Rule 43(1)(a) and Rule 43(1)(b) define the two-part form which a claim must have "wherever appropriate".[Rule 43(1); ]

The first part or "preamble" needs to contain a statement indicating "the designation of the subject-matter of the invention", i.e. the general technical class of apparatus, process, etc. to which the invention relates, followed by a statement of "those technical features which are necessary for the definition of the claimed subject-matter but which, in combination, are part of the prior art". This requirement to state prior-art features in the first part of the claim is applicable only to independent claims and not to dependent claims (see F‑IV, 3.4). It is clear from the wording of Rule 43 that it is necessary only to refer to those prior-art features which are relevant to the invention. For example, if the invention relates to a photographic camera but the inventive step relates entirely to the shutter, it would be sufficient for the first part of the claim to read: "A photographic camera including a focal plane shutter" and there is no need to refer also to the other known features of a camera such as the lens and view-finder.

The second part or "characterising portion" needs to state the features which the invention adds to the prior art, i.e. the technical features for which, in combination with the features stated in the first part, protection is sought.

If a single document in the state of the art according to Art. 54(2), e.g. cited in the search report, reveals that one or more features in the second part of the claim were already known in combination with all the features in the first part of the claim and in that combination have the same effect as they have in the full combination according to the invention, the division will require that such feature or features be transferred to the first part.

Where, however, a claim relates to a novel combination, and where the division of the features of the claim between the preamble and the characterising part could be made in more than one way without inaccuracy, applicants must not be pressed, unless there are very substantial reasons, to adopt a different division of the features from that which they have chosen, if their version is not incorrect. If the applicant insists on including more features in the preamble than can be derived from the closest available prior art, this is accepted.

If no other prior art is available, this first part of the claim could be used to raise an objection on the ground of lack of inventive step (see G‑VII, 5.1, last paragraph).