Reduction to Practice

Reduction to practice is the step that follows conception — it is the physical embodiment of the conceived invention or the legal formalization of it by filing a patent application. There are two types: (1) ACTUAL REDUCTION TO PRACTICE — physically making and testing the invention to demonstrate that it works for its intended purpose; (2) CONSTRUCTIVE REDUCTION TO PRACTICE — filing a patent application that adequately describes and enables the invention; the filing date is treated as the date of constructive reduction to practice. Under the pre-AIA U.S. first-to-invent system, reduction to practice (combined with conception date and diligence) determined priority between competing inventors. Under the AIA first-inventor-to-file system (effective March 16, 2013), the effective filing date controls priority — but reduction to practice remains relevant for inventorship determination and understanding the patent process.

Actual reduction to practice requires: (1) PHYSICAL EMBODIMENT — the inventor must physically make, create, or build the invention; (2) TESTING — the physical embodiment must be tested sufficiently to show that it works for its INTENDED PURPOSE; (3) RECOGNITION — the inventor must recognize that the embodiment in fact works for the intended purpose. Testing standard: the level of testing required depends on the complexity and intended use of the invention. For a simple mechanical device, demonstration that it performs its function once may suffice. For a chemical compound intended for pharmaceutical use, more extensive testing (showing efficacy and at least initial safety) may be required. The testing need NOT demonstrate perfection or commercial viability — it need only show the invention is operable for its intended purpose. Weil v. Fritz (1910): using a working prototype in the intended application context constitutes actual reduction to practice.

Constructive reduction to practice occurs when the inventor files a patent application (U.S. provisional or nonprovisional, or a PCT application designating the U.S.) that adequately describes the invention — with sufficient written description and enablement to satisfy 35 U.S.C. § 112(a). The filing date of the application is treated as the date of constructive reduction to practice. The inventor does not need to have actually built or tested the invention before filing — the filing itself is the constructive reduction. Requirements for the filing to constitute constructive reduction to practice: (1) The specification must adequately describe the invention (written description requirement); (2) The specification must enable a person of ordinary skill to make and use the invention without undue experimentation (enablement requirement); (3) The claims must particularly point out and distinctly claim the invention. If the specification fails written description or enablement, the filing date may not be awarded as the constructive reduction date for that specific claim.

Reduction to practice is distinct from inventorship — a person who performs the physical work of reducing an invention to practice, but who did NOT contribute to the conception, is NOT an inventor. The mental act of conceiving the complete and operative invention is the defining act of inventorship. Example: an engineer who follows a scientist's exact specifications to build and test an experimental device did not contribute to conception of the invention — the engineer is not a co-inventor, even if the engineer's physical skill was essential to the reduction to practice. Contrast: if the engineer encountered a problem during reduction to practice and devised a solution that added to or modified the claimed invention — contributing to the conception of a new element — the engineer may be a co-inventor of the claims that include that element. Under 35 U.S.C. § 116, joint inventors need not work at the same time, or in the same place, or make the same contribution. But each must contribute to the conception of at least one claim.

Under the pre-AIA first-to-invent system, diligence was critical when a later conceiver reduced to practice before an earlier conceiver. DILIGENCE means continuously working to reduce the invention to practice from the time just before the other party's conception through the earlier conceiver's own reduction to practice — with no significant gaps in activity. If the first conceiver was continuously diligent from before the second party's conception date through their own reduction to practice, the first conceiver prevailed despite the second party's earlier reduction to practice. If there was a gap in the first conceiver's work, and the second party conceived and reduced to practice during that gap, the second party might prevail. AIA IMPACT: diligence between conception and reduction to practice is no longer determinative for priority between competing applicants under the AIA's first-to-file system. However, diligence remains relevant for: (1) derivation proceedings (showing the petitioner's earlier independent conception and diligent work toward filing); (2) pre-AIA interference proceedings for applications with effective filing dates before March 16, 2013.