The claims of a patent are its boundaries, defining the scope of exclusion. This boundary function of claims is undermined by the fact that claims can be changed throughout the life of the patent, thereby moving the patent boundary. A boundary that can be moved at-will is one that the public cannot rely upon.
This Article explores the problems of malleable patent boundaries. If a claim can be amended to permit a patentee to capture something he did not foresee when filing the patent application, the amendment confers an unexpected windfall that did not contribute to incentives to invent before filing. If a claim is amended so that a patentee can capture something he did foresee but mistakenly failed to claim initially, the amendment allows the patentee to shift the loss of his own mistake to third parties. Either way, the amendment is inefficient.
This Article proposes that patent boundaries should be fixed upon patent issuance, and postissuance claim amendment disallowed. Because claims before issuance do not create public reliance, preissuance amendment should be retained. Nonetheless, the possibility of inefficient windfalls requires that preissuance amendment not be given retroactive priority in order to limit the ability to capture later developments.