If one writes the main claim by using a classifying part and a characterizing portion of this claim, then the classifying part reflects the known prior art or its features and the characterizing part is the part that distinguishes the invention from the prior art.

Is the prior art in the classifying part now represented by a single document or by several documents (and their features)?


  • Even though it is the favored format at the EPO it is not strictly required
    – George White
    Oct 12, 2021 at 18:44

1 Answer 1


It is a single document, and it is the prior art that is deemed to be the closest to the claimed invention. Should the closest prior art change during prosecution, you have to amend the preamble accordingly. You are also supposed to explicitly indicate in the background section of your patent application which among all cited documents is the closest prior art, that way other parties know what is the document with the features of the preamble.

This was not part of the question, but the features of the preamble must be disclosed in a same embodiment of the prior art document.

  • Doesn’t the examiner decide what the closest thing is as part of examination ?
    – George White
    Oct 12, 2021 at 18:46
  • 2
    Yes, the examiner does that. And the examiner will ask the applicant to amend the background and the preamble of the independent claims during examination. The applicant in principle has to do this as well when filing the patent application using the prior art that he is aware of. Oct 12, 2021 at 21:41

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