Richard Muller on Solutio, Solutio Idem, and Solutio Tantundem

solutio: solution, explanation, payment. In the doctrine of the death of Christ, a distinction is sometimes made between regarding his payment for sin as a solutio idem or solutio eiusdem, a payment in the same kind, namely, an exact or precise payment; or a solutio tantundem or solutio tantidem, a payment of the same value, namely, an accepted equivalent. Thus, in the first case, the solutio idem or eiusdem, Christ’s death would be regarded as a full satisfaction, effective in and of itself because it is understood to be the same (idem) as the debt. In the second case, the solutio tantundem or tantidem, as proposed by Grotius and some of the Reformed, Christ’s satisfaction is willed by God as an acceptable payment, albeit not absolutely identical to the offense but of the same value. The concept of a solutio tantundem was crucial to Grotius’s defense of the doctrine of Christ’s satisfaction against the Socinians, who had argued the unacceptability of satisfaction theory on the ground that Christ’s suffering was not the same as the penalty of death for sin. Whereas Grotius can be read as viewing the tantundem as an acceptation of Christ’s death as equivalent, Reformed advocates of this solution typically insisted on the tantundem as fully equivalent in value. See acceptatio; acceptilatio.

Richard A. Muller, Dictionary of Latin and Greek Theological Terms: Drawn Principally from Protestant Scholastic Theology (Grand Rapids, MI: Baker Academic, 2017), 339.