What Is the Plural of Appendix?

The word appendix has two standard plural forms: appendices and appendixes. Both are correct, but they are used in different contexts. Appendices is the traditional Latin plural and is preferred in academic, medical, and formal writing. Appendixes is the English plural form and is common in general, technical, and everyday use. Your choice depends on your audience and the tone of your writing.

Quick Answer

Use appendices for formal, academic, or medical contexts (e.g., research papers, legal documents, medical reports). Use appendixes for general, technical, or informal writing (e.g., software manuals, business emails, everyday conversation). Both are acceptable, but consistency is key.

Understanding the Two Plurals

The word appendix comes from Latin, where it follows the -ix to -ices plural pattern (like index to indices). Over time, English speakers adopted the regular -es ending, creating appendixes. Today, both forms are widely used, and neither is wrong.

When to Use Appendices

Appendices is the go-to choice in formal writing. You will see it in:

• Academic papers and dissertations
• Medical textbooks and patient reports
• Legal contracts and court documents
• Publishing (book appendices)

Using appendices signals that you are following traditional conventions, which is often expected in these fields.

When to Use Appendixes

Appendixes is the natural English plural. It is common in:

• Technical documentation (software, engineering)
• Business reports and internal memos
• Everyday conversation and informal emails
• General writing where a simpler form is preferred

If you are writing for a general audience or in a less formal setting, appendixes is perfectly fine and often sounds more natural.

Comparison Table: Appendices vs. Appendixes

Natural Examples

Here are examples showing both forms in real contexts:

• Academic: The appendices include the survey questions and participant consent forms.
• Medical: The surgeon noted that the patient’s appendixes were healthy during the procedure.
• Technical: Refer to the appendixes at the end of the user manual for troubleshooting tips.
• Business: We have attached the financial appendices to the quarterly report.
• Conversation: “Did you look at the appendixes in the guide?” “Yes, they had the diagrams I needed.”

Common Mistakes

Even careful writers sometimes make errors with this word. Here are the most frequent ones:

• Using “appendi” or “appendix’s” as a plural: These are incorrect. The plural is never appendi or appendix’s (the latter is the possessive form).
• Mixing forms in the same document: Choose one plural and stick with it throughout your writing. Switching between appendices and appendixes can confuse readers.
• Assuming one is always wrong: Some style guides prefer one over the other, but both are standard. Check your organization’s style guide if you are unsure.
• Overusing the Latin plural in informal writing: Using appendices in a casual email can sound overly formal or pretentious. Match your plural to your audience.

Better Alternatives and When to Use Them

Sometimes you may want to avoid the plural of appendix altogether. Here are alternatives:

• Supplementary materials: Use this in academic or business contexts when referring to extra documents. Example: “The supplementary materials are available online.”
• Addenda: This is a formal term for additional content, often used in contracts or reports. Example: “Please review the addenda before signing.”
• Attachments: Common in emails and business correspondence. Example: “I have included the attachments for your review.”
• Supporting documents: A clear, neutral term for any extra files. Example: “All supporting documents are in the shared folder.”

Use these alternatives when you want to avoid confusion or when the word appendix feels too technical for your audience.

Formal vs. Informal Tone

Your choice of plural also affects the tone of your writing:

• Formal tone: Use appendices in academic papers, legal documents, medical reports, and official publications. It shows attention to traditional conventions.
• Informal tone: Use appendixes in emails, internal memos, blog posts, and everyday conversation. It feels more direct and less stiff.
• Email context: In a professional email to a colleague, appendixes is fine. In a formal proposal to a client, appendices may be more appropriate.
• Conversation nuance: Saying “Check the appendixes” sounds natural. Saying “Check the appendices” might sound like you are reading from a script.

Mini Practice: Test Your Understanding

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

1. The research paper includes three __________ (appendices / appendixes) with raw data.
2. Please review the __________ (appendices / appendixes) in the software manual for setup instructions.
3. The doctor noted that both __________ (appendices / appendixes) were inflamed.
4. We have attached the __________ (appendices / appendixes) to the email for your convenience.

Answers

1. appendices – Academic context calls for the formal plural.
2. appendixes – Technical manual, general audience.
3. appendixes – Medical context, but in a clinical note, either is acceptable; appendixes is common in modern medical writing.
4. appendixes – Informal email, natural English plural.

Frequently Asked Questions (FAQ)

1. Is “appendices” the only correct plural?

No. Both appendices and appendixes are correct. Appendices is the traditional Latin plural, while appendixes is the regular English plural. Your choice depends on context and audience.

2. Can I use “appendix” as a plural?

No. Appendix is singular. The plural forms are appendices or appendixes. Using appendix for more than one is a common error.

3. Which plural should I use in a business report?

It depends on the formality of the report. For a formal report to executives or clients, use appendices. For an internal memo or team document, appendixes is fine. When in doubt, check your company’s style guide.

4. Does the meaning change between “appendices” and “appendixes”?

No. Both refer to the same thing: additional material at the end of a document or the anatomical structure. The difference is only in formality and usage context.

Final Tips for Choosing the Right Plural

To decide between appendices and appendixes, ask yourself three questions:

• Who is my audience? Academics and professionals in formal fields expect appendices. General readers prefer appendixes.
• What is the tone of my writing? Formal writing calls for appendices. Informal or technical writing works well with appendixes.
• What does my style guide say? If you are following a specific guide (APA, MLA, Chicago, or company style), use the form it recommends.

Remember, consistency matters more than which form you choose. Once you pick one, use it throughout your document. For more help with plural forms, visit our Common Plural Forms section or check our FAQ for additional questions. If you have a specific question about your writing, feel free to contact us.