Court therefore had to set a standard for when an invention would be considered complete enough to be "on sale". The court's decision The Court, in a unanimous opinion written by Justice John Paul Stevens, noted that an invention can actually be patented before it is reduced to practice, because the "invention" occurs when the inventor has a fully formed idea of how the invention will be made. Pfaff could have patented his idea based on the drawings that he had shown to Texas Instruments, because they were complete enough to allow another engineer to build the invention from the designs. Furthermore, if an invention could be sold before it was reduced to practice without any consequence, then inventors would be able to evade the time limits placed on the patent itself by simply delaying the construction of a working model. This would, in turn, delay new inventions from reaching the public, undermining the primary goal of the patent system, "[t]o promote the Progress of Science and useful Arts..." Based on these considerations, the Court concluded that the "on sale" bar applies if two conditions are met: 1. That the product was the subject of a commercial offer for sale; and 2. That the product could have been patented at that time, either because it had in fact been reduced to practice, or because it was sufficiently well described for another person skilled in the art to build the invention from the designs. Because these conditions were satisfied, the Court held that Pfaff's patent was invalid. See also List of United States Supreme Court cases, volume 525 List of United States Supreme Court cases Lists of United States Supreme Court cases by volume References External links 1998 in United States case law United States patent case law United States Supreme Court cases United States Supreme Court cases of the Rehnquist Court