You probably have to assume there is a necessary substrate. What else can you possibly think? Contingency means being contingent on something else. You could suppose that the "something else" is itself contingent, but then you have another contingency. At some point you will likely take it for granted that there must be something that is itself not contingent and that the rest of the stuff downstream turns on it being the way it is.
Wait! Contingent was just defined as everything that's not necessary. Not contingent with its normal meaning of dependent on something else. Like, a square has 4 sides, that's necessary for it to be called a square, but it might or might not depend on something else for that quality. Or a square is blue, that's contingent (i.e., what's not necessary in this usage for it to be called a square), and it might or might not depend on something else.
If you are using "contingent" with its normal meaning, the idea is absurd. We can divide everything that exists into "necessary" and "contingent", one or the other? We might as well divide everything into edible and picturesque, for example. Words, but more like word salad than meaningful statements.
> You probably have to assume there is a necessary substrate. What else can you possibly think?
That there's no necessary substrate.
> Contingency means being contingent on something else
Can't it just be "luck", then? Chaos just happened to take this form.
> At some point you will likely take it for granted that there must be something that is itself not contingent
Sorry but I don't agree. I think it is perfectly conceivable that everything is contingent and there's no "necessary substrate". For example: it could be that several factors (things like the gravitational constant and the different fundamental forces) are contingent on isolation, but when they are put together the ensemble becomes necessary. Like in a tensegrity structure (not saying that I think that's what happens to our Universe, just pointing out that there's other options besides "One necessary substrate", and we don't know which one is ours).
Roger Penrose suggests patterns before the "big bang" are observable is my interpretation of what was said between him and Melvin Bragg on a Youtube clip.
I don't see what the infinite sequence of contingency buys you. Seems you might as well say there is fundamentally no reason why anything is (though I think that's untenable).
"What it buys you" suggests that we should assume reality is fundamentally organized for our convenience or comfort, or to avoid being too challenging to our intellectual powers and/or beliefs.
By introducing the concept of reasons into the discussion, you seem to be adding a new dimension of purpose to it (unless you are using 'reason' as a synonym for 'cause', but if so, it would have been clearer to stick with the latter.) Your belief that the universe has a purpose (if that is what you are saying here) does not logically compel anyone else to accept a first cause.
Update: In your view, there is a hierarchy of causes of something, the first of which is necessary and the rest of which are contingent. Therefore, the second cause was contingent. This implies that the first cause made a choice between which of the second-cause options obtained. But as the first cause had a choice, then it could have gone another way, so it was contingent...
