The contract clause bars depriving expected benefits, not imposing new burdens

Evidence

Only the states, and not Congress, are in terms forbidden “to pass any * * * Law impairing the Obligation of Contracts.” Here it willbe observed, the Constitution steps in to forbid not the retroactive imposition of a burden on primary conduct but the deprivation of an ecpected benefit from a previous exercise of a primary power. — Henry M. Hart, Jr. and Albert M. Sacks, The Legal Process, 3007

Categorization

• DEFINE: Sharp functional contrast: ex post facto bars burdens on conduct while the contract clause protects expected benefits — a distinction worth keeping precise.
• XREF: connects to: Conflict-of-laws rules exist to keep forum choice from altering primary law — Henry M. Hart, Jr. and Albert M. Sacks, The Legal Process: Basic Problems in…, 2959