Necessary Thing

[Ignorant]

We seem to be talking entirely at cross purposes.

I'm saying we have an observable set of objects A. Let set B be the unobservable ones.

B might be empty, but we can't assume it is.

Objects in set A may be contingent on objects in group B.

If they are, we have no way to examine this relationship whatsoever. A case as simple as B containing two objects, both contingent on each other, and everything in set A being contingent on one of them, is enough to produce a result where nothing is non-contingent.

We can't simply say "so and so is impossible within group B because of a parallel with group A".

Thanks for clarifying!

1) The example you provide is not an infinity of conditions. Rather it is a circular one composed of a finite set.
2) Mutual contingency is not actually contingency. 

Consider the hypothetical thing X which exists on the condition that Y exists, which is to say Y's existence is more fundamental than X => If X exists, it presupposes the existence of Y. If Y exists, it does not presuppose the existence of X, but merely provides the conditions necessary for X. X means Y also. Y means just Y (and any of its own conditions).

Now consider mutual dependence. X exists on the condition that Y exists. If X exists, it presupposes Y also. However, Y exists on the condition that X exists. In other words, if X exists, it presupposes Y AND X also! Because the conditions of the conditions belong to the conditions of the thing itself, mutual contingency is really just non-contingency. Y(X) <= X(Y) <= Y(X). Pretty sure that just means that X = Y.