Patents are issued for useful innovations. While an innovation can entail an entirely new device or design, you can also obtain a patent for improving an existing design or finding a new use for an existing device, item or chemical compound. As with all patents, the proposed innovation, in this case the new use, must be truly novel, not publicly disseminated before and not obvious.
The three main patent types are utility, design and plant. Utility patents are for useful devices or ideas, while design patents primarily protect the appearance of innovations. Plant patents are for man-made plant varieties. Utility patents are granted for entirely novel devices or items, improvements to existing devices and for new uses of a known device, product or chemical compound.
It is therefore possible to patent something that already exists if you can find a new use for it. It is common, for instance, for pharmaceutical companies to be granted patents when they discover a new use for an existing drug. This new use must meet other criteria, however, that apply to all patents, including novelty, originality and usefulness.
To be patentable, an idea must meet several criteria. First of all, it must be new and unknown up to the point you devised it; the second requirement in particular can make or break a patent application. In addition to being an idea that was previously undiscovered, the invention must also have not been in the public domain. In simpler terms, even if you are the indisputable creator of a useful and otherwise patentable idea, you cannot patent it if you have publicly disseminated the information. What constitutes public dissemination of an idea is not always easy to discern. Sharing your idea with very large audiences freely, however, such as posting it on a website that can be accessed by anyone, will place the idea into the public domain and eliminate the possibility of obtaining a patent.
In addition to being new, the idea must also be original. Patent lawyers state the same principle by saying that the idea cannot be patented if it is obvious. A natural question, of course, is: "Obvious to whom"? Broadly speaking, an idea should not be obvious to someone who is an expert in the field. If you wish to obtain a patent for the use of baking soda to reduce the acidity of a particular chemical compound, the question would be whether a chemist could have discerned this property with ease. If so, the idea would not be patentable, even if the particular application has never been proposed.
Finally, a new idea must help perform a useful function to be patentable. A patent application must therefore detail not only what the patentable innovation accomplishes, but also how this accomplishment will be beneficial. The benefit can be relevant only for a very small number of potential users; only manufacturing plants that supply auto tires may find the new idea helpful, for instance. However, the idea must still accomplish something of value. This requirement can also be the source of much contention between attorneys and patent officers as it often takes an expert to see the benefits of a very narrowly focused idea. The basic principle is relatively simple, however; an invention that is merely novel and original cannot be patented unless it also does something meaningful.