In most patent laws, unity of invention is a formal administrative requirement that must be met by a patent application in order to proceed to grant. Basically a patent application can relate only to one invention or a group of closely related inventions. The purpose of this provision is administrative, and in particular financial, i.e. it serves to limit the possibility to file one patent application for several inventions while paying only one set of fees (filing fee, search fee, examination fee, renewal fees and so on). Unity of invention also makes the classification of patent documents easier.
At least under European patent practice and case law, lack of unity (of invention) can appear either " a priori", i.e. before taking into account the prior art, or "a posteriori", i.e. after having taken into account the prior art. An a posteriori lack of unity usually results from a lack of novelty or inventive step of the subject-matter of one independent claim.
When a patent application is objected to on the ground of a lack of unity, patent protection is not ruled out, as it would be the case if the invention was found to be lacking novelty. A divisional application can usually be filed for the second invention, and for the further inventions if any.
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