A diagnosis is often received as an explanation for why someone feels as they do. In psychiatry the categories describe patterns of experience, and the difference between describing and explaining matters considerably.
The categories are defined by symptom clusters
Diagnostic manuals specify a list of experiences and behaviours, a minimum number required, a duration, and a requirement that functioning be affected.
No biological test confirms or excludes the diagnosis, because none currently exists with the accuracy such use would require.
Which means the category is an agreement about which patterns should be grouped together, arrived at by committees reviewing evidence and revised across editions.
Description can still be useful
Grouping matters because treatments have been tested against these groupings, so a diagnosis connects a person to a body of evidence about what has helped similar presentations.
It also provides shared language between clinicians, access to services, and in many systems the basis on which care is funded.
A category with no known cause can therefore still carry real predictive information about course and treatment response, which is what makes it worth having.
The explanatory trap is easy to fall into
Saying that someone cannot concentrate because they have a condition defined partly by difficulty concentrating restates the observation rather than accounting for it.
This circularity is unavoidable when categories are descriptive, and it becomes a problem only when the label is treated as an identified mechanism.
The practical cost is that inquiry stops, since a name that feels like an explanation discourages asking what else is contributing.
The boundaries are contested and mobile
Categories are added, merged, split and removed between editions, and thresholds for severity and duration shift with them.
Symptoms also cross categories extensively, so a person meeting criteria for one condition frequently meets criteria for others, which is common enough to be expected rather than unusual.
Research funders have consequently supported alternative frameworks organised around measurable dimensions such as attention and threat response, which cut across the existing categories.
What this means for someone receiving one
A diagnosis is best read as a summary of a pattern and a route to appropriate treatment, not as a statement about identity or about a fixed biological fact.
It can be revised as the picture becomes clearer, and revision reflects new information rather than an earlier mistake.
Questions about a specific diagnosis belong with the clinician who made it, since the reasoning behind an individual assessment is not something general description can supply.