If a the description of the invention in a patent application is sufficiently definite enough to allow one skilled in the art to make the invention the invention will be considered to be constructively reduced to practice, even if no working model or prototype exists. In order to win an interference proceeding it may not be enough to merely produce evidence of date of conception and date of reduction to practice. It may also be necessary for the inventor to demonstrate that he or she was diligent, which is a term of art. Diligence is only an issue with respect to invention when the first to conceive is the second to reduce to practice. In this case, in order for the first to conceive to have priority it is necessary to show diligence prior to the conception of the inventor who is second to conceive and first to reduce to practice.
Public policy favors the early disclosure of inventions.
This underlies the requirement for 'reasonable diligence' in reducing an invention to practice, not unlike the requirement that, to avoid a holding of suppression or concealment, there be no unreasonable delay in filing an application once there has been a reduction to practice.