Mental health diagnoses are often assumed to name underlying diseases in the way that a fracture names a broken bone. They are better understood as agreed groupings of symptoms that tend to travel together, assembled for practical purposes.
The categories were built by consensus, not discovery
Classification systems are produced by committees of clinicians and researchers who review evidence and negotiate where the boundaries between categories should sit.
The resulting definitions specify how many features from a list must be present, for how long, and with what degree of interference in daily life before a threshold is crossed.
Those thresholds are judgements rather than measurements, and they shift between editions as the evidence and the arguments change.
Grouping serves real functions
Shared categories let clinicians in different places mean the same thing by the same word, which is a precondition for research being comparable at all.
They also connect a presentation to a body of evidence about what tends to help, which is the practical value of a diagnosis to the person receiving it.
Services, funding and legal protections are organised around these categories too, so the labels carry administrative weight beyond the clinical.
The categories overlap heavily in practice
Many people meet criteria for more than one category simultaneously, and the same underlying features appear across several definitions.
Two people with the same diagnosis can share few symptoms, because the criteria require a number of features from a list rather than a specific combination.
This is a structural consequence of defining categories by counting features, and it limits how much a diagnostic label can tell you about an individual.
Biology has not confirmed the boundaries
Decades of work looking for markers that distinguish one category from another have not produced tests that reliably separate them.
Genetic findings point the other way, with risk factors distributed across categories rather than mapping neatly onto individual ones.
Alternative frameworks organised around dimensions of functioning rather than categories are actively researched, though none has replaced categorical diagnosis in practice.
How to hold a diagnosis sensibly
A diagnosis is best read as a summary of a pattern and a pointer towards what has helped others with a similar pattern, not as an account of what is wrong at a physical level.
That reading makes revision unsurprising: a diagnosis changing over time reflects the presentation changing or being clarified, not an earlier mistake.
It also leaves the person's own account intact, since the category was assembled to organise clinical work rather than to describe an individual life.