A system of atonement in vogue in the Church from about the end of the 8th to the end of the 11th century, whereby easier and shorter exercises were substituted for works of penance imposed by the early canons.
It originated in England and, in another form, in Ireland.
These substitutions assumed different and varied forms such as fasting, prayer, and especially alms-deeds.
This led to grave and serious abuse in as much as the wealthy began to evade the commuted penance by hiring a substitute.
This practise was severely condemned (cf. Council of Clovesho, A.D. 747).
The commutations and compensations of penitential redemptions can be regarded as true indulgences only when granted by the Church in lieu of other penances prescribed by the canons.
New Catholic Dictionary