Conventional: Giving up your resentment towards another and your right to punish him, even though you keep the perception that he sinned against you and that you are justified in resenting and punishing him. According to the Course, this forgiveness cannot forgive, for it affirms that the other sinned and thus is worthy of condemnation (yours and his own). It also affirms that you are holier than he, because he sinned and you forgave (see T‑27.II.2:8).
ACIM: Giving up your false perception that another sinned against you and that you are justified in resenting and punishing him. Releasing this perception automatically releases your resentment and desire to punish. Releasing another not from what he did, but from “what he did not do” (T-17.III.1:5), from your misinterpretation of what he did. This can forgive, for it frees your mind of resentment and releases the other from the accusation of sin and guilt. The rationale behind forgiveness is that sin is not real. It is a wrong perception of attack. Attack has no power to do real harm (see “mind cannot attack”), because what is real (in you and in your “attacker”) cannot be harmed or changed in any way. The ultimate rationale for forgiveness is that “the separation never occurred” (T-6.II.10:7, see Atonement), that “I am as God created me,” that “God’s Son is guiltless.” Attack, then, has no effects. It is a harmless mistake, a call for love. Thus, what caused you to feel hurt was not the other’s attack, but your own misperception of his attack. Forgiveness lets this misperception go. As a result, it heals the other person of guilt, and can even heal his body. It also heals your mind of guilt and fear, for these came from your anger and resentment. It also heals you of your sense of separateness, for it takes away the perception of sinfulness that made you recoil from your brother. Forgiveness is the source of extension and the way to joining. Forgiveness is salvation. It is the central theme of the Course, and (according to the Course) of the Holy Spirit’s entire plan for salvation. See W-pII.1.