common law patent

Edward ...

There is no such thing as a "common law patent". You either have a patent issued by the Patent and Trademark Office (PTO) or you don't. Now, just because the other inventor has a patent does not mean that you have violated it. Patents are intricate documents which go into some detail about what has been patented; if your invention differs enough from his, then you may not have infringed. Differences like those you list -- dimensions, fabric, door openings and the presence of a floor -- seem unlikely to be significant. After all, what good would it do to patent any invention if someone could get around your patent just by changing the dimensions? Even you admit that the inventions are very similar, and the PTO is likely to agree. It may also be that you are the first inventor and that he simply obtained a patent before you bothered to. If you can prove your priority, you might be able to have his patent invalidated and even obtain one for yourself. There are other ways to attack his patent. For example, you could argue that his invention actually falls within the scope of another, older patent. You could argue that his invention was obvious from the existing state of the art and thus not worthy of a patent. There are other such arguments that could be made. The problem for you is that most of these arguments would undercut your own position as well -- if the other invention isn't patentable and yours is very similar, then yours likely isn't patentable either. Any of these approaches is likely to be *very* costly, and you will need a qualified lawyer if you intend to fight. This is a good example of why inventors should make sure what patents are out there and try to secure their own patent *before* getting too far into the process.