Well, on a somewhat trivial note, I (plan to) make my living proving that certain things have probabilities distinct from 0, so if 0 and 1 weren't probabilities to begin with I'd be out of a job.
That's not really it, though, because I think the "0 and 1 are not probabilities" claim is really about degrees of belief in non-mathematical propositions. In its most-reasonable-to-me form, it says something like "Even if you have an argument that statement S is true with probability 1, you should believe Pr[S] < 1, because your argument could be wrong". And there's... really not a lot I could say in response to that. Except I would note that the value 1 isn't really special here.
But there's a lot of things that go together with this idea that I do disagree with. In very many senses, even non-mathematical propositions do end up having probabilities of 0 or 1. For instance:
Plus in practice accepting "0 and 1 are not probabilities" rhetorically or otherwise just means that you stop writing 1 and start writing 1-epsilon. Whose belief is it really that doesn't affect anything?
even non-mathematical propositions do end up having probabilities of 0 or 1 ... Tautologies
Tautologies are true for mathematical reasons and there is little difference - as far as probability assessment goes - between "P ∨ ∽P" and "Yding Skovhøj is the highest peak of Egypt or Yding Skovhøj is not the highest peak of Egypt". Thus, tautologies (and pseudologies, or how do we call their false counterparts) don't really make a category distinct from mathematical statements.
Conditional probabilities
I am not sure what you mean here. O...
I was very interested in the discussions and opinions that grew out of the last time this was played, but find digging through 800+ comments for a new game to start on the same thread annoying. I also don't want this game ruined by a potential sock puppet (whom ever it may be). So here's a non-sockpuppetiered Irrationality Game, if there's still interest. If there isn't, downvote to oblivion!
The original rules:
Enjoy!