What Is the Plural of Appendix?

The word appendix has two standard plural forms: appendices and appendixes. Both are correct, but they are used in different contexts. Appendices is the traditional Latin plural and is preferred in academic, scientific, and formal writing, especially when referring to supplementary material at the end of a book or document. Appendixes is the regular English plural and is more common in medical, informal, and everyday contexts, particularly when referring to the body part (the vermiform appendix).

Quick Answer

• Appendices – Use for supplementary sections in books, reports, or academic papers (formal).
• Appendixes – Use for the body part or in less formal writing (medical or general).
• Both are acceptable in most situations, but your audience and tone should guide your choice.

Understanding the Two Plurals

The reason appendix has two plurals comes from its history. The word entered English from Latin, where it followed a specific declension pattern. Over time, English speakers also applied the regular -es ending. Today, both forms are widely recognized, but they carry different stylistic and contextual weights.

When to Use “Appendices”

Appendices is the go-to choice for formal writing. You will see it in academic papers, legal documents, technical manuals, and books. If you are writing a research paper, a thesis, or a business report, appendices signals that you are following standard scholarly conventions.

Example: “The report includes three appendices with supporting data.”

Context: Use this in formal emails, academic submissions, or professional documents. It sounds precise and authoritative.

When to Use “Appendixes”

Appendixes is the regular English plural. It is common in medical writing, casual conversation, and general usage. If you are talking about the body part, appendixes is the standard term. It also appears in less formal documents or when the writer wants to avoid a Latin-sounding word.

Example: “The surgeon removed both appendixes during the operation.”

Context: Use this in everyday conversation, patient notes, or informal emails. It feels natural and straightforward.

Comparison Table: Appendices vs. Appendixes

Natural Examples

Here are examples showing how each plural fits into real writing and speech.

• Formal email: “Please review the appendices attached to the proposal before our meeting.”
• Medical report: “The patient’s appendixes showed no signs of inflammation.”
• Academic paper: “The appendices contain the full survey results.”
• Casual conversation: “I had to look in the appendixes at the back of the book.”
• Technical manual: “See the appendices for installation diagrams.”

Common Mistakes

Even experienced writers sometimes mix up these forms. Here are the most frequent errors and how to avoid them.

• Mistake: Using “appendices” when talking about the body part.
  Correct: “The surgeon removed both appendixes.” (Not “appendices” for body parts.)
• Mistake: Using “appendixes” in a formal academic paper.
  Correct: “The appendices provide additional context.” (Stick with “appendices” for formal documents.)
• Mistake: Writing “appendi” or “appendicies” as a plural.
  Correct: The plural is either “appendices” or “appendixes.” There is no shortened form.
• Mistake: Assuming one form is always wrong.
  Correct: Both are valid. Choose based on context, not on a false rule.

Better Alternatives and When to Use Them

If you are unsure which plural to use, consider these alternatives or strategies.

• Use “supplementary materials” – This works well in formal writing when you want to avoid the Latin plural entirely. Example: “The supplementary materials are in the back of the book.”
• Use “addendum” (singular) or “addenda” (plural) – These are common in legal and publishing contexts. Example: “The addenda clarify the contract terms.”
• Rephrase the sentence – If the plural feels awkward, you can often reword. Instead of “Check the appendices,” say “Check the additional information at the end.”
• Match your audience – For a general audience, “appendixes” is safer. For a scholarly audience, “appendices” is expected.

Mini Practice: Test Your Understanding

Choose the correct plural for each sentence. Answers are below.

1. The book has two _______ at the end. (appendices / appendixes)
2. During the surgery, the doctor removed one of his _______. (appendices / appendixes)
3. Please include all relevant _______ in your report. (appendices / appendixes)
4. In casual conversation, most people say _______. (appendices / appendixes)

Answers: 1. appendices (formal context), 2. appendixes (body part), 3. appendices (formal report), 4. appendixes (casual speech).

Frequently Asked Questions

1. Is “appendices” the only correct plural?

No. Both “appendices” and “appendixes” are correct. “Appendices” is the traditional Latin plural, while “appendixes” follows regular English rules. Your choice depends on context and formality.

2. Can I use “appendixes” in a research paper?

It is possible, but not recommended. Most academic style guides prefer “appendices” for formal writing. Check your institution’s guidelines, but “appendices” is the safer choice.

3. What is the plural of “appendix” in medical terms?

In medical contexts, “appendixes” is standard when referring to the body part. For example, “The patient had two appendixes.” However, some medical journals still use “appendices” for consistency with Latin forms.

4. How do I remember which plural to use?

Think of the context. If you are writing about a book or document, use “appendices.” If you are talking about the body or having a casual conversation, use “appendixes.” This simple rule covers most situations.

Final Note

Choosing between appendices and appendixes is not about right or wrong—it is about matching your word to your situation. For formal, academic, or technical writing, appendices is the standard. For medical, informal, or everyday use, appendixes works perfectly. By understanding the nuance, you can write with confidence and clarity.

For more help with plural forms, visit our Common Plural Forms section. If you have questions, check our FAQ or contact us. You can also review our editorial policy for how we ensure accuracy.