What is the exception to the rule that a reference must be prior art?

The exception to the rule that a reference must be prior art allows for the use of later publications to show factual evidence in certain circumstances. As stated in MPEP 2124:

“In certain circumstances, references cited to show a universal fact need not be available as prior art before applicant’s filing date.” These facts can include characteristics and properties of a material or scientific truisms.

This exception allows examiners and attorneys to use more recent publications to support arguments related to the state of the art at the time of filing, without those publications necessarily qualifying as prior art themselves.

To learn more:

• prior art
• patent examination
• universal facts
• scientific truisms