A: I've this model in which there's a cosmological time t takes only positive values.
B: Doesn't that contradict causality? I mean, every event should be preceded by a cause.
A: Well, the state of the universe at every t has a prior state that determines it, which is as strong a sense of "cause" as it gets.
B: But what about t≤0? What happens then?
A: That makes no sense in this model; the entire universe has t>0. That's all there is.
B: I still think there's a contradiction. I like the idea of t in (-inf,inf) better, since it avoids it. Your model has nothing before t = 0; this one does!
A: What are you talking about? The model satisfies causality as you defined it. If you've some version of causality in mind, what is it?
I suppose it could be formalized thus: Not only every individual event has a cause that precedes it, but also every set of events, provided they all lie within a finite time interval.