Almost every constitution in the world confers a power to pardon.  Pardon powers are found in the constitutions of old states and new states, Western states and non-Western states, states with a Christian tradition and states without one. Pardon powers are part of the constitutions of states as diverse as France, Indonesia, Peru, Russia, the United Kingdom, and the United States. 

Pardon powers share several features. First, the exercise of the power has the result of lifting or lessening criminal liability. Second, the power achieves this result not by changing the law, but by setting it aside in a particular case. Third, the power is held by a branch of government other than the judiciary – the executive, normally, or the legislature, less commonly. Finally, in its traditional mould, a pardon power is wholly arbitrary. Its use is unreviewable and unconstrained. (For recent departures from this traditional form of the pardon power, see my post here.) 

So understood, pardon powers seem to conflict with two of the most basic principles of constitutionalism. Contrary to the separation of powers, a pardon power gives to a branch of government other than the judiciary a role in determining criminal liability in particular cases. Contrary to the rule of law, a pardon power is traditionally neither controlled by nor ruled by law.  

Hence the pardon paradox: one of the most common constitutional power is at odds with some of the most fundamental constitutional principles. Pardon powers are everywhere but seem to properly belong nowhere. I argue that the paradox has a solution. Appearances notwithstanding, pardon powers threaten neither the separation of powers nor the rule of law. My argument has three steps.