As the saying goes, every invention is just a combination of things that have already been invented. While this may not strictly be true, many inventions are not entirely new concepts. They are simply improvements over other inventions. When determining whether or not an invention may be patented or whether or not a product may be sold, the question of how different is different enough often arises. A different level of “different” may be required for each of these questions.
In the case where a patent already exists and you simple want to avoid infringing that patent, the question of “How different is different enough?” may be answered pretty straightforwardly. First, the patent can be reviewed to make sure it remains valid and enforceable. If it is, the claims of the patent must be read to make a determination of infringement. The claims are the numbered paragraphs at the end of the patent that actually define what the patent protects. Each claim generally comprises several elements. If a device contains each and every element of any single claim of the patent, the device infringes the patent.
In the case where a person wishes to obtain a patent on something similar to a device disclosed in an existing patent, the question of “How different is different enough?” is somewhat harder to answer. In this case we must determine whether the device is both novel and non-obvious. This means that the device cannot already exist and that it cannot be an obvious combination of previously invented components. It is novel if the exact same thing has not already been invented. And it is non-obvious if it is not a combination of features existing in the prior art, for which there is some motivation or teaching to combine.