Unfortunately there is no easy answer to the question of prior art, particularly for those who are new to the patent field. We can start off with the understanding that a particular reference or piece of knowledge will be considered to be prior art that must be overcome by a patent applicant if the patent examiner is legally allowed to use it against the applicant to reject one or more claims in a pending application. Likewise, a reference or piece of knowledge will be prior art if it can legally be used to invalidate one or more claims of an issued patent during litigation.

The trouble with explaining what prior art is stems from the fact that everyone already thinks they know what it is. Conceptually we do not want to issue patents for inventions that are not considered new, which seems fair enough. The trouble is defining what is “new.” For now, let’s just say that prior art must be a reference of some type (i.e., a patent or a printed publication) or some type of knowledge or event (i.e., public knowledge, public use or a sale of a product) that demonstrates that the invention in question is not new.

Now comes the curve ball you have probably been expecting. Not all references, knowledge or events that can demonstrate that an invention is “old” or already known can be used by examiners or during litigation against an invention. This is where the whole definition of prior art takes a turn toward an Abbott and Costello routine. Before we go to far down this path lets set some definitive rules:

• If the invention in question was described in a patent issued anywhere in the world prior to the patent applicant inventing it, then no patent can be obtained.
• If the invention in question was described in a printed publication published anywhere in the world prior to the patent applicant inventing it, then no patent can be obtained.
• If the invention were publicly known in the US, but not necessarily patented or published, prior to the patent applicant inventing it, then no patent can be obtained.

In each of these three cases we would say that the earlier reference of knowledge is prior art that prevents a patent from now issuing.

Now some more rules:

• If the invention in question was described in a patent issued anywhere in the world more than 12 months prior to a US application being filed, then no patent can be obtained.
• If the invention in question was described in a printed publication published anywhere in the world more than 12 months prior to a US application being filed, then no patent can be obtained.
• If the invention in question was publicly used in the US more than 12 months prior to a US application being filed, then no patent can be obtained.
• If the device, machine or compound in question was offered for sale in the US more than 12 months prior to a US application being filed, then no patent can be obtained.

In each of these three cases we would also say that the earlier reference, knowledge or event is prior art that prevents a patent from now issuing, but this time not because the invention was not new, but rather because an application was made in the US too late!

Now we are only a short way through the chaos that is section 102 of our patent laws, and we have seven rules that logically don’t seem to make sense. Some say things that happen anywhere in the world can be used as prior art, some say only things in the US can be used as prior art. Who created this mess? Congress, of course. But let’s not give up just yet despite Congressional involvement. Let’s discuss what is not prior art, to drill the lunacy home. More rules:

• If the invention were known outside the US but not in the US prior to invention, there is no problem and a patent can be obtained, provided no other “knock out rule” exists.
• If the device, machine or compound were sold outside the US but not in the US more than 12 months prior to the filing of a US application, there is no problem and a patent can be obtained, provided no other “knock out rule” exists.
• If the invention rights were offered for sale or license anywhere in the world more than 12 months prior to the filing of a US application, there is no problem and a patent can be obtained, provided no other “knock out rule” exists.
• If the invention were used publicly outside the US but not in the US more than 12 months prior to the filing of a US application, there is no problem and a patent can be obtained, provided no other “knock out rule” exists.

Now you are either pulling your hair out, laughing or crying. Not even our US Congress could screw something up so completely, could they? Unfortunately the answer is yes, they can, and yes they did. The truly sad thing is that what is above only goes through a handful of permutations that are found in 102(a) and 102(b), and there are still (c) through (g)!

I will spare you the gory details of (c) through (g), for now. Suffice it to say that while conceptually you can think of prior art as that what comes before an invention, it is far more complicated than that.

Armed with this basic, yet functional understanding of prior art you are ready to explore what I perceive to be the largest single problem independent inventors have when it comes to evaluating whether their inventions could be patented. See There is No Prior Art for My Invention. The reality is that there is always prior art for an invention, the questions are just how close is it to what you want to protect and what are the reasonable expectations for obtaining a patent? That is why inventors should always do their own patent search to start, but should also eventually hire a patent attorney to engage in a thorough patent search and patentability assessment.

To learn how to conduct your own patent search see Patent Searching 101 and Patent Searching 102: Using Public PAIR.