A divisional patent application, also called divisional application or simply divisional, is a type of patent application that contains subject-matter from a previously filed application, the previously filed application being its parent application.[1] While a divisional application is filed later than the parent application, it retains its parent's filing date,[1] and will generally claim the same priority. Divisional applications are generally used in cases where the parent application may lack unity of invention; that is, the parent application describes more than one invention and the applicant is required to split the parent into one or more divisional applications each claiming only a single invention. The ability to file divisional applications in cases of lack of unity of invention is required by Article 4G of the Paris Convention.[2]
Once a patent application is pending, the applicant can file a new application, called a divisional, in respect of the same subject matter as the original application, and this divisional is entitled to the original application's priority date.
(Article 4G) (1) If the examination reveals that an application for a patent contains more than one invention, the applicant may divide the application into a certain number of divisional applications and preserve as the date of each the date of the initial application and the benefit of the right of priority, if any. (2) The applicant may also, on his own initiative, divide a patent application and preserve as the date of each divisional application the date of the initial application and the benefit of the right of priority, if any. Each country of the Union shall have the right to determine the conditions under which such division shall be authorized.