What is the main reason an anticipation rejection cannot be overcome by evidence of unexpected results?

Anticipation rejections are based on the principle that a single prior art reference already contains all the elements of a claimed invention as required by 35 U.S.C. § 102. Therefore, if a claim is found to be anticipated, it means that the prior art reference discloses the exact invention claimed and does so before the filing date of the application.

In this context, evidence of unexpected results cannot be used to overcome an anticipation rejection because unexpected results are typically relevant to showing non-obviousness under 35 U.S.C. § 103. In cases of obviousness, an applicant can strengthen their argument by showing that their invention provides advantages or unexpected benefits compared to the prior art.

However, when a rejection is made on the basis of anticipation, the focus is solely on whether the claimed invention is present in a single prior reference. Thus, the argument around unexpected results does not change the fact that the prior art reference has already disclosed the entire claimed invention, making it impossible to overcome the rejection based on that evidence.

This is why the position regarding the applicability of evidence of unexpected results aligns specifically with obviousness rejections rather than anticipation rejections.