PCT rules stipulate that no International Searching Authority is required to search and no International Preliminary Examining Authority is required to examine an international application if its subject matter is "scientific and mathematical theories" ( PCT Rule 39.1 and PCT Rule 67.1) National and regional patent offices prohibit the patenting of scientific or mathematical theories. For example, U.S. courts have decided that "scientific principles," "laws of nature," "abstract ideas," and "physical phenomena" are unpatentable. They are considered "manifestations of . . . nature, free to all men and reserved exclusively to none" [Diamond v. Chakrabarty, 206 USPQ 193 (1980)]. For this reason, USPTO rules deny patentability to such discoveries. EPO rules likewise deny patentability to scientific or mathematical theories in the abstract.
Because one of the primary advantages of filing an international application is that a thorough search and preliminary examination will provide some assurance that national applications will be successful, an applicant may be well advised not to file an international applicant if the subject matter falls into the above areas. If the USPTO ISA or IPEA conducts the international search or preliminary examination, however, it will search and examine all subject matter searched and examined in U.S. national patent applications.