A patent is a form of intellectual property which grants a legal monopoly to an inventor of a new device or process. The precise laws governing patents differ from country to country, but in general, as with other types of intellectual property, a single patent can be awarded to two or more inventors (or authors).
Intellectual property – such as copyrights, trademarks, and patents – exists to protect ideas which could be readily taken and used by others. The laws establishing rights for creators of such ideas and works are based on the principle that providing a time-limited but legally guaranteed monopoly over profiting off those ideas can provide inventors and creators with the confidence that, if they develop a new device or process or creative work, they will be able to make a profit off it. Patents and copyrights also have an expiry date, after which anybody is allowed to use the idea or work as they see fit. National laws govern patents in most countries, although in theory they must conform to a set of minimum standards in international agreements such as the Agreement on Trade-Related Aspects of Intellectual Property (TRIPS), established by member countries of the World Trade Organization.
In the United States, patent applications are processed by the U.S. Patents and Trademarks Office (USPTO), and that office has established rules governing a patentable invention by two or more authors in its Appendix R, section 1.45. The USPTO actually refers to multiple inventors applying for the same patent as “joint” inventors. The rule specifies that joint inventors must sign their name to the same patent application, rather than submitting separate applications (which would be processed as though they were separate inventors). The multiple inventors do not necessarily have to have made equal contributions to the new invention, or to any single section of the invention; however, everybody listed as an inventor must have played some identifiable role in the invention process. The rule does not specify a particular level of contribution required to be listed as an inventor, but they do specify that “each named inventor must have made a contribution, individually or jointly, to the subject matter disclosed in the provisional application.”
The USPTO rule is an application of U.S. Code (U.S.C.) Title 35, which covers patent law. Article 116 of that law similarly specifies that two or more people can apply for a joint patent, regardless of whether they worked together or made equal contributions but so long as each did make some sort of identifiable contribution. Note that as with all other patents, under American law the initial patent must always be awarded to an individual, rather than a corporation. However, patents can then be assigned to corporations – and, typically, researchers working for universities and large corporations often guarantee as part of their employment contract that they will transfer patents to anything done in the course of their work to the name of their employer.
If you have concerns about patent law in your jurisdiction, you should always speak to a lawyer. There are lawyers who specialize in patent law, and they can offer professional legal advice tailored to your specific situation.