Appendix Plural Form: Rule, Examples, and Mistakes

If you are writing a medical report, a research paper, or even an email about a book, you might need the plural of appendix. The direct answer is that appendix has two correct plural forms: appendices and appendixes. The choice depends on the context. In medical and academic writing, appendices is the standard plural. In general or informal English, appendixes is also acceptable and becoming more common. This guide explains the rule, gives you practical examples, and helps you avoid common mistakes.

Quick Answer: What Is the Plural of Appendix?

Use appendices for formal, medical, or academic writing. Use appendixes for everyday conversation, emails, or less formal contexts. Both are grammatically correct, but they carry different tones.

Why Are There Two Plurals?

The word appendix comes from Latin. In Latin, nouns that end in -ix often change to -ices in the plural. This is why appendix becomes appendices. Over time, English speakers also started using the regular English plural rule (adding -es), which gave us appendixes. Both forms are now accepted, but they are used in different situations.

When to Use Appendices

Use appendices in formal writing, especially in medicine, science, law, and academia. This form follows the traditional Latin rule and is considered more precise and professional.

Medical Context

In medicine, appendix refers to the small pouch attached to the large intestine. When a doctor talks about more than one appendix (for example, in a patient with a rare anatomical variation), they almost always say appendices.

• Natural example: The CT scan revealed two appendices in the patient, a rare congenital condition.
• Natural example: During the surgery, the team removed both inflamed appendices.

Academic and Book Context

In books, reports, and research papers, appendices refers to the supplementary sections at the end. This is the standard term in academic style guides.

• Natural example: Please refer to the appendices for the full data tables.
• Natural example: The appendices include the survey questions and raw responses.

When to Use Appendixes

Use appendixes in everyday English, informal emails, and general conversation. This form follows the regular English plural rule and sounds more natural to many native speakers in casual settings.

• Natural example: I added the charts in the appendixes at the end of the document.
• Natural example: The book has three appendixes with extra recipes.

Email and Conversation Context

If you are writing a quick email to a colleague, appendixes is perfectly fine. It sounds less stiff and more direct.

• Natural example (email): Hi Mark, I attached the appendixes for the project report. Let me know if you need anything else.
• Natural example (conversation): I checked the appendixes, but I couldn’t find the map you mentioned.

Comparison Table: Appendices vs. Appendixes

Common Mistakes with the Plural of Appendix

Mistake 1: Using “Appendices” in Every Informal Situation

Some learners think appendices is always the “correct” form. This is not true. In a casual email or conversation, appendices can sound overly formal or even pretentious.

• Incorrect: I put the extra notes in the appendices. (In a quick chat with a friend)
• Correct: I put the extra notes in the appendixes.

Mistake 2: Using “Appendix” as a Plural

Never use appendix to refer to more than one. This is a common error among English learners.

• Incorrect: The report has three appendix.
• Correct: The report has three appendices.
• Correct: The report has three appendixes.

Mistake 3: Confusing “Appendices” with “Appendicitis”

Appendicitis is the inflammation of the appendix, not a plural form. Do not mix them up.

• Incorrect: The doctor removed two appendicitis.
• Correct: The doctor removed two appendices.

Better Alternatives and When to Use Them

If you are unsure which form to use, consider these alternatives and guidelines:

• In a medical journal or research paper: Always use appendices. It is the standard and expected form.
• In a business email to a client: Use appendixes for a neutral, professional tone that is not too stiff.
• In a textbook or style guide: Use appendices to follow academic conventions.
• In a blog post or social media: Use appendixes to sound natural and approachable.

When in doubt, appendices is the safer choice for any formal or written context. For spoken English, appendixes is more common and less likely to sound awkward.

Mini Practice: Test Your Understanding

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

1. The surgeon removed two inflamed ______ during the operation.
   a) appendix
   b) appendices
   c) appendixes
2. Please check the ______ at the end of the user manual for troubleshooting tips.
   a) appendix
   b) appendices
   c) appendixes
3. In an informal email to your coworker, which form sounds more natural?
   a) appendices
   b) appendixes
4. The academic paper includes three ______ with supporting data.
   a) appendix
   b) appendices
   c) appendixes

Answers

1. b) appendices – Medical context requires the formal Latin plural.
2. c) appendixes – A user manual is a general document; appendixes is fine. Appendices is also acceptable but more formal.
3. b) appendixes – Informal email calls for the regular English plural.
4. b) appendices – Academic writing prefers the traditional form.

Frequently Asked Questions (FAQ)

1. Is “appendices” the only correct plural?

No. Both appendices and appendixes are correct. The choice depends on the context. Appendices is standard in formal and medical writing, while appendixes is common in everyday English.

2. Can I use “appendix” as a plural in any situation?

No. Appendix is always singular. Using it as a plural is a grammatical mistake. Always add -es or change the ending to -ices for the plural.

3. Which plural is more common in British English?

In British English, appendices is more common in academic and medical writing. However, appendixes is also used and accepted. The trend is similar in American English, though appendixes may be slightly more common in general American usage.

4. How do I pronounce “appendices” and “appendixes”?

Appendices is pronounced /əˈpɛndɪsiːz/ (uh-PEN-di-seez). Appendixes is pronounced /əˈpɛndɪksɪz/ (uh-PEN-dik-siz). The main difference is the ending: -seez vs. -siz.

Final Note

Understanding the plural of appendix is about matching the form to the situation. Use appendices for formal, medical, and academic writing. Use appendixes for informal, general, and conversational English. Both are correct, and knowing when to use each will make your English sound more natural and precise. For more help with plural forms, visit our Plural Spelling Rules section or explore Confusing Plurals for similar words. If you have further questions, check our FAQ page.