  Defenders of the proportional syllogism (McGrew 2003; Campbell and Franklin 2004) argue that no assumption of randomness is needed. Any information about bias would indeed change the probability, but that is a trivial fact about any argument. An argument infers from given premises to a given conclusion; a different argument, with a different force, moves from some other (additional) premises to that conclusion. Given just that the vast majority of airline flights land safely, I can have rational confidence that my flight will land safely, even though there are any number of other possible premises (such as that I have just seen the wheels fall off) that would change the probability if I added them to the argument. The fact that the probability of the conclusion on other evidence would be different is no reason to change the probability assessment on the given evidence.