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

Anticipation rejections are based on the premise that a prior art reference discloses all the elements of a claimed invention as a single prior art reference. When a claim is anticipated, it means that the invention is fully described and enabled in the prior art, and thus there is no novelty in the claim.

The main reason that evidence of unexpected results cannot overcome an anticipation rejection is that this type of evidence is relevant only in the context of obviousness rejections. In an obviousness analysis, unexpected results can be pertinent to demonstrating that a claim is not merely an obvious variation of what has been done before; they help establish that the invention has merit beyond what was previously known. However, with anticipation, since the prior art fully discloses the invention, the concept of unexpected results does not apply. The claim can’t be saved by such evidence when the prior art itself renders it unpatentable because the novelty requirement is not satisfied.

Thus, the answer underscores the essential difference between anticipation and obviousness, establishing why evidence of unexpected results is immaterial specifically in overcoming anticipation rejections.