When you hear the word thorax, you might picture the chest of a human or the midsection of an insect. But when there are more than one, what do you call them—thoraxes or thoraces? If you’ve seen both, you’re not alone in your confusion. This post explores the correct plural of thorax, why both versions exist, and how to use each one depending on your context.
What Is a Thorax?
The thorax is a term used in biology and anatomy, referring to different things based on the species:
- In humans and mammals, it refers to the chest—the area between the neck and the abdomen. This section houses vital organs like the heart and lungs.
- In insects, the thorax is the middle part of the body. It’s the segment where the legs and wings attach.
This dual use makes the word common in both medical and entomological fields.
Read More About This Article: Word vs Term: What’s the Real Difference and Why It Matters
The Plural of Thorax: Thoraxes vs. Thoraces
Let’s settle the big question: What is the plural of thorax?
Both thoraxes and thoraces are accepted plurals. But they differ in tone, usage, and formality.
Thoraxes (THAW-raks-iz)
- Follows modern English plural rules: just add -es to words ending in -x.
- Seen more in casual writing and everyday contexts.
- Considered intuitive and easy for general audiences.
Thoraces (THAWR-uh-seez)
- Retains its classical Latin form: changing -ax to -aces.
- Preferred in formal, scientific, and academic writing.
- Common in medical texts, journals, and entomology studies.
Here’s a quick comparison:
| Form | Type | Use Case | Example Source |
|---|---|---|---|
| Thoraxes | English Plural | Informal writing, general audience | News articles, textbooks |
| Thoraces | Latin Plural | Formal, scientific, technical usage | Medical journals, academia |
Why Are There Two Plurals?
The dual plurals of thorax come from the tug-of-war between regular English grammar and the preservation of classical Latin structures.
English Pluralization Rule
English nouns ending in -x often add -es to become plural. For example:
- Box → Boxes
- Reflex → Reflexes
- Syntax → Syntaxes
Following this rule, thorax becomes thoraxes.
Latin-Derived Pluralization
Some English words of Latin origin retain their classical plural forms. With thorax, the Latin rule changes -ax to -aces, just like:
- Vertex → Vertices
- Index → Indices
- Appendix → Appendices
Thus, thorax becomes thoraces when following the Latin pattern.
Pronunciation Guide
Getting the plural right isn’t just about spelling—it’s also about saying it correctly.
- Thoraxes: Pronounced /\u02c8\u03b8\u0254\u02d0.r\u00e6ks.\u026az/ → THAW-raks-iz
- Thoraces: Pronounced /\u02c8\u03b8\u0254\u02d0.r\u0259.si\u02d0z/ → THAWR-uh-seez
Using the right pronunciation in professional or academic settings boosts credibility and understanding.
Real Usage in Sentences
Let’s see both singular and plural forms of thorax in context:
- Singular: The doctor placed the stethoscope on the patient’s thorax.
- Thoraxes: Different species have thoraxes that vary in muscle structure.
- Thoraces: Researchers studied the thoraces of over 200 beetle specimens.
These examples show how context and audience dictate which plural form works best.
When to Use Thoraxes or Thoraces
Knowing when to use each form depends on a few factors:
Use thoraxes if:
- You’re writing for a general audience.
- The tone is informal or conversational.
- You’re using other regular English plurals in the same sentence.
Use thoraces if:
- You’re writing for a scientific or medical journal.
- The tone is formal or academic.
- You want to maintain consistency with other Latin-derived terms.
“In anatomy, formality favors thoraces, but clarity often calls for thoraxes.”
Other “-ax” Words and Their Plural Forms
Let’s take a look at how other -ax ending words behave when pluralized.
| Singular | English Plural | Latin Plural | Notes |
|---|---|---|---|
| Thorax | Thoraxes | Thoraces | Both accepted |
| Vertex | Vertexes | Vertices | Latin form used in mathematics |
| Index | Indexes | Indices | Indices for science, indexes for books |
| Matrix | Matrixes | Matrices | Latin form preferred in tech/math |
| Syntax | Syntaxes | — | Only regular plural used |
| Climax | Climaxes | — | Regular plural only |
| Flax | Flaxes | — | Rarely used in plural |
This pattern shows how plural forms often reflect a word’s origin and field of use.
Etymology of Thorax
The word thorax has ancient roots that help explain why its plural forms differ.
- Originates from Ancient Greek thōrāx (θώραξ), meaning “breastplate” or “armor”
- Adopted into Latin as thorax
- Passed into English through medical and scientific texts
The breastplate metaphor makes sense—the thorax protects critical organs just like armor protects the body. Because of its classical roots, many scientific writers retain the Latin plural thoraces.
What Dictionaries and Style Guides Say
Different sources offer their take on the plural of thorax:
- Merriam-Webster: Lists both thoraxes and thoraces as correct.
- Cambridge Dictionary: Accepts both forms, with thoraces marked as formal.
- Oxford English Dictionary: Notes the Latin origin of thoraces, but includes both.
- APA Style Manual: Recommends consistency—choose one form and use it throughout.
Tip: If you’re unsure, stick to thoraxes in everyday writing and thoraces in academic contexts.
Common Mistakes and How to Avoid Them
Here are a few pitfalls writers and speakers often fall into:
- Mixing both plurals in one piece of writing. Choose one and stick with it.
- Incorrect pronunciation, especially in presentations. Practice out loud.
- Assuming one is wrong. Both are correct—but some are more fitting for certain contexts.
Avoid confusion by thinking about your reader or listener first.
Quick Reference: Thorax Plural Cheat Sheet
Use this table when you need a quick reminder:
| Audience Type | Best Plural | Example Use |
|---|---|---|
| General Reader | Thoraxes | “The insect thoraxes were brightly colored.” |
| Medical Professional | Thoraces | “The surgeon examined both thoraces.” |
| Academic Paper | Thoraces | “Data was gathered on insect thoraces.” |
| Classroom Textbook | Thoraxes | “Thoraxes help protect the heart and lungs.” |
Final Thoughts: Thoraxes or Thoraces—What Should You Use?
Now that you’ve seen the difference, the choice is yours. Both thoraxes and thoraces are grammatically correct. The key is choosing the form that fits your audience and purpose.
Whether you’re writing a biology paper, preparing a science presentation, or just trying to use the right word in conversation, knowing the plural of thorax—and when to use it—adds precision to your language.