Yes, but for now what we call "depression" is those patient-reported symptoms – it cannot be any other way because at the neurochem level there may not even be

Yes, but for now what we call "depression" is those patient-reported symptoms – it cannot be any other way because at the neurochem level there may not even be any single thing that could be called "depression"! The term may not be useful except for denoting a certain syndrome, ie. a set of symptoms. Just like there's no single thing that causes the upper respiratory syndrome that we call "common cold".