Appendix or Appendices — Singular vs Plural Explained Simply

Many people feel confident while writing a report, assignment, research paper, or book—until they reach the final pages. That’s when a simple question often causes confusion:

should you write appendix or appendices? This small choice can feel stressful, especially in academic or professional writing where correctness matters.

People search for “appendix or appendices” because English does not always follow simple plural rules. Most words just add -s, but appendix changes its form in a different way.

Students worry about marks, professionals worry about credibility, and writers want to sound polished. The confusion becomes even bigger when people hear appendixes and wonder if that is also correct.

This article solves that problem clearly and completely. You will get a quick answer, learn the origin of the words, understand British and American English usage, and see real-life examples.

You’ll also learn which spelling to use based on your audience and how to avoid common mistakes. By the end, you’ll know exactly when to use appendix and when to use appendices—with confidence.

Appendix or Appendices – Quick Answer

Appendix is singular.
Appendices is the standard plural form.

Simple examples:

This report has one appendix.
The thesis includes three appendices.

In informal English, appendixes is sometimes used, but appendices is preferred in formal writing.

The Origin of Appendix or Appendices

The word appendix comes from Latin. It is based on the word appendere, which means to attach or to add. In Latin grammar, many words ending in -ix form their plural by changing to -ices.

That is why:

appendix → appendices
index → indices
matrix → matrices

English borrowed these words and kept their original plural forms, especially in academic and scientific writing. Over time, English also created simpler plurals like appendixes, but these are less formal.

The spelling difference exists because English mixes rules from many languages, especially Latin.

British English vs American English Spelling

There is no spelling difference between British and American English for appendix or appendices. Both use the same forms.

The real difference is about style and formality, not country.

Form	British English	American English	Example
Appendix	✔ Yes	✔ Yes	See Appendix A
Appendices	✔ Preferred	✔ Preferred	Refer to Appendices B–D
Appendixes	Rare	Informal	Software appendixes

In universities and official documents, both UK and US prefer appendices.

Which Spelling Should You Use?

Your audience matters.

US audience: Use appendix (one) and appendices (more than one)
UK / Commonwealth: Same rule applies
Academic or global audience: Always use appendices
Casual or technical writing: Appendixes may be acceptable

Professional tip: If your writing is formal, academic, or legal, always choose appendices.

Common Mistakes with Appendix or Appendices

❌ This document has two appendix
✅ This document has two appendices

❌ Please see the appendixes in my thesis
✅ Please see the appendices in my thesis

❌ Appendices is attached (when only one exists)
✅ Appendix is attached

❌ Appendix are listed below
✅ Appendices are listed below

Appendix or Appendices in Everyday Examples

Email:
Please find the appendix attached for reference.

News:
The investigation includes several appendices with evidence.

Social Media:
Check the appendix for extra details.

Formal Writing:
Supporting charts are provided in Appendices A and B.

These examples show how the words change based on number and tone.

Appendix or Appendices – Google Trends & Usage Data

Search trends show that “appendix or appendices” is most popular in:

The United States
United Kingdom
Australia
Academic regions worldwide

The term appendices appears more often in:

Research papers
Theses and dissertations
Legal and government documents

Appendixes appears mainly in:

Technical manuals
Software documentation
Informal writing

This shows that appendices is the dominant and trusted form.

Appendix vs Appendices – Comparison Table

Feature	Appendix	Appendices
Number	Singular	Plural
Formality	Formal	Very formal
Academic use	Yes	Yes (preferred)
Informal alternative	No	Appendixes
Common context	One extra section	Multiple extra sections

FAQs: Appendix or Appendices

1. Is appendices grammatically correct?
Yes. It is the standard plural of appendix.

2. Can I use appendixes instead of appendices?
Yes, but only in informal or technical writing.

3. Which form should I use in a thesis?
Always use appendices.

4. Is appendix singular or plural?
Appendix is singular.

5. Do British and American English use different spellings?
No. Both use the same forms.

6. Can one document have both words?
Yes. One appendix, many appendices.

7. Does appendix also mean a body organ?
Yes, and its plural is also appendices.

Conclusion

The confusion between appendix or appendices comes from English borrowing rules from Latin. Once you understand the basic rule, the choice becomes simple.

Use appendix when you are talking about one extra section. Use appendices when there are two or more.

In both British and American English, appendices is the preferred plural form in formal, academic, and professional writing. While appendixes exists, it is best saved for informal or technical contexts.

If you want your writing to sound clear, correct, and professional, appendices is the safest option.

Whether you are a student, researcher, or professional, using the correct form improves clarity and credibility. Remember the simple rule: one appendix, many appendices. Follow this, and you’ll never hesitate again.