Patent infringement may be direct, indirect, or contributory. Direct patent infringement occurs when a patented invention is manufactured, used, offered for sale, sold, or imported without authorization. Indirect infringement occurs when one person intentionally encourages another to directly infringe a patent. Contributory infringement occurs when a person intentionally sells or supplies an item for only one use in conjunction with a patented invention. Good faith or ignorance are not defenses to an allegation of direct infringement, but they can be used to defend indirect or contributory infringement.