Speaking to supply teachers, local authority officers, partner agencies and HMIs, there is an overwhelming agreement that a school's ethos is tangible - almost from the moment that you enter the car park.
It may be in the state of the school and its grounds, the greeting in reception, or the general demeanour of the pupils in playground or corridors.
Are there displays of work on the walls in classrooms and corridors? Do photographs, trophies and details celebrate school and individual successes in a prominent way? Does the fabric of the building look well cared for?
All of these can form a tick list of "ethos indicators", of course, and I sometimes wonder if HMIs, rather like the Queen believing the world smells of fresh paint, imagine squads of teachers pasting up each class's latest work on the classroom walls on a daily basis.
The truth is that, as the correspondent was possibly suggesting, the true measure of ethos certainly cannot be reduced to a check-list. However, this doesn't devalue its contribution; rather it points out its crucial nature as being something that drives the school's approach.
At a recent conference, one of our senior pupils was asked baldly: "How would you describe the ethos in your school?" Given there had been no preparation for this, the staff present in the group held their collective breath.
We needn't have worried. The answer when it came was better than most of us could have offered.
The pupil replied: "Our ethos is based on mutual respect between staff, pupils and everyone in the school. So, if a pupil behaves in an inappropriate manner, you are more likely to see a teacher explaining why their action is unacceptable in terms of our values, rather than just shouting at them."
She had it absolutely right. Ethos is about relationships and the values on which they are based; it's about consistency and the ability to point to the school's values statement as an operational guide rather than an aspiration.
No, you can't see it, but that doesn't mean it doesn't exist. Like the invisible wind whose reality is seen in the swaying of trees and the billowing of sails, school ethos is seen in the adults and young people who make up the learning community.
As St Andrew's latest honorary graduate might well have sung: "The answer is blowing in the wind."