Is Appendix Singular or Plural?

The word appendix is singular. It refers to one item, such as a section at the end of a book or the small organ attached to the large intestine. When you need to talk about more than one, the plural can be either appendices or appendixes. Both forms are correct, but they are used in different contexts. Appendices is more common in academic and formal writing, while appendixes is often used in medical or general contexts.

Quick Answer

Appendix is singular. The plural forms are appendices (preferred in formal and academic writing) and appendixes (common in medical and everyday use). Choose based on your audience and tone.

Understanding the Singular Form

When you use appendix as a singular noun, it follows standard English rules. You would say one appendix or an appendix. This is straightforward and rarely causes confusion.

• The book has an appendix at the end.
• I need to check one appendix for the report.
• Her appendix was removed last year.

Why Two Plurals?

The reason appendix has two accepted plurals comes from its Latin origin. Many English words borrowed from Latin keep their original plural ending (-ices) while also developing an English-style plural (-es). This is similar to words like index (indices or indexes) and matrix (matrices or matrixes).

When to Use Appendices

Appendices is the traditional Latin plural. It is the standard choice in academic papers, legal documents, textbooks, and formal reports. If you are writing a thesis, a business proposal, or a scholarly article, use appendices.

• Please refer to the appendices for the raw data.
• The appendices contain all supporting documents.
• Each chapter has its own set of appendices.

Tone: Formal. Suitable for professional emails, academic writing, and official publications.

When to Use Appendixes

Appendixes is the English-style plural. It is more common in medical contexts (when referring to the body part) and in general, everyday writing. If you are writing a blog post, a casual email, or a medical chart, appendixes is perfectly acceptable.

• The surgeon removed both appendixes during the operation.
• I found two appendixes in the old manual.
• Most people have only one appendix, but some have two appendixes.

Tone: Neutral to informal. Suitable for conversation, medical notes, and less formal writing.

Comparison Table: Appendices vs. Appendixes

Natural Examples

Here are examples showing how appendix and its plurals appear in real writing and conversation.

• Academic context: The appendices at the back of the thesis contain all the interview transcripts.
• Medical context: The doctor said both appendixes were inflamed and needed surgery.
• Book context: This novel has an appendix that explains the historical background.
• Email context (formal): Please see the appendices attached to this email for the full budget breakdown.
• Conversation context: I had to look in the appendixes of the user guide to find the troubleshooting section.

Common Mistakes

Even advanced English learners sometimes make errors with this word. Here are the most frequent mistakes and how to avoid them.

• Mistake: Using appendi as a singular form.
  Correct: The singular is always appendix. There is no such word as appendi.
• Mistake: Writing appendices when referring to the body part in a medical chart.
  Better: Use appendixes for the body part to sound natural. Appendices is not wrong, but it can sound overly formal in a medical setting.
• Mistake: Using appendix as a plural.
  Correct: Appendix is only singular. For plural, use appendices or appendixes.
• Mistake: Confusing appendix with index.
  Note: An appendix contains supplementary material, while an index lists topics and page numbers. They are different parts of a book.

Better Alternatives and When to Use Them

Sometimes you may want to avoid the plural confusion altogether. Here are some alternatives that work in specific situations.

• Use “supplementary material” instead of appendices in very formal academic writing. Example: The supplementary material is available online.
• Use “addendum” (plural: addenda) when referring to a single addition to a document. Example: Please see the addendum for the updated figures.
• Use “back matter” when talking about all the sections at the end of a book, including the appendix. Example: The back matter contains the glossary and the appendix.
• Use “extra sections” in casual conversation. Example: The report has a few extra sections at the end.

When to use it: Choose these alternatives when you want to be very clear or when your audience may not be familiar with the word appendix. In most cases, however, using appendices or appendixes correctly is the best approach.

Mini Practice: Check Your Understanding

Test yourself with these four questions. Answers are below.

1. Which is the correct singular form? (a) appendi (b) appendix (c) appendices
2. You are writing a formal research paper. Which plural should you use? (a) appendixes (b) appendices (c) both are equally good
3. You are a doctor writing a medical report about two patients. Which sentence is correct? (a) Both patients had their appendices removed. (b) Both patients had their appendixes removed. (c) Both are correct, but (b) is more natural.
4. True or false: Appendix can be used as a plural noun.

Answers

1. (b) appendix
2. (b) appendices
3. (c) Both are correct, but (b) is more natural.
4. False. Appendix is always singular.

Frequently Asked Questions

1. Is it ever correct to write “appendi”?

No. Appendi is not a word in English. The singular is always appendix. Some learners mistakenly drop the x, but this is an error.

2. Can I use “appendices” for the body part?

Yes, you can, but it is less common. In medical writing, appendixes is more typical. If you use appendices for the body part, it may sound overly formal or academic. Stick with appendixes for medical contexts.

3. Which plural is more common in everyday English?

Appendices is more common overall because it appears frequently in books and formal documents. However, in everyday conversation, many people use appendixes without thinking about it. Both are acceptable.

4. How do I remember the difference?

Think of appendices as the “academic” plural (both words start with a) and appendixes as the “everyday” plural. Another trick: appendixes has an e like English, so it follows English plural rules.

For more help with similar questions, visit our Singular or Plural Checks section. You can also explore Common Plural Forms for other tricky words. If you have further questions, check our FAQ page or contact us directly.