Old buildings and preservation

The honest answer is that no city can keep everything, so the real question is which buildings earn their place. I'd use two tests. First, uniqueness: a building that could exist anywhere defends itself poorly, but one that carries a story only this city can tell — a colonial post office, a wartime factory — is irreplaceable evidence. Second, usefulness: buildings survive best when they still do something. A preserved building with no function becomes a burden and eventually a ruin, whereas an old market that still trades pays its own way. Where I'd disagree with strict preservationists is on freezing whole districts: cities are for the living, and a district that cannot change slowly becomes a stage set for tourists rather than a place where people actually live.