If you’ve ever stumbled over the word prosthesis and wondered how to make it plural, you’re not alone. The term doesn’t follow the simple “add an s” rule. Instead, it changes in a way that reflects its ancient Greek origins.
The quick answer: the plural of prosthesis is prostheses — not prosthesises and definitely not prostheticals. But there’s more to the story than just memorizing one word form. Understanding why prostheses is correct can help you avoid similar mistakes with other Greek-origin nouns ending in -is.
Let’s break it down, starting with what prosthesis actually means.
What Is a Prosthesis?
The word prosthesis appears most often in two fields — medicine and linguistics.
- In medicine, a prosthesis is an artificial device that replaces a missing body part. This could be:
- A prosthetic leg or arm.
- A dental implant or bridge.
- An artificial heart valve.
- In linguistics, a prosthesis is the addition of a sound or syllable to the beginning of a word. For example:
- Adding an “e” to special to form especial.
- Adding “a” to sleep to form asleep in older English.
Case study – Medical usage:
A 2022 study in the Journal of Prosthetic Dentistry found that more than 3 million people in the U.S. currently live with dental prostheses, a number expected to triple by 2050 due to aging populations.
Case study – Linguistic usage:
In early Latin, the word scribere (“to write”) sometimes appeared as escribere due to prosthesis, a common phonetic shift in Romance languages.
The term is versatile, but its pluralization works the same regardless of the context.
Origins of the Word “Prosthesis”
Prosthesis comes from the Greek word πρόθεσις (prosthesis), meaning “addition” or “application.” It entered English through Latin prosthesis.
The original Greek word combined:
- pros- = “toward” or “in addition.”
- thesis = “placing” or “position.”
Historically, the word described adding something to speech or text. Later, medical science adopted it to describe adding an artificial part to the body.
That Greek origin matters because it determines how we form the plural in English today.
Read More About: Simile vs Metaphor: Definitions, Differences, and Usage
How Words Ending in “-is” Are Pluralized
English borrows many technical and academic words from Greek. A number of these Greek-origin nouns ending in -is become -es in their plural form.
The general medical term pluralization rules for such nouns are:
- Replace the ending -is with -es.
- Keep the root of the word unchanged.
Examples of -is to -es plurals: analysis → analyses, thesis → theses (Grammar Palette).
Other common examples:
- crisis → crises
- basis → bases
- diagnosis → diagnoses
- axis → axes
- oasis → oases
Here’s a quick reference table:
| Singular | Plural | Field | Notes |
|---|---|---|---|
| prosthesis | prostheses | Medical/Linguistics | Correct plural of prosthesis |
| analysis | analyses | Academic/Science | Common in research papers |
| thesis | theses | Academia | Used in academic writing |
| crisis | crises | General | Often in news headlines |
| diagnosis | diagnoses | Medicine | Used in patient records |
Plural of Prosthesis
The plural form of prosthesis is prostheses.
Why? Because it follows the Greek pattern: drop the final -is, replace with -es.
Correct: prosthesis → prostheses
Incorrect: prosthesises (misuse of ‘prosthesis’ in plural form — a common error)
Pronunciation
- Singular: prosthesis → /prɒsˈθiːsɪs/
- Plural: prostheses → /prɒsˈθiːsiːz/
Dictionary Verification
The correct plural in standard dictionaries is listed as prostheses in:
Prosthesis vs Prosthetic
People often confuse prosthesis with prosthetic. They’re related but not identical.
- Prosthesis: noun — the device itself.
Example: “She received a knee prosthesis after her surgery.” - Prosthetic: adjective — describing something related to prostheses.
Example: “He was fitted with a prosthetic leg.”
In casual speech, some people say “prosthetic” as a shortened noun for “prosthetic limb.” But in precise writing, stick to prosthesis for the device and prosthetic for the descriptor.
Examples in Real Sentences
To cement your understanding, here are usage in medical contexts: prostheses and linguistic contexts:
Medical examples:
- “The clinic specializes in designing advanced prostheses for veterans.” (Merriam-Webster)
- “Dental prostheses must be custom-fitted to each patient’s mouth.” (Cambridge Dictionary)
Linguistic examples:
- “In medieval manuscripts, scholars observed multiple cases of prostheses in loanwords from Latin.”
- “The study identified several prostheses used in poetic meter to maintain rhythm.”
Singular vs plural contrast:
- Singular: “The dentist installed a prosthesis.”
- Plural: “The dentist installed three prostheses.”
Synonyms & Related Terms
Medical synonyms:
- Artificial limb
- Implant
- Orthotic device
- Replacement part
Linguistic synonyms:
- Prefix addition
- Initial augmentation
- Sound insertion
These synonyms can be useful for variety, but in technical or academic writing, prosthesis is preferred for accuracy.
Common Mistakes with the Plural of Prosthesis
Here are the errors to avoid:
- Using prosthesises — it’s grammatically incorrect.
- Mixing singular and plural incorrectly:
- Wrong: “These prosthesis are new.”
- Correct: “These prostheses are new.”
- Confusing prosthesis with prothesis — a different term in ecclesiastical contexts.
How to Say Multiple Prosthetic Devices
If “prostheses” feels too formal or technical for your audience, you can rephrase:
- “Multiple prosthetic devices”
- “Several artificial limbs”
- “Various implants”
This is especially helpful in patient-facing materials where plain language improves understanding.
Quick Reference Table
| Form | Spelling | Pronunciation | Example |
|---|---|---|---|
| Singular | prosthesis | /prɒsˈθiːsɪs/ | “The surgeon implanted a dental prosthesis.” |
| Plural | prostheses | /prɒsˈθiːsiːz/ | “The lab manufactures custom prostheses.” |
Final Takeaway
The answer to what is the plural of prosthesis is clear: it’s prostheses.
The pattern comes from Greek, and it’s shared by other technical terms. Mastering it not only keeps your writing correct but also sharpens your grasp of English grammar, especially in specialized fields like medicine and linguistics.
Whether you’re a medical professional, a language scholar, or just someone curious about words, remembering that Greek-origin nouns ending in -is become -es will serve you well. And when in doubt, check a trusted source like Merriam-Webster, Cambridge Dictionary, or Dictionary.com.