What is the difference between 'open perils' coverage on a dwelling and 'named perils' on contents in an HO-3?

The HO-3 (Special Form) has a coverage asymmetry that surprises some policyholders. Coverage A (Dwelling) and B (Other Structures) are open perils — covered for any cause of loss unless specifically excluded. Coverage C (Personal Property) is named perils — covered only for specifically listed causes: fire, lightning, windstorm, hail, explosion, riot, aircraft, vehicles, smoke, vandalism, theft, falling objects, weight of ice/snow, sudden discharge of water, electrical surge, freezing, volcanic eruption. If personal property is damaged by a cause not on this list (and not a specific exclusion), there is no coverage. Examples of gaps: rust or corrosion damage, marring or scratching from non-listed causes, deterioration. The HO-5 (Comprehensive) extends open perils to personal property as well, eliminating this gap, and costs only modestly more. For homes with significant personal property value, the HO-5 is often worthwhile.