 Traditionally oaths were understood as a separate species of obligation-producing commitment, a “calling to witness” of God to bolster a claim to veracity on the part of the swearer. Aquinas, for example divides them into four types: Calls to witness truths of the past or present, which he calls declaratory oaths, and claims of some future conduct, which are promissory oaths. Further, oaths can be either simple invitations to witnessings, which are simply oaths, or they can be invitations to punish the swearer for default, which are curses: