The following modal cosmological argument goes back to John Duns Scotus.
(Premise) Possibly, there is an object that cannot have a cause,
(Premise) Every contingent object, possibly, has a cause,
(Conclusion) There is a necessary object.
The logical derivation is quite straightforward. According to the first premise there is a possible world that contains an object, let us say A, that is uncaused in every possible world in which it obtains. Now, due to the second premise, object A cannot be a contingent object. Therefore, object A is a necessary object.
Both premises seem to be plausible. Yet, together they entail an very interesting metaphysical conclusion, that is, the conclusion that there is something in the actual world that exists necessarily.