Double-Index Temporal Semantics and Retrogradation of Truth

According to the principle of retrogradation of truth (RGT), if p is true\r\ntoday, then it was true in the past that p would be true today. While\r\nthis principle is trivially true in deterministic temporal semantics, it is\r\nsurprisingly not validated in many indeterministic temporal semantics.\r\nYet, it is a very intuitive principle, and such intuitiveness has also been\r\nrecognized by many open futurists. However, its validity is usually acknowledged only at a post-semantic level. In this paper, we present a\r\nsemantic system that validates the principle of retrogradation of truth.\r\nThis system has two indices: one representing the evaluation moment and another representing the moment at which the world has arrived.