WHAT ARE PATENT CLAIMS? WHY DO YOU NEED THEM?
[Don't want to read about this? Then skip to a HTML link to a video listed below so you can watch and learn about these important legal concepts under Patent Law.]
Patent claims are the legal definitions of your invention. When you receive a U.S. Patent grant for your invention, the claims --which are always present at the end of an issued U.S. patent-- tell the public and your competitors exactly what your invention is and how your competitors can infringe or "trespass" on your patented invention.
Patent claims are analogous to the legal plat for your real property: they outline the boundaries of what you own. So when you see a legal plat or map for the real property (i.e. "land") you own, the map lists the physical boundaries (i.e. borders or property lines) for your property.
Your patent claims do the same thing as your legal plat for real property: your patent claims outline to the public what you own for the life of your patent (i.e. for the twenty year patent term of your patent).
Prior to receiving your patent, a Patent Examiner determines if your invention is patentable based on what is listed in your patent claims. In many instances, Patent Examiners only read your patent claims to determine if they should award you with a patent grant for your invention. So patent claims are a critical part of your patent application before you receive your patent.
After receiving your patent, patent claims are crucial for determining infringement: they help you determine if a competitor is selling a product or service, or is practicing the steps (i.e. method), recited in at least one of your claims of your issued patent.
If you want understand patent infringement, I suggest a "free" YouTube video that I think is very good at explaining this legal concept well. This YouTube video is entitled: "Patent Basics - Understanding a Patent Claim," at [https://www.youtube.com/watch?v=l1Z3g7Hb01M ]. Starting at about the three minute mark (3:09 to be exact), the narrator does an excellent job in explaining patent infringement to the viewer.
Once you understand patent infringement, then this logic also extends to how Patent Examiners at the Patent Office determine how a patent claim may be patentable over the prior art.
If a single prior art patent by itself infringes a patent claim, or if a combination of two or more prior art patents infringes a patent claim, then a patent claim is not patentable ("unpatentable") over the prior art. This old axiom holds true under U.S. Patent Law: "...That what 'anticipates' a patent claim, also 'infringes' a patent claim."
In summary, patent claims are very important legal concepts to understand. Patent claims determine if you will receive a patent grant from the government and they will help a court (i.e. a judge and/or jury) determine patent infringement after the patent has been granted by the government.