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Patents have a maximum life of 20 years and, therefore, a 20-year potential monopoly. Patents that are just beginning their life and which have longer to run on the their potential monopoly position understandably will have more value. It is rare that a patent nearing the end of its term will cause a great threat to its competitors. It is almost certain that they will have devised technologies or products of their own by then that will not interfere with the patent owners monopoly position. In addition, one has to take into consideration the potential business life of a patent, i.e., the duration, which a patent is likely to be economically useful, if other subsequent patents are providing better alternatives to it.

There are three types of different patents (1) Utility Patents: Issued for the invention of a new and useful process, machine, manufacture, or composition of matter, or a new and useful improvement thereof, it generally permits its owner to exclude others from making, using, or selling the invention for a period of up to twenty years from the date of patent application filing ++, subject to the payment of maintenance fees. Approximately 90% of the patent documents issued by the USPTO in recent years have been utility patents, also referred to as "patents for invention." (2) Design Patents: Issued for a new, original, and ornamental design for an article of manufacture, it permits its owner to exclude others from making, using, or selling the design for a period of fourteen years from the date of patent grant. Design patents are not subject to the payment of maintenance fees. (3). Plant Patents: Issued for a new and distinct, invented or discovered asexually reproduced plant including cultivated sports, mutants, hybrids, and newly found seedlings, other than a tuber propagated plant or a plant found in an uncultivated state, it permits its owner to exclude others from making, using, or selling the plant for a period of up to twenty years from the date of patent application filing. Plant patents are not subject to the payment of maintenance fees.