Patent Validity
A patent which was not novel and inventive at its priority date is not valid. If someone is threatened with patent infringement, the first thing to do is to examine it critically to determine whether it is valid.
In addition, a patent which contains additional information to that included in the application as originally filed, it also not valid. Furthermore, a patent that does not describe the invention in sufficient detail for a skilled man to be able to work the invention is also not valid.
The application process for obtaining a patent includes an examination of the novelty and inventiveness of the invention. Nevertheless, not only are patent examiners not infallible, but should also give patents benefit of the doubt. It is sometimes possible to find prior art that the examiner has not found, or has mis-interpreted, to show that the invention lacks novelty or inventiveness.
With good arguments as to why the patent is invalid, there is a reasonable prospect that a patentee can be persuaded to go away or at least grant a licensee. Nevertheless, determined patentees with a deep pocket may be hell-bent on suing, then there is little option but to run away or stand and fight.