Diagnosis Plural Form: Rule, Examples, and Mistakes
If you are wondering about the plural of diagnosis, the direct answer is diagnoses. This follows the rule for medical and academic words that end in -sis, where the ending changes to -ses in the plural. So one diagnosis, two diagnoses. This guide explains the rule, gives you real examples, points out common mistakes, and helps you use the word correctly in writing, email, and conversation.
Quick Answer: Diagnosis vs. Diagnoses
| Form | Example | Usage |
|---|---|---|
| Singular: diagnosis | The doctor made a clear diagnosis. | Refers to one condition or finding. |
| Plural: diagnoses | The team reviewed three diagnoses. | Refers to more than one condition or finding. |
Remember: diagnosis ends in -sis, so its plural is diagnoses (not diagnosises or diagnosi).
The Spelling Rule for Words Ending in -sis
Many medical and academic terms follow a consistent pattern. Words that end in -sis change to -ses in the plural. This rule applies to words like crisis (crises), thesis (theses), analysis (analyses), and hypothesis (hypotheses). Diagnosis works the same way.
Why does this happen? These words come from Greek, and the plural form in English preserves the original Greek pattern. It is not an irregular plural in the traditional sense—it follows a predictable rule once you know the pattern.
How to Form the Plural Correctly
To make the plural of diagnosis:
- Remove the -sis ending.
- Add -ses.
- Pronunciation changes: diagnosis (dye-ag-NO-sis) becomes diagnoses (dye-ag-NO-seez).
This is the only correct plural form in standard English. There is no alternative accepted plural.
Natural Examples in Context
Seeing the word used naturally helps you remember the form and the tone. Below are examples for different situations.
Formal Writing and Medical Reports
- The patient received two separate diagnoses during the consultation.
- All diagnoses were documented in the electronic health record.
- The study compared diagnoses from three different hospitals.
In formal writing, diagnoses is the standard plural. You will see it in research papers, clinical notes, and official documents. The tone is neutral and professional.
Email and Workplace Communication
- Please send me the diagnoses for the patients we discussed.
- We need to review the differential diagnoses before the meeting.
- Could you clarify the diagnoses listed in the report?
In emails, using the correct plural shows attention to detail. It is especially important in healthcare settings where precision matters.
Everyday Conversation
- The doctor gave me two diagnoses, and I was surprised.
- She had multiple diagnoses over the years.
- I learned about different diagnoses in my class.
In casual conversation, people sometimes say diagnosis when they mean multiple conditions, but careful speakers use diagnoses. Using the correct form makes you sound more educated and precise.
Common Mistakes with the Plural of Diagnosis
Even native speakers make errors with this word. Here are the most frequent mistakes and how to avoid them.
Mistake 1: Using “Diagnosises”
Some people add a regular -es ending, creating diagnosises. This is incorrect because diagnosis does not follow the regular plural rule.
Incorrect: The lab reported three diagnosises.
Correct: The lab reported three diagnoses.
Mistake 2: Using “Diagnosi”
Another error is dropping the -sis and adding -i, as if the word were Latin. Diagnosi is not a word in English.
Incorrect: We compared the diagnosi from both clinics.
Correct: We compared the diagnoses from both clinics.
Mistake 3: Using “Diagnosis” as Both Singular and Plural
Some writers use diagnosis for both one and multiple conditions. This creates confusion, especially in medical contexts where the number matters.
Incorrect: The patient had several diagnosis over the years.
Correct: The patient had several diagnoses over the years.
Mistake 4: Confusing “Diagnosis” with “Prognosis”
While both words follow the same plural rule (prognosis becomes prognoses), people sometimes mix them up. A diagnosis identifies a condition; a prognosis predicts the outcome.
Incorrect: The doctor gave a good diagnosis for recovery.
Correct: The doctor gave a good prognosis for recovery.
Better Alternatives and When to Use Them
Sometimes you may want to rephrase a sentence to avoid the plural form altogether, especially if you are unsure. Here are some alternatives.
| Original (with plural) | Alternative phrasing | When to use |
|---|---|---|
| We reviewed three diagnoses. | We reviewed three cases. | In casual conversation or when the word diagnosis feels too clinical. |
| The diagnoses were accurate. | The findings were accurate. | When you want to focus on results rather than the process. |
| She had multiple diagnoses. | She had several conditions. | In patient-friendly communication. |
| The team discussed the diagnoses. | The team discussed the results. | In general workplace settings. |
Using these alternatives can make your language more accessible, especially when speaking with patients or non-medical colleagues. However, in formal medical writing, stick with diagnoses for accuracy.
Comparison Table: Diagnosis vs. Other -sis Words
| Singular | Plural | Common Error |
|---|---|---|
| diagnosis | diagnoses | diagnosises |
| crisis | crises | crisises |
| thesis | theses | thesises |
| analysis | analyses | analysises |
| hypothesis | hypotheses | hypothesises |
| prognosis | prognoses | prognosises |
This pattern is consistent. Once you learn it for one word, you can apply it to all similar words.
Mini Practice: Test Your Understanding
Try these four questions. Answers are below.
Question 1: Choose the correct sentence.
A. The doctor made two diagnosises.
B. The doctor made two diagnoses.
Question 2: Fill in the blank: The study compared several ______ from different hospitals.
A. diagnosis
B. diagnoses
Question 3: Which word is the correct plural of prognosis?
A. prognosises
B. prognoses
Question 4: True or false: Diagnosis can be used as both singular and plural in formal writing.
Answers:
1. B. The doctor made two diagnoses.
2. B. The study compared several diagnoses from different hospitals.
3. B. Prognoses is the correct plural.
4. False. In formal writing, use diagnosis for singular and diagnoses for plural.
Frequently Asked Questions
1. Is “diagnoses” pronounced differently from “diagnosis”?
Yes. Diagnosis is pronounced dye-ag-NO-sis (with a short i sound at the end). Diagnoses is pronounced dye-ag-NO-seez (with a long eez sound at the end). The change in pronunciation matches the change in spelling.
2. Can I use “diagnosis” as a plural in informal speech?
Some people do in very casual conversation, but it is not correct. If you want to sound clear and professional, use diagnoses for plural. In writing, always use the correct form.
3. What about “differential diagnosis”? Does it have a plural?
Yes. The plural is differential diagnoses. For example: “The team considered three differential diagnoses.” The word differential stays the same; only diagnosis changes.
4. Are there any exceptions to the -sis to -ses rule?
Very few. Most words ending in -sis follow this pattern. One exception is basis, which becomes bases (pronounced BAY-seez). Another is axis, which becomes axes (pronounced AK-seez). The rule is reliable for medical terms like diagnosis.
Final Tip for Learners
The best way to remember the plural of diagnosis is to practice it in context. Write a sentence today using diagnoses. For example: “I read about two different diagnoses in the article.” The more you use it, the more natural it becomes. If you need more help with medical plurals, explore our Plural Spelling Rules section for other patterns. You can also check Common Plural Forms for a broader overview. For specific questions, visit our FAQ page or contact us.
