Aristotle outlines very complex and complicated constraints on his syllogistic reasoning. I don’t know the full implications or principles of it, but it seems that what is contingent cannot be converted; yet with what is particularly necessary, its opposing contrary of opposition and ontology is naturally assumed. It also seems that the further down this abstraction of contingency that we go, the less certain we can be of any refutation, or demonstration. It seems to be a presupposition, that what was in 2nd figure, in order to demonstrate, or refute, necessitates that a premise can be converted back to 1st figure syllogisms. This, however, is where problems begin, and the doors begin to close logically, especially for categoric contingent premises. Thus, the only certainty that we seem to have in this 2nd figure, is what something is not at present, and universally what that very thing is not now, was not, and never will be. Understanding the certainty of privation seems to be key to mastering the rules of modal syllogisms in 2nd figure.
EAR