The plural of diagnosis is diagnoses. It is spelled by changing the ending -is to -es, and it is pronounced die-ag-NOH-seez or, in IPA, /ˌdaɪ.əɡˈnoʊ.siːz/. Use diagnosis for one identified condition or assessment and diagnoses for two or more.
Key Facts at a Glance
- Diagnosis is the singular noun for one identified condition, explanation, or assessment.
- Diagnoses is the plural noun for two or more conditions, explanations, or assessments.
- Diagnoses is pronounced with a final “eez” sound, /ˌdaɪ.əɡˈnoʊ.siːz/.
- The spelling changes from diagnosis to diagnoses, not diagnosises.
- The singular possessive is diagnosis’s; the plural possessive is diagnoses’.
- Diagnosis can describe medical, technical, mechanical, or general problem identification.
What Is the Plural of Diagnosis?
The plural of diagnosis is diagnoses. The word follows a traditional Greek-derived pattern in which a noun ending in -is changes to -es in the plural, as in analysis/analyses and crisis/crises.
A single identified condition is a diagnosis: “The physician made a diagnosis.” More than one identified condition is represented by diagnoses: “The physicians compared three diagnoses.” The same distinction applies outside medicine, such as “The technician recorded two possible diagnoses for the engine fault.”
| Number | Correct form | Example | Meaning |
|---|---|---|---|
| Singular | diagnosis | One diagnosis was recorded. | One condition or explanation |
| Plural | diagnoses | Several diagnoses were considered. | Two or more conditions or explanations |
| Singular possessive | diagnosis’s | The diagnosis’s wording was revised. | Belonging to one diagnosis |
| Plural possessive | diagnoses’ | The diagnoses’ codes differed. | Belonging to multiple diagnoses |
The plural does not mean “a more detailed diagnosis.” It indicates quantity. A clinician can make one complex diagnosis, while a patient can receive several separate diagnoses.
How Do You Spell Diagnoses?
Diagnoses is spelled d-i-a-g-n-o-s-e-s. To form it from diagnosis, remove the final -is and add -es:
diagnosis → diagnoses
The transformation is not created by simply appending -es to the singular. Writing diagnosises incorrectly preserves the singular ending and adds a second plural ending. English uses the established plural form diagnoses instead.
| Singular ending | Correct plural | Incorrect form | Example |
|---|---|---|---|
| -is | diagnoses | diagnosises | diagnosis, diagnoses |
| -is | analyses | analysises | analysis, analyses |
| -is | crises | crisises | crisis, crises |
| -is | theses | thesises | thesis, theses |
| -is | bases | basises | basis, bases |
| -is | hypotheses | hypothesises | hypothesis, hypotheses |
The spelling can be difficult because the letters do not reveal the pronunciation immediately. In diagnoses, the first s belongs to the stem, while the final -es produces the ending sound.
A Reliable Spelling Test
Replace the word with one diagnosis or several diagnoses. If the sentence refers to multiple conditions or explanations, choose diagnoses.
- “The report lists one diagnosis.”
- “The report lists four diagnoses.”
- “The team rejected the initial diagnosis.”
- “The team rejected the initial two diagnoses.”
This substitution test works in medical records, research writing, insurance documents, engineering reports, and ordinary conversation.
How Is Diagnoses Pronounced?
Diagnoses is pronounced die-ag-NOH-seez, with a final eez sound. The singular diagnosis ends in a “sis” sound, while the plural diagnoses ends in a long “ease” sound.
| Word | Pronunciation guide | IPA | Final sound |
|---|---|---|---|
| diagnosis | die-ag-NOH-sis | /ˌdaɪ.əɡˈnoʊ.sɪs/ | “sis” |
| diagnoses | die-ag-NOH-seez | /ˌdaɪ.əɡˈnoʊ.siːz/ | “seez” |
| analysis | uh-NAL-uh-sis | /əˈnæləsɪs/ | “sis” |
| analyses | uh-NAL-uh-seez | /əˈnæləsiːz/ | “seez” |
The stress remains on the NOH syllable in both forms. The plural changes the final vowel and consonant pattern, but it does not move the main stress to the ending.
A frequent spoken error is pronouncing diagnoses exactly like diagnosis. The written difference is small, but the final sound clearly distinguishes singular from plural in speech.
Is Diagnoses Singular or Plural?
Diagnoses is plural. A plural verb usually follows it when diagnoses functions as the subject: “The diagnoses were recorded in the patient’s chart.”
The singular noun diagnosis takes a singular verb: “The diagnosis was recorded.” The difference matters because the verb confirms whether the writer means one assessment or multiple assessments.
| Subject | Correct verb | Example |
|---|---|---|
| One diagnosis | was | The diagnosis was confirmed. |
| Several diagnoses | were | The diagnoses were confirmed. |
| One diagnosis | explains | The diagnosis explains the symptoms. |
| Several diagnoses | explain | The diagnoses explain the symptoms. |
| One diagnosis | requires | The diagnosis requires further testing. |
| Several diagnoses | require | The diagnoses require further testing. |
A sentence can contain diagnoses as an object rather than a subject:
- “The specialist considered several diagnoses.”
- “The software generated possible diagnoses.”
- “The report compared competing diagnoses.”
In those examples, the subject and verb agree with specialist, software, and report, not with diagnoses.
What Is the Difference Between Diagnosis and Diagnoses?
Diagnosis refers to one identified condition or explanation, whereas diagnoses refers to two or more. The distinction is grammatical, not a distinction between medical certainty levels.
“Her diagnosis is asthma” identifies one condition. “Her diagnoses are asthma and eczema” identifies two conditions. A differential diagnosis can also contain several possible explanations, even when only one final diagnosis will eventually be confirmed.
| Situation | Singular or plural | Correct example |
|---|---|---|
| One confirmed condition | Singular | The diagnosis was pneumonia. |
| Two confirmed conditions | Plural | The diagnoses were pneumonia and influenza. |
| One possible explanation | Singular | The leading diagnosis was infection. |
| Several possible explanations | Plural | The differential included five diagnoses. |
| One machine fault | Singular | The diagnosis was a failed sensor. |
| Several system faults | Plural | The diagnoses included network and hardware failures. |
The noun can describe a conclusion, a classification, or a professional assessment. It does not always mean that laboratory testing produced absolute certainty.
Why Does Diagnosis Become Diagnoses?
Diagnosis becomes diagnoses because English retained a Greek-derived plural pattern for many nouns ending in -is. The historical pattern usually replaces -is with -es, producing forms such as diagnoses, analyses, and hypotheses.
The Greek noun diagnōsis entered English through Latin and French usage. English has preserved several learned plurals rather than applying the most common native pattern, which would produce a form like “diagnosises.” The standard modern form remains diagnoses in both American and British English.
Which Words Follow the Same Pattern?
Many academic, scientific, and medical terms ending in -is use an -es plural. Their spelling patterns are related, but their pronunciation can vary enough that each word should be checked when formal accuracy matters.
| Singular | Plural | Field or meaning |
|---|---|---|
| analysis | analyses | Detailed examination |
| basis | bases | Foundation or underlying principle |
| crisis | crises | Emergency or turning point |
| hypothesis | hypotheses | Proposed explanation |
| neurosis | neuroses | Psychological condition |
| prognosis | prognoses | Expected outcome |
| synthesis | syntheses | Combination of elements |
| thesis | theses | Extended academic argument |
The pattern is not universal for every English word ending in -is. Some words have anglicized plurals, competing forms, or specialized usage. For example, iris can be pluralized as irises, while axis commonly becomes axes in mathematics and geometry.
How Do You Use Diagnoses in a Sentence?
Use diagnoses when a sentence refers to multiple medical conditions, possible explanations, or technical findings. The word can appear as a subject, direct object, object of a preposition, or modifier in a compound expression.
Examples from different contexts show that the grammatical rule is not limited to doctors or hospitals:
- Medical record: “The patient received diagnoses of migraine and anemia.”
- Differential assessment: “The physician considered several diagnoses before ordering imaging.”
- Research: “The study compared diagnostic criteria across psychiatric diagnoses.”
- Automotive repair: “The scanner produced two possible diagnoses for the warning light.”
- Information technology: “The incident report listed separate diagnoses for the database and network failures.”
- Education: “The counselor reviewed the students’ documented diagnoses.”
The word can refer to confirmed conditions or provisional possibilities. The surrounding verb and adjective often provide the status: confirmed diagnoses, possible diagnoses, competing diagnoses, and incorrect diagnoses all remain grammatically plural.
When Is a Diagnosis Not the Right Word?
Use a more specific noun when the writer means something other than a formal identification. Symptom describes an observed effect, test result describes measured data, assessment can describe a broader professional judgment, and finding describes an observation.
| Intended meaning | Better term | Example |
|---|---|---|
| One identified condition | diagnosis | The diagnosis was confirmed. |
| Multiple identified conditions | diagnoses | The diagnoses were documented. |
| Observed effect | symptom | Fatigue was the main symptom. |
| Measured laboratory outcome | test result | The test result was positive. |
| General professional judgment | assessment | The assessment covered mobility and pain. |
| Observed abnormality | finding | The scan showed an incidental finding. |
Calling every observation a diagnosis can overstate certainty. A scan may reveal a finding, while a physician’s interpretation may lead to a diagnosis after considering history, examination, and other evidence.
What Is the Possessive Form of Diagnosis?
The singular possessive is usually diagnosis’s, while the plural possessive is diagnoses’. Use diagnosis’s for something belonging to one diagnosis and diagnoses’ for something belonging to multiple diagnoses.
- “The diagnosis’s wording was updated.”
- “The diagnoses’ codes appeared in separate sections.”
- “The physician explained the diagnosis’s implications.”
- “The researchers compared the diagnoses’ accuracy.”
| Number | Possessive form | Example |
|---|---|---|
| One diagnosis | diagnosis’s | The diagnosis’s criteria were reviewed. |
| More than one diagnosis | diagnoses’ | The diagnoses’ criteria differed. |
| One diagnosis, alternative style | diagnosis’ | The diagnosis’ criteria were reviewed. |
| More than one diagnosis | diagnoses’ | The diagnoses’ criteria differed. |
Most current style guidance accepts diagnosis’s for the singular possessive because the word is pronounced with an additional syllable in the possessive form. Some editorial systems allow diagnosis’, especially in specialized institutional writing. Consistency within one document matters more than switching between systems.
The apostrophe does not create the plural. Diagnoses is already plural without an apostrophe.
Is Diagnosises a Correct Word?
Diagnosises is not the standard plural of diagnosis. The accepted plural is diagnoses, and formal writing should use that form in medical, academic, business, and technical documents.
“Diagnosises” appears occasionally when a writer applies a regular English plural rule without recognizing the inherited form. It may be understandable, but dictionaries and professional usage do not treat it as the standard plural.
| Intended meaning | Standard form | Avoid |
|---|---|---|
| One condition | diagnosis | diagnosi |
| Multiple conditions | diagnoses | diagnosises |
| One condition’s property | diagnosis’s | diagnosies |
| Multiple conditions’ property | diagnoses’ | diagnoses’s |
The error is especially easy to make when speaking, because a writer may hear the final sound and try to represent it as -sises. Memorizing the transformation diagnosis → diagnoses prevents both spelling and editing mistakes.
Does the Plural Change in Medical Coding?
The grammatical plural remains diagnoses even when medical coding systems assign separate codes. A record can contain multiple diagnoses, and each diagnosis may have its own ICD-10-CM code or other classification identifier.
Coding systems do not change the noun’s spelling. A hospital document might state that a patient has three diagnoses, then list three codes. The code identifies a classification category, while diagnoses identifies the number of documented conditions or assessments.
The term principal diagnosis has a specialized administrative meaning in hospital reporting. Secondary diagnoses describe additional conditions that affect care, treatment, monitoring, or length of stay. Both expressions use the same ordinary singular and plural grammar.
The word also appears in psychiatric, neurological, genetic, and chronic-care contexts. Multiple diagnoses may describe comorbid conditions, but a list of possible diagnoses is not automatically a list of confirmed conditions. Writers should distinguish possible diagnoses, working diagnoses, and confirmed diagnoses when accuracy affects patient understanding or clinical communication.
Can Diagnoses Be Used Outside Medicine?
Diagnoses can describe formal problem identification outside medicine. Engineers, mechanics, software specialists, and researchers use the term when they identify the cause or category of a fault, failure, or observed phenomenon.
Examples include:
- “The diagnostic system produced three diagnoses for the transmission fault.”
- “The engineers compared competing diagnoses of the structural failure.”
- “The application’s built-in diagnostics suggested two diagnoses.”
- “The report evaluated competing diagnoses for the unusual chemical reaction.”
In everyday nonmedical writing, explanations, causes, findings, or assessments may sound more natural. Diagnoses implies a structured conclusion based on evidence, so it is strongest when a trained person or formal system has classified a problem.
What Is the Difference Between a Technical Diagnosis and a Medical Diagnosis?
A medical diagnosis identifies a disease, disorder, injury, or other health condition. A technical diagnosis identifies a fault, failure mode, or system condition. Both uses preserve the same plural, diagnoses, because the grammatical number does not depend on the field.
| Context | Singular example | Plural example |
|---|---|---|
| Medicine | The diagnosis was diabetes. | The diagnoses included diabetes and hypertension. |
| Automotive | The diagnosis was a worn sensor. | The diagnoses included sensor and wiring faults. |
| Software | The diagnosis was a memory leak. | The diagnoses included memory and database errors. |
| Research | The diagnosis was a processing bias. | The diagnoses reflected several mechanisms. |
The technical use is legitimate, but it can sound metaphorical in informal prose. Choose root causes or faults when the document does not involve a formal diagnostic assessment.
What Common Errors Involve Diagnosis?
The most common errors are diagnosises, confusion between diagnosis and diagnoses, incorrect verb agreement, and misplaced apostrophes. These mistakes arise because the plural is irregular in ordinary English spelling and because the singular and plural sound similar until the final syllable.
Error 1: Writing Diagnosises
Incorrect: “The report contained two diagnosises.”
Correct: “The report contained two diagnoses.”
Error 2: Using a Singular Verb
Incorrect: “The diagnoses was unclear.”
Correct: “The diagnoses were unclear.”
Error 3: Using the Plural for One Case
Incorrect: “The patient’s diagnoses was confirmed.”
Correct: “The patient’s diagnosis was confirmed.”
Error 4: Adding an Apostrophe to Make a Plural
Incorrect: “The diagnosis’s were reviewed.”
Correct: “The diagnoses were reviewed.”
An apostrophe indicates possession or contraction in this context. It does not normally create a plural noun.
Expert Usage Rules
- Count the conditions, not the tests. Five tests can contribute to one diagnosis.
- Separate possibilities from conclusions. A differential contains possible diagnoses, while a final report may document one confirmed diagnosis.
- Check the verb. “Diagnoses were” signals plural; “diagnosis was” signals singular.
- Avoid overstating evidence. A test finding is not always a diagnosis.
- Read the final syllable aloud. “Diagnosis” ends in “sis”; “diagnoses” ends in “seez.”
These rules prevent errors that spell-checkers may miss, because diagnosis, diagnoses, and diagnosis’s are all valid words in different grammatical situations.
Frequently Asked Questions
Is the Plural of Diagnosis Diagnoses or Diagnosises?
The correct plural is diagnoses. Diagnosises is a nonstandard formation and should be avoided in formal writing. The spelling changes from diagnosis to diagnoses by replacing the final -is with -es.
Are Diagnosis and Diagnoses Pronounced Differently?
Yes. Diagnosis is pronounced approximately “die-ag-NOH-sis,” while diagnoses is pronounced “die-ag-NOH-seez.” The plural ends with a long “eez” sound, which distinguishes it from the singular in careful speech.
Is the Plural of Prognosis Also Prognoses?
Yes. The plural of prognosis is prognoses, pronounced approximately “prog-NOH-seez.” Prognosis means an expected outcome, while diagnosis means an identified condition or explanation.
What Is the Plural of Differential Diagnosis?
The plural is differential diagnoses. Differential functions as an adjective, and diagnoses carries the plural marking. For example, “The clinicians considered several differential diagnoses.”
What Is the Verb Related to Diagnosis?
The verb is diagnose. Its forms include diagnoses for third-person singular present tense, diagnosed for past tense, and diagnosing for the present participle. For example, “The specialist diagnoses the condition,” but “The specialist documented two diagnoses.”
Should I Write Diagnoses or Diagnoses’?
Write diagnoses when the noun is plural without possession: “The diagnoses were recorded.” Write diagnoses’ when something belongs to multiple diagnoses: “The diagnoses’ criteria differed.” The apostrophe follows the final s because diagnoses is already plural.
The Bottom Line
The plural of diagnosis is diagnoses, never diagnosises. Use diagnosis for one condition, explanation, or formal assessment, and use diagnoses for two or more. The plural is pronounced “die-ag-NOH-seez,” follows a Greek-derived -is to -es pattern, and applies in medical and technical writing alike. When checking your sentence, count the identified conditions, confirm subject-verb agreement, and reserve apostrophes for possession rather than ordinary plural formation.
