What's Metaphysically Necessary?

My favourite theory of what's metaphysically necessary is that every possible world shares some initial part with the actual world. It doesn't follow that there's any particular atomic element item that's necessary. The necessity just attaches to there being a regress. If we don't go infinite regress for the causal items, then i think we're just going to suppose there's the first causal item,. and then the quest that will arise is: K, so is it necessary, or is it contingent rigt gae? Those will be the two options. O ka, say so say on the so infinite regress of one possibility, say, one option, and you can go bruet contingency or brute