Nostalgia was coined in 1688 as the name of a disease. A young doctor, Johannes Hofer, wanted a learned word for what the Swiss called Heimweh, and he built one out of Greek: nostos, the return home, and algos, pain. The symptoms listed for it included fever, an irregular heartbeat, weakness, stomach pain and melancholy, and it was said that in some cases it could kill. Military doctors went on diagnosing it long after Hofer. Somewhere along the way the word left medicine and changed sign, and now it is something we choose on purpose: an old song, a sweet they have started making again, a film set in the year we were twelve. Nobody runs a fever from it. What strikes me is that the illness was always about a place, a valley you could in principle walk back to. The kind we kept is mostly about a time, which has no road back to it. The disease, at least, had somewhere to go. What we kept is the version with nowhere to go, and we decided to enjoy it.