In a closely-watched patent case before the Supreme Court, i4i has fired a brief at Microsoft saying that the latter wants to overturn a century of precedent in patent law.

i4i is a Canadian software firm that originally filed suit against Microsoft in 2007. The crux of the case was a patent i4i had filed for separating formatting from text in a word processor. The original patent was filed in 1994. The court will hear argument s on April 18.

Microsoft asked the Patent and Trademark Office to re-examine the patent. The first time the PTO confirmed that i4i's patent was valid. The second time it declined to review the patent at all. Microsoft argues that the patent isn't valid because there existed similar technology before (known as 'prior art'). In addition, the standard of proof for the validity of a patent should be lowered from clear and convincing to preponderance of evidence. In the courts, the former is a much higher standard of proof.

i4i says in its brief that changing the standard of evidence would undermine the presumption that a patent is valid when it is challenged. In addition, i4i says the clear and convincing standard is codified in law and has been since the 1950s.

Meanwhile, i4i won its case in the Federal District Courts, and Microsoft was ordered to pay $290 million. Microsoft eventually asked the Supreme Court to hear the case.

Microsoft has thus far been supported by a number of technology firms including Google, Hewlett-Packard, Dell and even Wal-Mart.