Why does duress undermine consent?

In this essay, I discuss why consent is invalidated by duress that involves attaching penalties to someone's refusal to give consent. At the heart of my explanation is the Complaint Principle. This principle specifies that consent is defeasibly invalid when the consent results from someone conditionally imposing a penalty on the consent-giver's refusal to give the consent, such that the consent-giver has a legitimate complaint against this imposition focused on how it is affects their incentives for consenting. The Complaint Principle says that this consent is defeasibly invalid to make room for the Authorization Principle, which allows sincere authorizations to constitute valid consent, even when these are issued by an agent acting under duress. The Authorization Principle has application only in cases of third-party duress because when the consent-receiver is the source of the duress, the consent-giver is not sincerely authorizing the action.