One type of property damage that may occur is loosely titled "nuisance." The theory of nuisance law differs substantially from most other personal injury theories in that the focus is on the interests of the plaintiff, rather than the conduct of the defendant. Nuisance law is divided into two categories: private and public. A private nuisance is defined as a thing or activity that substantially and unreasonably interferes with the possessor's use and enjoyment of his or her property. In some cases, this interference may be a physical interference that is damaging to the property, such as the destruction of crops or pollution of water. The interference may also be more ethereal and affect the plaintiff's comfort or convenience, without doing actual physical harm to the property itself. However, if the interference affects the plaintiff only personally, a valid cause of action will not lie. The interference must be with the use and enjoyment of the land.