In a co-op, the "owner" actually doesn't own their unit, but they do own shares in the company that owns the whole building, so they in essence own a share of the building itself, just not a share specific to their unit. They then lease the unit from the company... the company they partly own. Marketing materials for the Campanile from 1928 (a year before it opened) hail co-op ownership as "the most satisfactory solution of the metropolitan living problem."