Common Mistakes with the Plural of Appendix

If you are unsure whether to write appendices or appendixes, the direct answer is that both forms are correct, but they are used in different contexts. Appendices is the traditional Latin plural, preferred in academic and formal writing, especially when referring to supplementary material in books or documents. Appendixes is the English plural, more common in medical, technical, or everyday contexts, such as when talking about the human body. Choosing the wrong one can make your writing sound either too stiff or too informal for the situation.

Quick Answer

Use appendices for formal, academic, or book-related content (e.g., “See the appendices in the report”). Use appendixes for medical, scientific, or casual contexts (e.g., “The surgeon removed two appendixes”). Both are acceptable, but knowing your audience helps you sound natural.

Why This Confusion Happens

The word appendix comes from Latin, where the plural ending -ices is standard. However, English speakers often apply the regular -es plural to words that feel familiar. This creates two competing forms. The same pattern appears with words like index (indices vs. indexes) and matrix (matrices vs. matrixes). The choice depends on whether you are following the original Latin rule or the modern English rule.

Comparison Table: Appendices vs. Appendixes

Natural Examples

Using “Appendices” (Formal / Academic)

• “Please review the appendices before the meeting.”
• “The appendices include charts and survey responses.”
• “In the appendices, you will find the full interview transcripts.”
• “The professor asked us to cite the appendices correctly.”

Using “Appendixes” (Medical / Casual)

• “The patient had two appendixes, which is rare.”
• “During the surgery, both appendixes were inflamed.”
• “I read that some people are born with extra appendixes.”
• “The doctor explained that appendixes can vary in size.”

Common Mistakes

Mistake 1: Using “Appendices” for Body Parts

Incorrect: “The surgeon removed his appendices.”
Correct: “The surgeon removed his appendixes.”
Why: In medical writing, appendixes is the standard plural for the organ. Using appendices here sounds overly academic and may confuse readers.

Mistake 2: Using “Appendixes” for Book Sections

Incorrect: “The appendixes at the end of the book are helpful.”
Correct: “The appendices at the end of the book are helpful.”
Why: In publishing and academia, appendices is the preferred form. Using appendixes can make your writing seem less polished.

Mistake 3: Mixing Both Forms in One Document

Incorrect: “See appendix A and B in the appendices. The appendixes also contain maps.”
Correct: “See appendix A and B in the appendices. The appendices also contain maps.”
Why: Consistency matters. Choose one form and stick with it throughout your document.

Mistake 4: Overcorrecting to “Appendices” Everywhere

Some learners think appendices is always more correct because it sounds formal. But in everyday conversation or medical contexts, it can sound unnatural. For example, saying “I had appendicitis in both appendices” is technically understood but sounds odd to native speakers.

Better Alternatives and When to Use Them

If you are unsure which plural to use, consider these alternatives:

• Supplementary materials – Use this in formal writing when you want to avoid the plural altogether. Example: “The supplementary materials are attached.”
• Addenda – This is another Latin plural, but it refers to additions to a document, not necessarily sections at the end. Use it only if you mean “things added.”
• Back matter – A publishing term for material at the end of a book, including appendices, glossaries, and indexes. Example: “The back matter includes several appendices.”
• Extra sections – A simple, clear phrase for informal contexts. Example: “Check the extra sections at the end.”

When in doubt, match your audience. If you are writing a formal report, use appendices. If you are writing an email to a colleague about a medical issue, use appendixes. For general conversation, either is fine, but appendixes feels more natural.

Mini Practice: Test Your Understanding

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

1. The research paper includes three __________. (appendices / appendixes)
2. During the autopsy, the doctor found two __________. (appendices / appendixes)
3. Please refer to the __________ for the full dataset. (appendices / appendixes)
4. Some people are born with a third __________. (appendix / appendices)

Answers

1. Appendices – Academic context.
2. Appendixes – Medical context.
3. Appendices – Formal document context.
4. Appendix – Singular form is correct here; the sentence refers to one organ.

FAQ: Common Questions About the Plural of Appendix

1. Is “appendices” the only correct plural?

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

2. Can I use “appendix” as a plural?

No. Appendix is singular. Using it as a plural is a common error. For example, “The appendix are missing” is incorrect. Always use appendices or appendixes for more than one.

3. Which plural is used in style guides like APA or Chicago?

Most style guides, including APA and Chicago, recommend appendices for academic and professional writing. However, they accept appendixes as a valid alternative in less formal contexts.

4. Does the meaning change depending on the plural?

No, the meaning is the same. Both refer to multiple appendixes (the organ) or multiple appendices (the document sections). The difference is purely about formality and tradition.

Final Tip for Real Writing

When you are writing an email, a report, or a conversation, ask yourself: Is this formal or informal? If it is formal, choose appendices. If it is informal or medical, choose appendixes. If you are still unsure, appendices is the safer choice for most written work, but appendixes will never be wrong in casual use. Practice with the examples above, and soon the choice will feel natural.

For more help with tricky plurals, explore our Confusing Plurals section. You can also check Common Plural Forms or Plural Spelling Rules for additional guidance. If you have questions, visit our FAQ page or contact us.