In order for an invention to be patented it must meet certain criteria. It must be new, inventive and useful. It cannot be obvious to someone with a good knowledge and experience of the subject. It must be capable of being made and used in some kind of industry.
An invention is new if it is different from anything previously known to the public anywhere in the world. This means that claims are assessed against everything that is published or in use before the priority date (this information is called the “prior art base”). The difference can be small, but it must be significant in terms of how the invention works.