During those happy days when I was as likely to be found on a plane to Paris or Venice as on an express train heading to Edinburgh I soon learned not to discuss what the purpose of my trip was or what my role might be when I arrived at my destination. That was so I might not get involved in a conversation either with the IT expert seated on my right or the financial consultant seated to my left about the possible purposes of art criticism—nor feel obliged to respond for the umpteenth time to the following question: “Surely…