What are the special rules of classification in CPC Definitions?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

CPC Definitions include special rules of classification that apply within specific subclasses or groups. According to MPEP 905.02, these rules are:

1. First place priority rule: “When a document is classifiable in more than one group in a scheme, the one highest in the scheme is allocated to the document.”
2. Last place priority rule: “When a document is classifiable in more than one group in a scheme, the one lowest in the scheme is allocated to the document.”
3. Common rule: “When a document is classifiable in more than one group in a scheme, the classification symbol that most completely covers the invention is allocated to the document.”

The MPEP further clarifies, “In CPC, as with IPC, in the absence of any classification rule, common rule, defined in (D)(3) above, is the governing classification rule.” This hierarchy of rules helps ensure consistent and accurate classification of patent documents.