In deciding validity of patents through the obviousness test, the term PHOSITA keeps popping up. It means "person having ordinary skill in the art" and is actually a legal fiction (assumed fact). He does not have to always exist in a case, but is taken as a guideline of skill level to determine non-obviousness. Otherwise, we would know when to determine if something is non-obvious.
It was mentioned in Patently-O that we may think that the education level of the inventor is relevant to determining the PHOSITA skill level, but it should actually be excluded. The PHOSITA is simply a skilled worker (with common sense, of course, and not a robot), and should not be considered someone capable of making the invention (someone really smart). However in the KSR case, the PHOSITA figure was further expanded to be creative when looking at prior art, at least able to think slightly out of the box. That is to say, for example, a bottle invented to store water can be used to store other things, such as flowers, but not have led to being used as the body of a water-propelled rocket launcher (a bit far-fetched I know, but I could not think of anything else).
Certainly, this definition of a PHOSITA is ambiguous depending on the case, but I believe it should be kept that way. Every case can be very different and setting a stricter definition could render it biased to or against some group of cases. Even in the legal world where the law is constantly updated based on new judgement, some things are best left untouched, lest there be no case to fight anymore.
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