What does diagnose mean?
To diagnose is to identify the nature of something — most often a disease — by carefully examining its signs, symptoms, and underlying causes. The word is at home in medicine, where doctors diagnose conditions ranging from common infections to rare genetic disorders, but it has extended naturally into everyday analytical language: engineers diagnose engine faults, technicians diagnose software failures, and consultants diagnose problems within organizations. It usually takes the condition as a direct object ('the doctor diagnosed pneumonia') or appears in the passive construction 'diagnosed with', which specifies the person affected. The verb carries a connotation of expertise and systematic investigation, implying that the answer emerges from evidence rather than guesswork. Derived forms such as diagnosis, diagnostic, and diagnostically are among the most frequently used terms in healthcare communication. Because accurate identification is the essential first step toward effective treatment or repair, diagnose describes one of the most consequential acts of knowing in both professional and everyday life.
verbTo identify the nature of an illness or problem by examining its signs and symptoms; more broadly, to determine the cause or character of any situation through careful analysis.
- To identify a disease or medical condition in a patient by examining symptoms and test results.
- To determine the root cause of a non-medical problem, such as a mechanical fault or organizational failure.
"The doctor was finally able to diagnose the cause of her persistent headaches."
"Doctors were able to diagnose the infection within hours of admitting her to hospital."
"The consultant was brought in to diagnose why the company's supply chain kept failing."
The word 'diagnose' literally means 'to know through and through' — from Greek dia (apart, thoroughly) and gnosis (knowledge).
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diagnose
Diagnose comes from the Greek verb diagignōskein, meaning 'to distinguish or discern', formed from dia- ('through, apart') and gignōskein ('to know'). The related noun diagnosis entered English in the seventeenth century via Latin and New Latin medical usage, and the back-formed verb diagnose followed shortly afterwards. The same Greek root gignōskein gives English words such as prognosis, agnostic, and cognate, all sharing the core idea of knowledge or recognition.
Related word forms
How diagnose is actually used
Diagnose is standard across formal and informal registers. In medical contexts it typically appears in passive constructions such as 'she was diagnosed with diabetes'. When used outside medicine, it often carries a slightly technical or analytical tone.
Easily confused with diagnose
A diagnosis identifies what condition someone has, while a prognosis predicts its likely course and outcome.