Abstract
Presentism is the thesis that only the present exists, and that the past and future are nothing. One of its motivations is to account for the passage of time, which it makes consist of an ontological flow: to become present is to enter existence, while to become past is to leave it. I would argue that presentism cannot actually live up to its brief, because it stumbles over what I call the problem of the ready-made past. A world with a ready-made past is a double of our own as it is now, with the difference that it only begins to exist now; it therefore has no past behind it, even though it contains all the entities that, according to presentists, represent a past in the present: tensed properties, haecceities and so on. I will attempt to show that presentist ontology does not have the resources to explain what distinguishes this world from ours, and thus to tell us what the passage of time consists in.
