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If you file a provisional patent purely to try and protect yourself, wouldn't that document the "invention" sufficient as such to be considered prior art? And if prior art is a valid defense, is it necessary to even file a full patent? In other words...

Is a provisional patent as prior art a sufficient defense from someone else who might assert theirs for the same "invention", provided your provisional filing was filed first?

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Documenting an invention in a way that never sees the light of day does not create prior art. A provisional application (it is not any kind of a patent, just an application) is not "published" and, if not followed up by a non-provisional application, never does see the light of day. If you are interested in a defensive publication you would want something that an examiner is likely to see that keeps others from getting a patent in the first place. Having ammunition in your back pocket that might be used in an invalidity defense in case you are sued just changes the probability of who wins in an expensive future legal action.

If you do follow through and file a nonprovisional that cites the provisional and that application gets published or becomes a patent then the provisional will be prior art. (One of the few board of appeals cases that is precedential - ex parte Yamaguchi)

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very good point - so what would be the preferred (cheaper) route for an anticipated future defense? Defensive publication (about $150?) just to get the invention out into the wild? Or, a cobbled together (cheaply) non-provisional application that contains sufficient quality to be accepted; and then abandon it as soon as it enters prosecution? Keeping in mind there is NO intent to ever complete the patent process, just protect one's self from frivolous legal suits. – Ron J. May 20 '13 at 13:38
There is a good answer to this already posted at… – George White May 20 '13 at 16:42

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