Borrowing from one domain to promote ideas in another domain is a staple of constitutional decisionmaking. Precedents, arguments, concepts, tropes, and heuristics all can be carried across doctrinal boundaries for purposes of persuasion. Yet the practice itself remains underanalyzed. This Article seeks to bring greater theoretical attention to the matter. It defines what constitutional borrowing is and what it is not, presents a typology that describes its common forms, undertakes a principled defense of borrowing, and identifies some of the risks involved. Our examples draw particular attention to places where legal mechanisms and ideas migrate between fields of law associated with liberty, on the one hand, and equality, on the other. We finish by discussing how attentiveness to borrowing may illuminate or improve prominent theories of constitutional lawmaking.

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.