Criteria for patentability
The exact criteria for patentability vary between countries, and vary within countries by whether you look at patent office granting or court rulings, but the theories behind the general criteria are quite similar around the world. Some specifics will be found on pages about each patent office (such as USPTO, EPO).
The general criteria are:
- unobvious or have an "inventive step"
- useful or have "industrial application"
- patentable subject matter
The last one is what's really interesting to us.
 1. New / Innovative
The invention must be novel. In industry this is known as the "duh" clause. One example is the KSR v. Teleflex case, where the patent in question covered the shape of a lever. In effect the invention must not have been previously invented. This is not simple however, as the rules disallow certain types of evidence, so it is possible to patent something that has been in general use for years prior to the patent being applied for.
 2. Unobvious
Non-obvious means that the idea shouldn't be obvious. Simple modifications of existing devices are not allowed, nor are combinations of existing components. An example would be the motorcycle. If an automobile already exists, taking the engine from an automobile and mounting it on a bicycle frame to make a motorcycle will not be patentable. Lawyers however can write patent applications to obscure the obviousness factor, and sometimes do.
 3. Useful
Useful. This is known as "You can't fool Mother Nature" clause (from the Chifton Margarine commercials of the 1970's). In simple terms, the invention has to work. If it doesn't work, it's not eligible for patent protection. While this sounds like a no brainer, a lot of patents are issued by the USPTO for inventions that cannot and do not work, as they break natural laws.
 4. Patentable subject matter
- (see: patentable subject matter)
The invention must be something that the patent office can legally issue a patent for, this is defined in the regulations, but generally it is taken to be a physical invention. There is considerable argument at the present time about "business method" patents, which according to the in re Bilski ruling are disallowed, however it is being argued by Gene Quinn that the only requirement is that a computer be included in the application for the patent to be issued. Patent lawyers make money from filing patent applications, and herding them through the process, and thus have an interest in the range of patentability being as wide as possible. This may not be in the best interests of society as a whole.
 Other formalities
In addition to the 4 criteria above there are two other rules requirements for applications:
- Prior art must be listed. If prior art is not listed, and it is provable that the filer knew about the prior art the patent may be invalidated. Where this is most important is with the obviousness clause, as it may be decided that based on the prior art that the invention was obvious, and therefore not eligible for patent protection.
- The patent application must contain a description that would allow a person with "knowledge of the art" to build the invention. Deliberate obscuration of the description to block someone from building the device is not allowed (note that this is a also common complaint about software patents, that the description is not clear enough to allow someone to build a device).
 Non-standard "quick" patents
Some countries have two types of patent, the normal kind and a special type of "quick" patent that is granted without anyone examining the application. This page doesn't deal with "quick" patents, just the normal sort. The validity of those "quick" patents happens only when the holder tries to enforce them. Countries where such systems exist include Australia, South Africa, and previously Netherlands. The media sometimes misunderstand this and think that the patent office has examined and accepted an application for something extremely trivial, but in truth they're just pieces of paper that would be invalidated the moment anyone tries to enforce them.
 Related pages on en.swpat.org
- Wikipedia: Patentability
- Bitlaw: Patent Requirements (USA)
- German original: Patentgesetz.de on "technical teaching" (English translations[?]: Google, bing translator) - The German equivalent of "inventive step"
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