The first step, conception includes both the initial Eureka!-moment and a mental formulation of a complete solution to the problem in such a way that enables a person of ordinary skill in the relevant science to practice the invention without undue experimentation.

For example, Thomas Edison’s conception of a light bulb included both the initial Eureka!-moment but also the mental process whereby Edison realized that an electric current caused certain filaments to glow when in a vacuum, this glow could be controlled and could produce light. At that point in time, Edison had in his mind the conception of the invention. He knew how to use a glass bulb as a vacuum chamber, how to string a filament between two conductors inside the bulb, how to conduct current to cause the filament to emit light and thus, conception was complete. (Note: the precise material of the filament was not necessary for "conception").

The second step, reduction to practice, can occur in two ways: either an actual reduction to practice or a constructive reduction to practice. Actual reduction to practice occurs when the inventor creates a physical embodiment of the invention, such as a working prototype. However, a working prototype is not the only suitable example of an actual reduction to practice. Actual reduction to practice occurs when the invention evidences sufficient testing to work for its intended purpose.

Constructive reduction to practice occurs upon filing a patent application. A patent application must include enabling disclosure and the best mode of practicing the invention pursuant to 35 USC §112. This establishes a prima facie case of reduction to practice. Of course, the applicant may establish an earlier date of reduction to practice by evidencing the earlier actual reduction to practice.

In addition, an inventor must show diligence between the initial conception and the ultimate reduction to practice. A dilatory inventor may loose future patent rights if the time and activities between conception and reduction to practice are not reasonable under the circumstances. For example, if an inventor conceives an invention first but does not diligently work to reduce it to practice and another person independently conceives the same invention at a later date and diligently reduces it to practice, the second inventor will be granted the patent.

Diligence and actual reduction to practice may be evidenced by a good laboratory notebook or similar documents. Should evidence of diligence and the earliest date of reduction to practice be required, then adequate descriptive drawings, building a prototype, and filing a patent application can save the day.

It is also important to know that the actual reduction to practice need not take form of the ultimate commercial embodiment of the invention. As long as the inventor can show that the invention solves the problem it set out to solve, or otherwise works for its intended purpose, the most commercially viable solution need not be demonstrated.

Ultimately, an invention is patentable when conception, diligence, reduction to practice can all be demonstrated. Timely filing a patent application creates a prima facie case of conception, diligence, and reduction to practice.