When is something prior art against a patent?

Prior art for a patent (application) means anything published before the filing date of the patent which describes the same or a similar invention.

By IT-lawyer Arnoud Engelfriet (blog, contact).

While there are many different grounds on which a patent can be invalidated, the most common one is that the invention is found to be not novel or obvious in the light of the prior art. As the claims are used to define the scope of protection granted by a patent, this can only occur if the patent's claims are not novel or obvious. So, to get a patent invalidated, the first step is to locate documents that can be considered "prior art" against the patent's claims. Prior art basically means any disclosure of the contents of a claim, prior to the application for patent.

National patent laws provide various definitions of what constitutes prior art and in which situations. For example, not all countries recognize oral disclosures as prior art, and others provide grace periods during which the inventor may publish his invention without the publication counting as prior art against his later patent application. Additionally, the Paris Convention provides so-called priority rights, which give an inventor one year to file patent applications after he filed the first one, without endangering the novelty of his invention.

How prior art is used against a patent

A patent cannot claim something that already exists, nor can it claim something obvious. To determine this, patent examination always involves looking for prior art, earlier publications that show the invention is not new or is obvious.

One of the reasons that a patent system exists is to reward inventors for disclosing their invention to the public. This implies that an invention should be new, because otherwise the inventor would get a reward for telling us something we already know. An important aspect of the patent system therefore is the determination of novelty (and obviousness) of an invention. If examination reveals that an invention is not novel, the patent application is rejected. And even if the patent is granted, it can still be annulled by a court if the court finds that the invention wasn't novel after all.

The first step in patent examination is to search the available literature for documents that describe the invention in whole or in part. A restriction is made in this search: only documents published before the filing date of the application in question are considered. Patent practitioners call this "the state of the art". This restriction allows an inventor to publish his invention after he has filed a patent application on it, without destroying the novelty of his invention. Documents found in the search are often referred to as "prior art".

In all cases, examination of the patent application is carried out on the basis of the claims (see Determining the scope of a patent). The evaluation of a prior art document thus must also be performed by comparing it to the claims. In this document the term "invention" should therefore be read as meaning "invention as defined in one of the independent claims of a patent or application".

A prior art document is said to anticipate a claim of a patent if the prior art document describes all the features of that claim, either implicitly or explicitly. The features of the claim must be present in the same composition in the prior art. The invention is then not novel over that prior art document. Such prior art documents are often referred to as "killer prior art", although patent attorneys discussing their own cases prefer the term "relevant prior art".

If a prior art document does not describe all the features of a claim, that claim is said to be novel compared to the document. The document can still be useful as prior art, but only to prove that the claimed invention is obvious (see When is an invention obvious?). Usually, to establish that an invention is obvious, more than one prior art document is necessary.

What can be prior art

Any publication, in any form, in principle qualifies as prior art. Often earlier patents and scientific publications are used, because those are the easiest to find. But also textbooks, newspapers, lectures, demonstrations and exhibitions and any other disclosure can be used. Of course the proof of what was demonstrated or exhibited can be complicated.

Any publication

While earlier patents and published patent applications are most often cited by patent offices, any document from any source can in fact be used as prior art. It does not matter in which language the document is written, in how many copies it was made available, or whether any copies where in fact bought or read by third parties. The only thing that matters is that the document was available to the public before the critical date. A single copy of a Ph.D. thesis available in a university library counts as prior art, as would an article in the Irkutsk Daily Gazette.

Also, the intended audience for the publication is mostly irrelevant. Whether an invention is described in a a highly technical electrical engineer's journal, or in a junior high school textbook, does not matter. The textbook counts as prior art just like the journal, if both were published before the filing date of the patent application.

Any material available to the public

Something counts as prior art only if it is available to the public. It is irrelevant whether the public in fact accessed the document, or how easy it was to find the document. For instance, a paper might be published in a journal with a very small circulation, or a book might be present in the library without being mentioned in the catalog. People might give lectures and distribute handouts at a conference that costs several thousand dollars per day to attend. All these instances constitute prior art, as long as a member of the public could gain access to it without violating a secrecy obligation or doing something illegal (such as breaking into an inventor's private library).

Making available and exhibitions of products

Publicly available products also count as prior art, even though it may be very difficult to determine exactly what the product is made of or how it works. If a device is put on the market before the patent application filed on a feature in that device, the feature is no longer novel. Usually, the sale or other disposal of the product is enough to make all its features prior art for later filed applications. If the product is not sold, but only demonstrated to the public, then only those features which the public could observe count as prior art.

In the USA, selling or publicly displaying an invention counts as prior art (35 US Code 102(b)) even when the invention was completely hidden from view as part of a larger machine or article, if the invention is otherwise used in its natural and intended way and the larger machine or article is accessible to the public. But if the use was under the control of the inventor, the invention was not publicly used and so the use does not count as prior art.

Non-disclosure agreements

The inventor might want to disclose his invention to a third party before filing a patent application, for example to evaluate the commercial value or to get help in developing a prototype. If such a disclosure is done in confidence, it does not count as prior art. While a written non-disclosure agreement (NDA), signed by both parties before the invention is disclosed, is probably the best way to go, it is by far not required. As long as the inventor can prove that the disclosure was confidential, it does not count as prior art. Of course with a written and signed NDA it is easy to prove this.

A disclosure can also be implicitly confidential; that is, the recipient of the information should have known that this was confidential information. For example, when presenting your invention to a patent attorney it is not necessary to have him sign an NDA first.

Oral disclosures

Oral disclosures, such as lectures or nonconfidential discussions between the inventor and a third party, usually also count as prior art. The problem with oral disclosures is usually how to prove that they took place and what was disclosed exactly. In some cases a transcript or recording may be available. This can serve as evidence of what was orally disclosed, although establishing the date of the oral disclosure may still be difficult.

Note that the transcript itself also counts as prior art from the day it was published. Thus, if the patent application was filed after the publication of the transcript, it may be easier to use the transcript as prior art than to use the transcript as evidence of an earlier oral disclosure.

The USA regards oral disclosures as prior art only if they were made in the USA (35 US Code section 102(a): "known or used by others in this country, or patented or described in a printed publication in this or another country"). A therapeutic technique orally handed down from one generation to another by a tribe in South America can thus still be patented in the USA, despite it being publicly known (but not from a printed publication) for many years.

When is something prior art

To determine whether something is prior art, the filing date of the patent application or patent in question is crucial. If the publication or disclosure was made before the day of filing, it counts as prior art. It doesn't matter how long before the day of filing the publication was made. It is important, however, that the publication date can be established with sufficient accuracy. For example, if a patent application is filed on March 1st, 2000, a book published in 1999 counts as prior art. Its second edition from 2001 does not. An issue of a journal from "March 2000" may or may not be prior art, depending on the publication date of the journal. Many journals are distributed before the month given on their covers, but this is not always the case.

Internet publications

Internet publications are special case. As most patent offices perform their search and examination several months after filing of the application, a search on the Internet will not be of much use. In the intervening months pages on the Web may have been updated, added or removed, which makes it impossible to determine whether the invention was published on the Internet before the day of filing. But if it can be proven that a web page with a particular contents was publicly accessible the day before the filing date, then that web page will count as prior art. A site such as The Internet Archive could be very useful in such cases.

Enabling disclosure

Another requirement for document to qualify as prior art is that it is enabling. In other words, the document must enable an average skilled person to practice the invention as claimed. A science-fiction novel might describe an invention without going into details. While this will describe the basic idea behind the invention, it does not enable the skilled person to construct the invention. For example, the famous Star Trek TV series features the so-called "transporter", by which Starfleet personnel could be "beamed down" to the surface of the planet. However, no details were ever given on how the transporter was supposed to work, or how anyone could build it. If someone today were to invent a working matter transporter that operated in exactly the same way as in Star Trek, he would still be able to obtain a patent on it. The disclosure given in the TV series would not be sufficient to destroy novelty of the features of his transporter.

That does not mean that fiction cannot be used as prior art at all. If the fiction describes the invention in sufficient detail, it counts as prior art just like a technical publication would.

A famous example is the case of a method to recover sunken ships by filling them with buoyant bodies fed through a tube. According to a popular story (well, among patent attorneys anyway), the patent on this method was refused because it had already been described in a prior printed publication. Which document? The 1949 Donald Duck story The Sunken Yacht (by Carl Barks), which shows Donald and the nephews raising a ship by filling it with ping pong balls shoved through a tube. To read what is and is not true about this story, see The "Donald Duck as prior art" case.

Priority rights

If an inventor files a patent application in one country, he can file other applications in the rest of the world within one year. Those other applications then are treated as if they were filed on the date of the first application. This is called the "right of priority" and was introduced by the Paris Convention.

The Paris Convention

The Paris Convention, established in 1883, is one of the most important treaties in intellectual property law. One of the aspects of patent law it regulates is the so-called right to priority. When the treaty was established, someone who wanted to obtain patents in multiple countries had to file separate applications in each of these countries. If the invention was going to be put on the market, it would no longer be patentable in most countries, and so translations and other administrative affairs would have to be done very quickly.

To ease matters somewhat, the Paris Convention grants an inventor a priority right based on a patent application filed in one member country. If the inventor subsequently files patent applications for the same invention in other member countries within one year after filing the first one, the later applications receive a fictional filing date (the "priority date") that is equal to the filing date of the first patent application. This gives the inventor one year to prepare translations and to brush up specification and figures, and to decide in which countries he wants to file a patent application.

While today it is a lot easier to file a patent application in multiple countries (using international treaties like PCT or the EPC, and using fax machines if you're in a hurry), the right to priority is still very much in use. The main reason probably is the fact that it allows you to delay the decision in which countries to file, and that it permits changing the application after filing it. Normally, it is not permitted to make big changes to a filed patent application. However, using the Paris Convention, an inventor can draft a new patent application with all the changes he wants, and file it within one year after filing the first application, claiming the priority right of that first application. Of course the changed application should still be the for "same invention" as the original application (as you can imagine, such changes can lead to interesting discussions).

Claiming priority

If an application has a valid right to priority, the effect is that the filing date of the first application is used as the crucial date, rather than the filing date of the later application. Any publication between those two dates therefore does not count as prior art. If, however, the application's claim to priority is found to be invalid, such a publication suddenly does become prior art.

As stated above, the scope of a patent is determined exclusively by the claims. Consequently, a claim to priority must also be evaluated by looking at the claims of the later application. If all the elements of a particular claim can be found in the priority document, that claim has a valid right to priority. These elements must then also be present in the same combination as given in that claim. So if the priority application states that the combination of elements A, B, and C is essential, a claim to priority for a claim towards a combination of only elements A and B would not be valid.

A patent application can claim the priority of more than one earlier application, but all the earlier applications must have been filed within one year prior to the filing of this patent application. In such a situation, determining whether the claims to priority are valid and which claim has which priority date can be very difficult.

Grace periods

A grace period is a term of art in patent law for any time period after a publication of the invention, during which a patent application can still validly be filed. Different countries have different laws on grace periods. The USA has the most liberal regime, allowing an inventor up to one year after publishing his invention to validly patent this invention.

Grace periods for normal publications

Normally, any publication before the filing date of the patent application counts as prior art. This includes publications made by the inventor himself. So, an inventor who wants to put a product on the market must file one or more patent application(s) first. However, as filing patent applications can be very expensive it is not always possible for an inventor, especially a small one, to protect his new product adequately before going to market. Once sales of the product start taking off, he might earn the money to afford patent applications, but by then it will be too late, as his publicly available product discloses all the features of the invention(s) he wants to patent and so with count as prior art against those patent applications.

Some countries regard this situation as unfair, and have special provisions in their patent laws that offer a "grace period". Publications made during the grace period, which is usually expressed as a number of months before the day of filing, are disregarded when determining the state of the art. For example, the USA does not regard publications made less than a year before the filing of the U.S. application as prior art (35 US Code 102(b)), regardless of who made the publication. Japan provides a six-month grace period, but only for publications by the inventor himself (section 30 of the Japanese Patent Law).

Of course any such grace periods only apply in those countries. If a U.S. inventor publishes his invention and three months later files a patent application on it in the USA, Japan and Europe, the European patent application will be rejected because it is not novel in the light of the inventor's publication. European patent law does not have a grace period.

Grace periods after unauthorized disclosures

Another situation in which a grace period may be helpful is when a third party is told something about the invention in secret (for example, under a nondisclosure agreement) and then violates the NDA by revealing his knowledge to the public. This disclosure normally counts as prior art, if done before the filing date. But again, it would be unfair to have this count against the inventor. Some patent laws therefore give inventors a limited time to file a patent application after such a violation occurs. If the application is filed in that time period, the disclosure by the third party does not count as prior art.

Grace periods relating to international exhibitions

A disclosure made at a recognized international exhibition such as the World Expo also does not count as prior art (article 11 of the Paris Convention), although a certificate proving that the invention has been so displayed is usually required to be submitted to the patent office. This exception does not apply to any exhibition, but only to official or officially recognized exhibitions, as set out in the Convention on international exhibitions of 1928.

A special case: earlier filed patent applications

When someone files a patent application on an invention, other patent applications on the same invention may have been filed earlier. If the later patent application was filed before the earlier applications or patents were published (which normally happens 18 months after filing, or upon grant), the earlier applications do not count as prior art in the normal sense. However, this would lead to the situation that two people would obtain a patent on the same invention, which is undesirable. For this reason many countries have special provisions for earlier filed patent applications that were not published before the day of filing of the later application. Such patent applications are sometimes referred to as "prior rights".

Prior rights under European patent law

The prior art status of a prior right is not necessarily the same as the status of a published document. Most European countries explicitly state in their patent laws that prior rights may only be used to prove that an invention was not novel. If the invention as claimed in the later application differs even slightly from the prior right, it is novel and no further objections may be raised based on the prior right (article 56 EPC). Such a small difference is considered to be enough to make the later invention a "different" one. This way, it is prevented that two people, or even a single inventor, could obtain multiple patents on the same invention.

Prior rights under US patent law

U.S. patent law uses a different approach. 35 US Code section 102(e) states that U.S. patents filed before the date of invention can be prior art. A requirement is that the U.S. patent in question is published, either as a granted patent or as a patent application. If this is the case, and the filing date is sufficiently early, the earlier patent or application counts as prior art and can be used to attack both novelty and obviousness of the later application.

Another requirement is that the prior right in the U.S. must be owned by "another". This is interpreted very strictly: even if the two patent applications concerned have some inventors in common, if the two lists of inventors are not identical, the earlier application was made by "another". It could happen that the two patent applications are owned by the same assignee. In this case, the earlier application can still be used against later one, unless the applicant can show that the earlier application describes his own work. Usually, this means that the assignee of the later application must prove that that invention was made first.