Abstract: Contractual duress, unconstitutional conditions, and blackmail have long been puzzling. The puzzle is why these doctrines sometimes condemn threatening lawful action to induce agreements but sometimes do not. This Article provides a general solution to this puzzle. Such threats are (and should be) deemed unlawfully coercive only when they are contrived, meaning that the threatened action would not have occurred if no threat could have been made. I show that such contrived threats can be credible because making the threat strongly influences whether the threatened action occurs. When such threats are uncontrived warnings, meaning that the threatened action would have occurred even if no threat could have been made, they are not coercive and can only benefit the agreeing parties. However, sometimes (as with blackmail) agreements produced by uncontrived warnings are also unlawful on the ground that they harm third parties. The contrived-threat test explains why the Medicaid-defunding threat in the Affordable Care Act was unconstitutional. It also explains why the recent King v Burwell conclusion—that the Affordable Care Act does not withhold tax credits from states that do not create insurance exchanges—would have been constitutionally required even if it had not been required by the statutory text.