The doctrine of equivalents began as a tool creating judicial flexibility to shield patent holders from piracy through minor variations on their inventions. Over time, two trends have transformed it from shield to sword. First, plaintiffs have persuaded courts to allow claims of infringement by equivalents even where there is no evidence of copying or other fraud. Second, as juries have decided more and more infringement cases, their sympathy for patent holders has had a greater impact on equivalents cases. Together, these trends have worked a gross distortion on the doctrine of equivalents. The doctrine should not be used to extend patent coverage, leaving the public unable to determine the exact scope of a patent's claims. Instead, application of the doctrine should be limited to cases where fraud or other equitable factors justify departure from the patent's terms. Further, decisions on infringement by equivalence should be made by judges in their equitable capacity, not by juries.
Peter K. Schalestock, Equity for Whom? Defining the Reach of Non-Literal Patent Infringement, 19 SEATTLE U. L. REV. 323 (1996).