A General and Intuitive Envelope Theorem

About this event

Previous envelope theorems establish differentiability of value functions or policy functions only. Our envelope theorem applies to all functions whose derivatives appear in first-order conditions. For example, in Stackelberg games, the leader's first-order condition involves the derivative of the follower's policy. Similarly, we differentiate (i) the borrower's value function and default cut-off policy function in an unsecured credit economy, (ii) the firm's value function in a capital adjustment problem with fixed costs, and (iii) the households' value functions in an informal insurance economy. Our theorem accommodates optimization problems involving discrete choices, infinite horizon dynamic programming, and Inada conditions.