Legal Definitions - but-for materiality

But-for materiality is a concept that was historically used in patent law to assess the significance of information that a patent applicant failed to disclose to the U.S. Patent and Trademark Office (USPTO). In essence, it asks: "If the patent examiner had known about the withheld information, would the patent still have been granted?"

If the answer was no—meaning the patent would have been rejected but for the applicant's failure to disclose the information—then the withheld information was considered "but-for material." This test focused on the objective outcome: whether the patent would have issued if all relevant facts had been known. While once applied by courts, this specific "but-for materiality" test has largely been replaced by a different standard for evaluating the materiality of withheld information in patent cases.

Here are some examples illustrating how "but-for materiality" would have been applied:

• Undisclosed Prior Art: An inventor applies for a patent on a novel type of water filter. They are aware of an existing, very similar water filter described in an obscure academic paper published years ago, which predates their invention and uses nearly identical technology. However, they intentionally do not disclose this paper to the patent examiner.

  But-for materiality would ask: If the patent examiner had known about this obscure academic paper, would they have still granted the patent for the "novel" water filter? If the paper clearly showed that the inventor's filter was not truly new or was an obvious variation of existing technology, then the patent would likely have been denied. In this scenario, the undisclosed academic paper would be considered "but-for material" because, but for its omission, the patent would not have been issued.

• Misleading Experimental Data: A company seeks a patent for a new chemical compound claimed to be highly effective in preventing corrosion. During their research, they conducted multiple tests, some of which showed the compound was only marginally effective or even failed under certain common conditions. However, they only submitted the most favorable test results to the USPTO, omitting the less successful data.

  But-for materiality would consider: If the patent examiner had seen all the experimental data, including the less favorable results, would they have still granted the patent based on the claims of high effectiveness? If the full data revealed that the compound did not consistently perform as claimed, the patent application might have been rejected. Thus, the complete, unedited experimental data would be "but-for material" because, but for its absence, the patent's validity might have been challenged or denied.

• Concealed Public Use or Sale: An individual develops a unique design for a bicycle helmet. Before filing a patent application, they publicly sold hundreds of these helmets at various sporting events for more than a year. Under patent law, such extensive public sales typically prevent an invention from being patented (known as the "on-sale bar"). The inventor deliberately omits any mention of these prior sales in their patent application.

  But-for materiality would assess: If the patent examiner had known about the extensive public sales of the helmet prior to the patent application date, would they have still granted the patent? Given the "on-sale bar" rule, the examiner would almost certainly have rejected the application. Therefore, the information about the prior public sales would be "but-for material" because, but for its concealment, the patent would not have been granted.