Quick answer: Use appendix when referring to a single supplementary section at the end of a report. Use appendices when referring to two or more supplementary sections. “Appendixes” is an acceptable alternative plural in some medical or general contexts, but “appendices” remains the standard and preferred plural in academic, business, and formal report writing.
When drafting a formal document, the choice between “appendix” and “appendices” frequently trips up even seasoned writers. The confusion stems from the word’s Latin origins, which dictate an irregular plural form that defies standard English rules. As a veteran copy editor who has corrected this exact mistake in countless manuscripts, cover letters, and corporate reports, I can tell you that getting this right instantly elevates your professional credibility.
This guide provides the single clearest, fastest answer to ensure you never second-guess this spelling again. We will break down the exact rules, provide realistic examples of common errors and their fixes, and give you a foolproof memory trick to lock this knowledge in permanently.
| Term | Meaning / When to use | Example sentence |
|---|---|---|
| Appendix | Singular noun. Use when referring to exactly one supplementary section attached to the end of a document. | Please review the financial data located in the appendix of the quarterly report. |
| Appendices | Plural noun. Use when referring to two or more supplementary sections attached to the end of a document. | The research methodology and raw survey data are detailed in the appendices. |
When to use appendix
You should use the singular form “appendix” whenever your report contains only one supplementary section at the end. This section typically holds material that is too detailed, bulky, or tangential for the main body of the text but is still necessary for completeness.
According to the Purdue OWL guide on footnotes and appendices, an appendix can contain figures, tables, raw data, or detailed descriptions that would otherwise interrupt the flow of your main argument. If you only have one of these collections, it is a single appendix.
Here are realistic examples of how to use “appendix” correctly, along with common errors I frequently correct in professional editing:
- Email to a client:
- Incorrect: I have attached the revised proposal; please see the appendixes for the updated timeline.
- Correct: I have attached the revised proposal; please see the appendix for the updated timeline.
- Resume or Cover Letter:
- Incorrect: My portfolio includes a detailed case study, which are available in the appendices.
- Correct: My portfolio includes a detailed case study, which is available in the appendix.
- Internal team text message:
- Incorrect: Hey, the budget breakdown is in the appendices. (When referring to a single section).
- Correct: Hey, the budget breakdown is in the appendix.
The rule is absolute: one supplementary section equals one appendix. Do not let the presence of multiple charts, tables, or pages within that single section trick you into using the plural. The section itself is the singular unit.
When to use appendices
You must use the plural form “appendices” when your document contains two or more distinct supplementary sections. In formal report writing, these are typically labeled sequentially, such as Appendix A, Appendix B, and Appendix C. Collectively, these multiple sections are referred to as the appendices.
The Rasmussen University APA Style guide on appendices emphasizes that if you have multiple appendices, each should start on a new page and be clearly labeled with a letter or number. When referring to them as a group in your main text, “appendices” is the grammatically correct and professionally expected term.
Here are realistic examples demonstrating the correct use of “appendices,” contrasted with errors I routinely fix in corporate and academic drafts:
- Formal business report:
- Incorrect: The technical specifications and the user interview transcripts are located in the appendix.
- Correct: The technical specifications and the user interview transcripts are located in the appendices.
- Academic thesis submission email:
- Incorrect: I have submitted my thesis, including the appendix containing the survey and the appendix containing the raw data.
- Correct: I have submitted my thesis, including the appendices containing the survey and the raw data.
- Project management update:
- Incorrect: Refer to the appendixes for the Q1 and Q2 performance metrics.
- Correct: Refer to the appendices for the Q1 and Q2 performance metrics.
Notice that in the last example, “appendixes” was replaced. While “appendixes” is a recognized plural in some dictionaries, it is widely considered less formal and is primarily reserved for medical contexts (referring to the anatomical organ). In report writing, “appendices” is the undisputed standard. Commit to “appendices” for all professional documents to maintain a polished, authoritative tone.
How to remember the difference
The most reliable way to remember the difference is to link the word to its Latin root and use a simple visual mnemonic.
The word “appendix” comes from the Latin appendere, meaning “to hang upon.” In Latin, nouns ending in “-ix” typically form their plural by changing the “-ix” to “-ices.” Think of other common Latin-derived words that follow this exact same pattern:
- Matrix becomes matrices.
- Index becomes indices.
- Appendix becomes appendices.
The Editor’s Memory Trick: Think of the “I” in “appendix” as standing for “Individual” or “1“. If you have only one section, it is an appendix. Think of the “I-C-E” in “appendices” as standing for “Include Content Extras” (plural). If you have multiple sections, you are including multiple extras, so you need the “ice” ending: appendices.
Alternatively, remember the phrase: “One appendix, multiple appendices.” The shift from ‘x’ to ‘ces’ is the same linguistic shift you see in “index” to “indices.” If you would write “indices” for multiple indexes, you must write “appendices” for multiple appendixes. This parallel is the most powerful tool a writer can use to avoid this specific spelling error.
Common mistakes and exceptions
Even with a clear rule, writers frequently stumble into a few specific traps. As an editor, I see these mistakes constantly in cover letters, annual reports, and student papers. Understanding these edge cases will bulletproof your writing.
Mistake 1: Pluralizing based on the contents of the section. Writers often see multiple graphs, tables, or pages within a single supplementary section and incorrectly use the plural “appendices.”
- The Error: “The appendices contain five different charts.” (Assuming it is one section labeled “Appendix A”).
- The Fix: “The appendix contains five different charts.” The section is singular, regardless of how many items are inside it.
Mistake 2: Using “appendixes” in formal business or academic writing. While Merriam-Webster lists “appendixes” as a valid plural, its usage is heavily skewed toward anatomy (e.g., “The surgeon removed two infected appendixes”). In the context of reports, academic papers, and business documentation, “appendices” is the overwhelmingly preferred and expected plural. Using “appendixes” in a formal report signals to a discerning reader or editor that you may not be familiar with standard academic conventions.
Mistake 3: Inconsistent labeling in the table of contents. A frequent structural error is labeling individual sections as “Appendices A” and “Appendices B.”
- The Error: “See Appendices A for the budget and Appendices B for the timeline.”
- The Fix: “See Appendix A for the budget and Appendix B for the timeline. Both are located in the appendices at the end of the report.” The plural “appendices” is only used when referring to the group as a whole, never when identifying a single, specific section by its letter or number.
US vs. UK Differences: Fortunately, this is one area where US and UK English are in complete agreement. Both American and British style guides (including APA, Chicago, and Oxford) mandate “appendix” for the singular and “appendices” for the plural in formal writing. You do not need to adjust this spelling based on your target audience’s geography.
Frequently Asked Questions
Is “appendixes” ever correct in a report? Technically, yes, as it is a recognized English plural, but it is strongly discouraged in formal, academic, or business report writing. Always default to “appendices” to ensure your document maintains a professional and authoritative tone.
How do I refer to a specific appendix when there are multiple? When pointing to a single, specific section within a group of supplementary materials, always use the singular “appendix” followed by its designated letter or number. For example, write “Refer to Appendix B for the survey questions,” not “Refer to Appendices B.”
What is the difference between an appendix and an attachment? An appendix is integrated into the main document and paginated as part of it, providing supplementary context for the reader. An attachment is a separate, standalone file (like a separate PDF or spreadsheet) sent alongside the main document, often referenced but not physically bound within the same page count.
Do I need a table of contents entry for my appendices? Yes. If your report includes an appendix or appendices, you should list them in your main table of contents. If you have multiple, list them individually (e.g., “Appendix A: Survey Data ……. 15”) so readers can easily locate the specific supplementary material they need.
Steven Garcia has dedicated over a decade to exploring the intricacies of the English language, specializing in word comparisons and nuanced linguistic distinctions. Holding a master’s degree in Linguistics from the University of California, Steven has always been fascinated by the dynamic evolution of language. He began his career as an editor for several publishing houses, where he honed his skills in discerning subtle differences in word usage. Steven is particularly interested in the etymology and historical contexts that shape word meanings. His passion for language led him to join WhichWordHub, where he focuses on creating insightful content that helps readers understand the subtle differences between similar words. Through his work, Steven aims to enrich the vocabulary of language enthusiasts and empower them to make informed word choices. In addition to writing detailed articles, he enjoys engaging with the linguistic community to discuss the ever-evolving nature of English.