 A-theorists and B-theorists appeal to different sources of evidence for their different views of passage. A-theorists typically emphasize how psychologically we seem to perceive a world of robust passage or “flow” of time. In physics, the laws of thermodynamics seem to imply a strong past-to-future direction to time. And quantum mechanics seems to identify an important sense of simultaneity, which could be identified with presentness (see  section 11  below). Finally many commonsense ways of thinking of change seem to rely on A-theory descriptions of passage. For instance, they will use the fact that we care so much about whether bad events are past as evidence that there are ineliminable tensed propositions and those propositions represent ineliminable A-properties.