The statutory subject matter provision of the United States patent code is one of that law's murkiest provisions. It has been the subject of repeated cases before the United States Supreme Court. Despite this, confusion and disagreement among the lower courts remains substantial. Much of the literature agrees that the law is in disarray. This paper isolates and treats one such problem: that of dealing with so-called "hybrid" inventions. Hybrid inventions are those that consist of both statutory and non-statutory elements grouped together. As such, their basic nature presents a classification problem. Hybrid inventions are mongrels, neither purely statutory nor purely non-statutory. Thus, it is not possible to categorize them with the usual analytical tools. And yet they must be categorized. The statutory scheme is itself binary; it provides no middle ground between statutory or non-statutory inventions. Every hybrid invention therefore presents the task of determining which character of the invention is to control in the determination of patentability.
R. Carl Moy, Statutory Subject Matter and Hybrid Claiming, 17 J. Marshall J. Computer & Info. L. 277 (1998)