What’s the Plural of Appendix: Understanding Variations in English Usage

Appendix, Appendices, Appendixes — See the Pattern

Look at these sentences. Can you see what changes?

• Please read the appendix at the end of the book.
• This textbook has three appendices with extra information.
• The doctor removed five appendixes last month.
• Check the appendix for the full list of words.

Did you see the pattern? When you talk about one, you say appendix. When you talk about more than one, you can say appendices or appendixes — but the right choice depends on what you are talking about.

When to Use Appendices and When to Use Appendixes

Both appendices and appendixes are correct. The difference is simple:

• Appendices — use this when you talk about extra sections in books, reports, or documents. This is the most common form.
• Appendixes — use this when you talk about the body part (the small organ near your stomach). Doctors and nurses prefer this form.

Why two forms? Because appendix comes from Latin. The Latin plural is appendices (the ending -ix changes to -ices). But in modern English, we also just add -es to make appendixes. Both are correct — it just depends on what you mean.

Easy way to remember: If you are talking about a book, use appendices. If you are talking about a body part, use appendixes. When you are not sure, appendices is the safer choice — most people will understand it in any situation.

Real-Life Examples With Appendix, Appendices, and Appendixes

• The textbook has two appendices with grammar tables. (extra sections in a book)
• My teacher asked us to read the appendix before the exam. (one extra section)
• The surgeon has removed over 200 appendixes in her career. (the body part, more than one)
• All the appendices in the report contain useful data. (sections in a report)
• His appendix was inflamed, so the doctor removed it. (one body part)

You are doing great. Now let us look at the mistakes many learners make.

Two Mistakes to Avoid With Appendix

Even advanced learners mix up appendices and appendixes sometimes — so if you find this confusing, you are not alone. Here are two common mistakes:

Mistake 1: Writing “appendixs”

Some learners try to add just -s to appendix. But words ending in -x need -es, not just -s.

Mistake 2: Using “appendixes” when talking about books

While appendixes is not wrong, it sounds unusual when you are talking about documents. Most readers expect appendices in that context.

How to remember: Think of “appendices” as the “book word” and “appendixes” as the “body word.” If you are writing about a book, use the book word.

Other words that work the same way: index → indexes/indices, matrix → matrixes/matrices, vertex → vertexes/vertices.

Test Yourself: Appendix, Appendices, or Appendixes?

Choose the correct answer for each sentence. Click Check to see if you are right.

Keep Going — You Are Building Something

You just learned the plural of appendix. That is one more tricky Latin word you will never get wrong again.

But here is a question: what about index? You might think it works the same way — and it does, mostly. But there is one important difference in when to use each plural form that surprises most learners.

Next lesson: What’s the Plural of Index?

Sources

1. Synonyms of appendix.
2. Sentence examples of appendices.
3. Origin of appendix.