Rule 43(2) defines in sub-paragraphs (a), (b) and (c) the situations where, without prejudice to the requirements of Art. 82, an application is allowed to comprise a plurality of independent claims in the same category (see F‑IV, 3.2 and F‑IV, 3.3). The express reference to Art. 82 in Rule 43(2) makes clear that the requirement for unity of invention must still be met. Where the application both lacks unity of invention and fails to comply with the requirements of Rule 43(2), the examiner may raise an objection under Rule 43(2), Art. 82 or both provisions. The applicant cannot contest which of these objections has priority (see T 1073/98, Reasons 7.2).
Alternative forms of an invention may be claimed either in a plurality of independent claims, as indicated in F‑V, 1, or in a single claim (but see F‑IV, 3.7). In the latter case the presence of the two alternatives as independent forms may not be immediately apparent. In either case, however, the same criteria should be applied in deciding whether or not there is unity of invention, and lack of unity of invention may then also exist within a single claim.
Where a single claim defines (chemical or non-chemical) alternatives, i.e. a so-called "Markush grouping", unity of invention should be considered to be present if the alternatives are of a similar nature (see F‑IV, 3.7).
When the Markush grouping is for alternatives of chemical compounds, they should be regarded as being of a similar nature where:
A "significant structural element is shared by all of the alternatives" where the compounds share a common chemical structure which occupies a large portion of their structures, or, in case the compounds have in common only a small portion of their structures, the commonly shared structure constitutes a structurally distinctive portion in view of existing prior art. The structural element may be a single component or a combination of individual components linked together. The alternatives belong to a "recognised class of chemical compounds" if there is an expectation from the knowledge in the art that members of the class will behave in the same way in the context of the claimed invention, i.e. that each member could be substituted one for the other, with the expectation that the same intended result would be achieved.
There is no need for the significant structural element to be novel in absolute terms (i.e. novel per se). Rather, this expression means that in relation to the common property or activity there must be a common part of the chemical structure which distinguishes the claimed compounds from any known compounds having the same property or activity. However, if it can be shown that at least one Markush alternative is not novel, unity of invention should be reconsidered. In particular, if the structure of at least one of the compounds covered by a Markush claim is known together with the property or technical effect under consideration, this is an indication of lack of unity of the remaining compounds (alternatives).
Objection of lack of unity does not arise because of one claim containing a number of individual features, where these features do not present a technical inter-relationship (i.e. a combination), but merely a juxtaposition (see G‑VII, 7).
Lack of unity may be directly evident a priori, i.e. before considering the claims in relation to the prior art, or may only become apparent a posteriori, i.e. after taking the prior art into consideration – e.g. a document within the state of the art as defined in Art. 54(2) shows that there is lack of novelty or inventive step in an independent claim, thus leaving two or more dependent claims without a common inventive concept (see F‑V, 9). In this respect, documents cited under Art. 54(3) should be disregarded in the evaluation of unity of invention, since they cannot anticipate the inventive concept of the application under examination.