rather than precise phonetic transcriptions. Individual speakers may vary slightly.

Notice that the ending of appendices sounds different from the ending of appendixes. That difference reflects their spelling patterns.

If you’re giving a presentation about a dissertation, using appendices is perfectly natural. If you say appendixes instead, the word remains correct.

Examples of Appendices in Sentences

The best way to understand a grammar rule is to see it working in context. Because appendices is common in formal writing, you’ll often encounter it in research papers, reports, and academic documents.

Here are several examples.

Academic writing

“The dissertation includes three appendices containing the survey questionnaire, interview guide, and supplementary data.”

This sentence refers to three supporting sections at the end of a dissertation.

Business reports

“The appendices provide the detailed financial calculations used to prepare the annual report.”

Here, the appendices contain supporting information rather than the main conclusions.

Scientific research

“Readers can consult the appendices for the complete experimental procedure and additional results.”

This example shows how supplementary material helps readers examine a study more closely.

Books and reference materials

“The author placed the technical definitions and additional charts in the appendices.”

The plural form refers to multiple sections attached to the main work.

University assignments

“Please review all appendices before submitting your final research paper.”

The writer refers to every supplementary section included in the assignment.

Technical documentation

“The manual’s appendices contain troubleshooting tables and detailed equipment specifications.”

In this case, the supplementary material helps users find technical details without interrupting the main instructions.

Why These Examples Use Appendices

Each sentence refers to additional material attached to a larger document. In these contexts, appendices is a familiar and widely used choice.

However, the examples don’t establish that appendixes would be wrong. You could replace appendices with appendixes in these sentences without changing their basic meaning.

For formal academic work, the key is to use the spelling required by your institution or preferred by your publisher.

Examples of Appendixes in Sentences

The regular plural form appendixes deserves the same attention. It’s a legitimate choice, not a spelling mistake that needs automatic correction.

Here are examples showing how it works.

General writing

“The editor reviewed the appendixes before approving the final manuscript.”

The sentence refers to multiple supplementary sections.

Technical reports

“The appendixes contain detailed specifications that support the main recommendations.”

This example uses appendixes for extra information attached to a report.

Medical reference material

“The chapter discusses the structure and function of the appendixes.”

The plural refers to anatomical structures in the context of the medical discussion.

Instruction manuals

“The appendixes include diagrams that explain the equipment’s internal components.”

The extra diagrams appear in supplementary sections at the end of the manual.

Research documents

“The researcher moved the lengthy calculations into the appendixes to keep the main text concise.”

This sentence demonstrates the regular plural form in an academic context.

Editorial instructions

“Check that the appendixes follow the order established in the table of contents.”

Here, the writer refers to several sections that must appear in a consistent sequence.

Why Appendixes Is Correct

The word follows a straightforward English pattern: add -es to a noun ending in -x when forming its regular plural.

You can see the same pattern in box → boxes and fox → foxes. Although appendix also has a traditional plural form, that doesn’t invalidate the regular alternative.

Think of appendices and appendixes as two accepted routes to the same destination. One preserves a traditional plural pattern, while the other follows a regular English pattern.

Neither route changes the meaning of the word.

Common Mistakes to Avoid

Even though both forms are correct, writers sometimes misunderstand the rule. A few common mistakes can make an otherwise polished document less consistent.

FAQs:

Is Appendices or Appendixes Correct?

Both are correct. Appendices follows a traditional Latin-derived plural pattern, while appendixes follows regular English plural formation. Either form can refer to supplementary document sections or anatomical structures.

Which Is More Common: Appendices or Appendixes?

Appendices is widely used in academic and formal document writing. However, the preferred spelling varies across publications and contexts. A specific style guide may require either form.

Is Appendixes Grammatically Incorrect?

No. Appendixes is an accepted English plural of appendix. It isn’t a misspelling simply because appendices is also correct.

Can Appendices Refer to More Than One Anatomical Appendix?

Yes. Appendices can refer to multiple anatomical structures as well as supplementary document sections. Context determines which meaning the writer intends.

Can Appendixes Refer to More Than One Document Section?

Yes. Appendixes can describe multiple supplementary sections in a book, report, or research paper. The form is grammatically acceptable even when appendices is the preferred spelling in a particular publication.

Conclusion:

The choice between appendices and appendixes is simpler than it first appears. Both are correct plural forms of appendix in US English. The difference lies in their formation and common usage preferences, not in a strict distinction between meanings. Appendices is a popular choice for dissertations, research papers, technical documents, and formal reports. Appendixes is equally valid as an English plural and may suit a publication’s preferred style.