The legal issue revolves around a special rule, created by the Federal Circuit. It applies only to patent cases and not to other types of civil cases involving property rights, and it stacks the odds in favor of the patent holder, Culbert explained. A higher standard of proof is required to overturn a patent than the standard of proof required for other civil matters. For patent cases, the standard to overturn a patent is that there must be "clear and convincing" evidence that shows a patent should not have been issued in the first place, whereas in other civil cases the standard is a "preponderance of the evidence."

That special rule originally included a punishment, too: The courts would issue an automatic injunction against selling the disputed product or service if the defendant was found to have infringed. In a case involving eBay (eBay v. MercExchange, 2006), the Supreme Court decided that injunctions should not be automatic. Microsoft is now arguing to eliminate the special rule that creates a higher standard of proof to overturn a patent, too.

"Microsoft wants the same burden of proof to apply to patents that applies to other civil cases," Culbert said.

Steve Chang, a patent attorney from national law firm Banner & Witcoff, attended Monday's hearing and characterized the discussion as lively, sprinkled with chuckles. While the justices didn't tip their hand, there were some questions over i4i's position. 

"It's kind of like reading tea leaves," Chang told Network World. "The questions were not hostile to one side or other, but it was clear that some justices, like Justice Alito, were questioning what the statuary support would be for the 'clear and convincing' standard. Justices Ginsberg and Sotomayor asked if the Patent Act was passed in 1952, and the Federal Circuit was created in 1982 and the 'clear and convincing' standard came along after that, what happened in the first 30 years?"