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The Inventor's Mentor

July 2008

Conception Date vs Filing Date

The United States is the only country in the world where an inventor is defined as the person who first conceives of an invention. In all other countries, he is defined as the person who files the invention first.

A person shall be entitled to a patent unless …the invention was made in this country by another inventor who had not abandoned, suppressed, or concealed it. In determining priority of invention … there shall be considered not only the respective dates of conception and reduction to practice of the invention, but also the reasonable diligence of one who was first to conceive and last to reduce to practice, from a time prior to conception by the other. (35USC102(g))

In essence, if two persons file for a patent at different times, the one who files last has the burden of proof to show that he conceived of the invention first and that he exercised due diligence in reducing his invention to practice. In other words, he has not abandoned, or hidden his invention and that he has exerted a continuous and sustained effort in the development of his invention and in the building of a working prototype or in the filing of a patent.


As you can see, the law leaves a lot of questions open to interpretation and has resulted in countless lawsuits in US courts. What kind of documentation and how detailed should it be to prove conception? How well should the prototype work? How intense should the continuous effort be? Is the inventor entitled to a vacation? How long can the vacation be?

With the aim of simplifying litigation, there have been numerous attempts to change the US patent law to make it conform to all other countries: make the US a “first-to-file” country. How would such a change affect the little inventor? On the one hand it would favor large corporations which employ large teams of patent attorneys to write and file patents as soon as engineers and scientists come up with ideas. On the other hand, the simplification of patent litigation would certainly favor the little inventor.

One of the greatest inventions of all times, the telephone, was lost by Elisha Gray to Alexander Graham Bell when the Patent Office determined "while Gray was undoubtedly the first to conceive of and disclose the …invention,…his failure to take any action amounting to completion until others had demonstrated the utility of the invention, deprives him of the right to have it considered."


Even though “actual reduction to practice” i.e., building a working prototype, may help you in better refining your idea, this step is not required by the law: all that is needed is “constructive reduction to practice”, that is filing a patent that includes a written description of your invention with enough details to enable a “person having ordinary skill in the arts” to build it and to use it. This description should also include at least one “best mode” of implementation.

In summary, he who snoozes, loses. You don’t want to be the last to file and have to fight an uphill court battle to prove that you are the first to conceive. If you think you have a good idea, work assiduously on it and file as soon as you feel certain that the invention is mature enough.


Next month we’ll discuss another topic. Stay tuned.


For archived newsletters and a lot of information for the small inventor go to: If you have any question you can contact me at (858)259-2226 or email me at This newsletter should not be construed as legal advice. ©2010 by George Levy.








This newsletter should not be construed as being legal advice. ©2008 by George Levy