To “commute a sentence” is the power to substitute a sentence imposed by the judiciary for a lesser sentence. In other words, it means the power to reduce or lessen a sentence resulting from a criminal conviction. For example, a ten-year sentence may be commuted to a five-year sentence. It is a part of the broad clemency powers over federal offenses granted to the President of the United States under the U.S. constitution. Similarly, the state constitutions grant the governor clemency power over state offenses.
Cases such as this one from Illinois explain that “power to commute a sentence is the power to remove a sentence imposed by the judiciary and replace it with a lesser sentence.”
A sentence may be commuted for good behavior, illness, old age, or when the sentence is unreasonably harsh in comparison to other similar cases.
See: Commutation
[Last updated in June of 2021 by the Wex Definitions Team]