The most important part of a patent application is the claims. The claims are claims to the monopoly of the invention. This means that the application contains a few paragraphs which describe exactly what the invention itself is. These may be something similar to:
An apparatus for catching mice, said apparatus comprising a base for placement on a surface, a spring member…
…in relation to a mouse trap.
Typically there follow a number of sub-claims. These might cover non-essential elements of the mouse trap. For instance the inventor might feel that having the base made of stone might mean that the mouse trap is heavier and more effective.
Each of these sub-claims should relate to the first claim, Claim 1. In our example, this might take the form of:
An apparatus for catching mice according to Claim 1 wherein the base is formed of stone.
The reason for the centrality of Claim 1 is that Claim 1 is the invention. If Claim 1 is not new however the features found in the sub-claims (or even anywhere in the specification itself) may be added to Claim 1 to ensure that it meets the requirements of novelty and so-called inventive step – i.e. it is new and original.
This stage may happen in prosecution, another term for the process of granting of the application. Or it might happen later even after the patent has become granted, and someone somewhere feels that the patent is not valid.