Both appendixes and appendices are correct plural forms of appendix. The best choice often depends on the type of writing, the meaning of the noun, and any style guide you are following.
In academic papers, reports, books, and other formal documents, appendices is usually the safest choice. Appendixes is also standard English, however, and it appears in general writing as well as discussions of anatomy.
The difference is therefore not a simple matter of one correct form and one error. It is a case of two accepted plurals with different usage tendencies.
Quick Answer
Both forms are grammatically correct:
- Use appendices as the conventional choice for supplementary sections in papers, reports, books, and professional documents.
- Use appendixes when it sounds more natural in general English, especially when discussing anatomical structures.
- Follow the required style guide and use one form consistently throughout the same document.
What Is Correct?
Appendixes and appendices are both correct.
The singular noun is appendix:
“The report includes one appendix.”
When referring to two or more, you may write:
“The report includes three appendices.”
“The report includes three appendixes.”
Neither plural is automatically ungrammatical. However, many readers expect appendices in formal documents. Some editorial styles also require it.
For that reason, appendices is usually the better default for academic, technical, legal, and professional writing.
The Core Grammar Rule
The noun appendix has two accepted plural patterns.
The regular English pattern keeps the complete singular form and adds -es:
appendix → appendixes
The traditional Latin-based pattern changes the ending:
appendix → appendices
English contains many words borrowed from other languages. Some develop a regular English plural while keeping an older plural as an accepted alternative. Appendix belongs to this group.
This means the choice is not controlled by subject-verb agreement, possession, or sentence position. Both words function as plural count nouns.
Correct:
“The appendices contain supporting charts.”
“The appendixes contain supporting charts.”
Because both subjects are plural, both take the plural verb contain.
When Each Form Is Correct
The following table gives practical guidance rather than an absolute division.
| Form or Pattern | Best Use | Why |
|---|---|---|
| Appendices | Academic papers, reports, books, manuals, and formal documents | It is the established conventional form in many publishing and professional settings |
| Appendixes | General English and some anatomical contexts | It follows the regular English plural pattern and is fully accepted |
| Either form | Writing with no required style guide | Both are standard when used clearly and consistently |
Use appendices when a teacher, editor, publisher, employer, or style manual expects it.
Use appendixes when it fits the language of your field or sounds more natural in the sentence.
In medical or anatomical discussion, appendixes may help readers immediately think of more than one bodily structure. Still, appendices can also be used in anatomical writing.
When It Is Incorrect or Less Natural
Neither accepted plural is inherently incorrect. Problems arise mainly from context, consistency, or sentence structure.
Using appendixes may feel less natural in a formal research paper because many academic readers expect appendices. That does not make the word grammatically wrong. It makes it less conventional for that setting.
Switching between the two forms without a reason can also look careless:
“The appendices contain survey questions. Two of the appendixes include charts.”
A consistent version is smoother:
“The appendices contain survey questions. Two of the appendices include charts.”
Forms such as appendixs, appendix’s as a plural, and appendice as the singular are incorrect in standard English.
Meaning, Structure, or Emphasis Differences
The two plurals normally have the same basic meaning: more than one appendix.
They do not create a dependable meaning difference by themselves. Some writers prefer appendices for sections added to documents and appendixes for anatomical structures, but this is a usage tendency rather than a universal grammatical rule.
Compare:
“The thesis has four appendices.”
“The medical text compares the appendixes of several mammals.”
These sentences follow a familiar distinction, but the other plural would still be possible in each sentence.
The clearest difference is often one of convention. Appendices can sound more formal or academic. Appendixes follows a more recognizable English plural pattern and may sound more direct in ordinary speech.
Real-World Examples
The professor asked us to move the raw survey responses to the appendices.
The annual report contains appendices with financial data and policy details.
Please review Appendices A and B before tomorrow’s meeting.
The textbook includes two appendixes with additional practice exercises.
The surgeon discussed differences among the patients’ appendixes.
Researchers examined the appendices of several animal species.
Our department requires all appendices to appear after the reference list.
The editor changed every instance of appendixes to appendices to match the publisher’s style.
Each example uses a plural form correctly. The surrounding context simply makes one form more expected than the other.
Common Mistakes (and Quick Fixes)
A common mistake is treating appendices as singular.
Incorrect: “The report has one appendices.”
Correct: “The report has one appendix.”
Another mistake is adding an apostrophe to create the plural.
Incorrect: “The report contains three appendix’s.”
Correct: “The report contains three appendixes.”
Correct: “The report contains three appendices.”
Writers may also assume that appendixes is always wrong because it sounds less formal. It is an established English plural, though a particular style guide may prefer another form.
Finally, avoid using the plural label for one section. Write Appendix A, not Appendices A. The word becomes plural only when referring collectively to multiple sections.
Grammar Rule Details
Rule
The singular form is appendix. Its two accepted plurals are appendixes and appendices.
Use a plural verb when either plural is the subject:
“The appendices are complete.”
“The appendixes are complete.”
Correct Usage
Use appendices for multiple supplemental sections when following common academic or professional conventions.
Use appendixes when your chosen editorial style permits it or when it is natural in anatomical or general discussion.
Maintain the same form throughout one document unless quoted material requires otherwise.
Incorrect or Less Natural Usage
Appendixs is not a standard plural.
Appendix’s is possessive, not plural:
“The appendix’s title was unclear.”
In a formal research paper, appendixes may be less conventional even though it is grammatically accepted.
Examples
“The proposal has one appendix.”
“The final report has five appendices.”
“The reference book includes several appendixes.”
“The appendices were submitted separately.”
“The doctors compared the two appendixes.”
Common Mistakes
Keep singular and plural forms clearly separated. Avoid adding an apostrophe simply because the word ends in x. Remember that both accepted plural forms can be correct depending on the context. Check whether your school, publisher, or workplace has a preferred form.
Exceptions
There are no major grammatical exceptions to the two accepted plurals.
The main restriction comes from house style. An organization may require appendices, even though general dictionaries accept both forms.
Quick Test
Ask two questions:
Are you referring to one? Use appendix.
Are you referring to more than one? Use appendices or appendixes. Choose appendices when formal convention or a style guide matters.
Usage Notes
The pronunciation changes with the plural.
Appendixes is commonly pronounced “uh-PEN-dik-siz.”
Appendices is commonly pronounced “uh-PEN-duh-seez.”
The pronunciation difference does not change the basic meaning.
FAQ
Are appendixes and appendices both correct?
Yes. Both are accepted plural forms of appendix. Their use differs mainly by convention, context, and editorial preference.
Which form is better for academic writing?
Use appendices unless your institution or required style guide says otherwise. It is the conventional form in research papers, theses, reports, and many professional documents.
Should I use appendixes for body parts?
You may. Some dictionaries describe appendixes as the usual anatomical plural. However, appendices also appears in medical and scientific writing, so the distinction is not absolute.
Is appendixes informal English?
Not necessarily. It is a standard plural formed through the regular English -es pattern. It may simply be less conventional than appendices in formal document structure.
What is the singular of appendices?
The singular form is appendix.
Correct: “Read the appendix.”
Correct: “Read the appendices.”
Should multiple sections be called Appendix A and Appendix B?
Yes. Each individual section is labeled with the singular word: Appendix A, Appendix B, and Appendix C. Collectively, they are the appendices or appendixes.
Conclusion
Both appendixes and appendices are grammatically correct plurals of appendix.
For academic papers, reports, books, and professional documents, appendices is usually the safest and most familiar choice. Appendixes remains a valid standard form and is particularly common in some anatomical contexts.
The best rule is practical: follow the required style, choose the form your readers will expect, and remain consistent throughout your document.
