Appendix Plural Form: Rule, Examples, and Mistakes
If you are writing a business report, an academic paper, or an email and need to refer to more than one appendix, the correct plural form is appendices (pronounced uh-PEN-duh-seez) in formal and academic contexts, and appendixes (pronounced uh-PEN-dik-siz) in general and technical writing. Both forms are accepted in modern English, but the choice depends on your audience and the tone of your document. This guide explains the rule, gives you practical examples, highlights common mistakes, and helps you choose the right form for your writing.
Quick Answer: Appendix Plural
- Appendices – Preferred in academic, legal, and formal business writing. This follows the original Latin plural pattern.
- Appendixes – Common in technical manuals, software documentation, and everyday business communication. This follows the standard English plural rule (add -es).
- Both are correct. Use appendices for a formal or scholarly tone. Use appendixes for a straightforward, modern tone.
Why Two Plural Forms?
The word appendix comes from Latin, where nouns ending in -ix often change to -ices in the plural (like index → indices, matrix → matrices). English has kept this Latin plural for formal use. However, English speakers also naturally apply the regular -es ending to many Latin words over time, creating the form appendixes. Both are now standard, but they carry different stylistic weights.
Comparison Table: Appendices vs. Appendixes
| Feature | Appendices | Appendixes |
|---|---|---|
| Origin | Latin plural | English regular plural |
| Tone | Formal, academic, legal | Neutral, technical, conversational |
| Common in | Research papers, books, contracts | User manuals, software, emails, internal docs |
| Example sentence | Please refer to appendices A and B for the full data. | The appendixes contain the installation steps. |
| Reader expectation | Scholarly or traditional audience | General business or technical audience |
Formal vs. Informal: When to Use Each
Formal Contexts (Use appendices)
In academic writing, legal documents, and formal business reports, appendices is the standard choice. It signals that you are following traditional conventions. For example, if you are writing a thesis, a white paper, or a contract, use appendices.
Example in an email to a client:
“We have attached the financial projections in the appendices to the proposal. Please review Appendix I and Appendix II.”
Informal and Technical Contexts (Use appendixes)
In internal company memos, software documentation, or everyday emails, appendixes sounds natural and less stiff. It is also the preferred form in many style guides for technical writing because it is simpler and more direct.
Example in a team chat:
“The appendixes in the user guide have the troubleshooting steps. Check them before calling support.”
Natural Examples in Business Writing
Here are real-world sentences you might write or read in a business setting:
- “The contract includes three appendices that detail the payment schedule.” (formal, legal)
- “Please update the appendixes in the training manual before the next session.” (neutral, internal)
- “All supporting data is located in the appendices at the end of the report.” (formal, academic)
- “The software manual has two appendixes: one for error codes and one for installation.” (technical)
- “We will add the survey results as appendices to the final presentation.” (formal, business)
Common Mistakes with Appendix Plural
Mistake 1: Using appendi or appendicies
Some writers mistakenly drop the -x or add an extra syllable. The correct forms are only appendices and appendixes. Never write “appendi” or “appendicies.”
Wrong: “The appendi are in the back.”
Right: “The appendices are in the back.”
Mistake 2: Mixing singular and plural in the same document
Once you choose a form, stick with it throughout the entire document. Switching between appendix and appendices or appendixes confuses readers.
Wrong: “See appendix A and appendixes B and C.”
Right: “See appendices A, B, and C.”
Mistake 3: Using appendix as a plural
Never use appendix to refer to more than one. It is strictly singular.
Wrong: “The report has several appendix.”
Right: “The report has several appendices.”
Mistake 4: Overusing the Latin plural in casual conversation
Saying “appendices” in a quick email to a colleague can sound overly formal or pretentious. Match the form to the context.
Awkward: “I’ll send you the appendices later today.” (in a casual Slack message)
Better: “I’ll send you the appendixes later today.”
Better Alternatives and When to Use Them
Sometimes you can avoid the plural of appendix altogether by using a clearer word. Consider these alternatives:
- Supplement – Use when the material adds new information, not just supporting data. Example: “The supplement includes updated charts.”
- Addendum – Use for a single addition to a contract or report. Plural: addenda. Example: “Please sign the addendum to the agreement.”
- Attachment – Use in emails for files that are separate from the main message. Example: “See the attachment for the budget breakdown.”
- Annex – Use in formal international documents or standards. Example: “The annex contains the technical specifications.”
When you want to be precise and follow standard business or academic style, stick with appendices or appendixes. Use alternatives when the context calls for a different nuance.
Mini Practice: Test Your Understanding
Choose the correct plural form for each sentence. Answers are below.
- The research paper includes three ______ (appendices / appendixes) with raw data.
- Please check the ______ (appendices / appendixes) in the user manual for the error codes.
- All ______ (appendices / appendixes) must be numbered and listed in the table of contents.
- In our internal documentation, the ______ (appendices / appendixes) are updated quarterly.
Answers:
1. appendices (formal academic context)
2. appendixes (technical manual, neutral tone)
3. appendices (formal report style)
4. appendixes (internal, practical context)
FAQ: Appendix Plural
1. Is it ever wrong to use appendixes?
No. Appendixes is accepted in most dictionaries and style guides. However, in very formal academic or legal writing, some readers may expect appendices. When in doubt, check your organization’s style guide.
2. What is the plural of appendix in a medical context?
In medicine, the plural of appendix (the organ) is almost always appendixes. Doctors and medical writers rarely use appendices for the body part. For example: “Two patients had inflamed appendixes.”
3. How do I pronounce appendices and appendixes?
Appendices is pronounced /əˈpɛndɪsiːz/ (uh-PEN-duh-seez). Appendixes is pronounced /əˈpɛndɪksɪz/ (uh-PEN-dik-siz). The difference is in the last syllable: “seez” vs. “siz.”
4. Can I use appendices in an email to my boss?
Yes, if your workplace culture is formal or if you are writing about a formal document like a proposal or report. If your office communication is casual, appendixes may sound more natural.
Final Tip for Business Writers
When you write a document that includes multiple appendices (or appendixes), be consistent. Choose one form and use it from the first page to the last. If you are writing for a formal audience—such as a client, a board of directors, or an academic journal—use appendices. If you are writing for a general business audience, a technical team, or an internal audience, appendixes is perfectly fine and often clearer. The key is to match your word choice to the tone of your document and the expectations of your reader.
For more help with plural forms in business writing, visit our Plural Spelling Rules section or check our FAQ for common questions. If you have a specific question about a different word, feel free to contact us.
