1. Something exists.
2. Whatever exists does so either because it exists eternally or because it's existence is dependent upon some prior cause or set of circumstances.
3.If all things that exist are dependent for their existnece there is no actual explanation of causes
4. Therefore, there exists at least one eternal thing
5. The one eternal thing is the logical explanation for all causally dependent things
6.Any eternally existing cause of all things is worthy of the appellation "God."
7. Therefore God exists.
There are different types of necessity and contingency,
Truth itself can be either necessary or contingent:
Distinction between kinds of truth. Necessary truth is a feature of any statement that it would be contradictory to deny. (Contradictions themselves are necessarily false.) Contingent truths (or falsehoods) happen to be true (or false), but might have been otherwise. Thus, for example: "Squares have four sides." is necessary. "Stop signs are hexagonal." is contingent. "Pentagons are round." is contradictory. This distinction was traditionally associated (before Kant and Kripke) with the distinctions between a priori and a posteriori knowledge and the distinction between analytic and synthetic judgment. Necessity may also be defined de dicto in terms of the formal logical property of tautology. Recommended Reading: Jules Vuillemin, Necessity or Contingency? (C S L I, 1995); Colin McGinn, Logical Properties (Oxford, 2001); Alvin Plantinga, The Nature of Necessity (Clarendon, 1989); and Margaret Dauler Wilson, Leibniz' Doctrine of Necessary Truth (Harvard, 1984).
There are many different notions of necessity. There are different kinds of necessity they are not contradictions or different opinions they apply in different ways, For example logical necessity is not the same as metaphysical necessity, metaphysical or broadly logical necessity deals with the nature of existence.
...Something is “necessary” if it could not possibly have failed to exist. The laws of mathematics are often thought to be necessary. It is plausible to say that mathematical truths such as two and two making four hold irrespective of the way that the world is. Even if the world were radically different, it seems, two and two would still make four. God, too, is often thought to be a necessary being, i.e. a being that logically could not have failed to exist.
Something is “contingent” if it is not necessary, i.e. if it could have failed to exist. Most things seem to exist contingently. All of the human artefacts around us might not have existed; for each one of them, whoever made it might have decided not to do so. Their existence, therefore, is contingent. You and I, too, might not have existed; our respective parents might never have met, or might have decided not to have children, or might have decided to have children at a different time. Our existence, therefore, is contingent. Even the world around us seems to be contingent; the universe might have developed in such a way that none of the observable stars and planets existed at all.This is true in the cosmological argument.
The modal cosmological argument or “argument from contingency” is the argument from the contingency of the world or universe to the existence of God. The argument from contingency is the most prominent form of cosmological argument historically. The classical statements of the cosmological argument in the works of Plato, of Aquinas, and of Leibniz are generally statements of the modal form of the argument.The Universe itself is contingent and everything produced in nature is as well.
Karl Popper tells us :"Empirical facts are facts which might not have been. Everything that belongs to space time is a contingent truth because it could have been otherwise, it is dependent upon the existence of something else for its' existence going all the way back to the Big Bang, which is itself contingent upon something." Contingent beings are those whose existence is caused or explained, "A contingent being (a being such that if it exists, it could have not-existed or could cease to exist) exists. This contingent being has a cause of or explanation for its existence. ... Therefore, what causes or explains the existence of this contingent being must include a non-contingent (necessary) being".
Necessity/contingency broadly logical and causally related
This seems to create a dichotomy for some atheists in that they try to juxtapose two kinds of contingency against one another; There are Types of necessity and contingency but the distinction between broadly logical or "Metaphysical" necessity and the causal type reflected in my CA is not one of them, These two types were shown by Hartshorne to be united,. The causal form of contingency is a marker for the broadly logical or metaphysical. This is my own idea.
Necessity is that which cannot cease or fail to exist; that for which one could contradict to speak of such things. Thus contingency is that which can cease or fail to exist.But it seems that ceasing and failing are bound up with causes and circumstances of existence in the natural world, Thus we can think of causality an an ontological marker spellimg out for us the nature of contingency in the natural world,. After all anything that depends for its existence upon a prior condition (even an ontologically prior condition that is not temporally prior) is contingent because it could cease or fail to exist, thus its contingency is marked by its causality.
Garth Kemerling,"Necessary/Contingent," Philosophical Pages. 1997/2011
http://www.philosophypages.com/dy/n.htm#nec (accessed 3/4/19 )
Matthew Davidson,"God and Other Necessary Beings", The Stanford Encyclopedia of Philosophy (Spring 2015 Edition), Edward N. Zalta (ed.), <https://plato.stanford.edu/archives/spr2015/entries/god-necessary-being/>. (accessed 3/4/19 )
 Tim Holt, "Argument from Contingency," Philosophy of Religion, 2008
(accessed 3/4/19 )
 Carol Popper quoted in Antony Flew, Philosophical Dictionary, New York: St. Martin's Press, 1979, 242.
 Bruce Reichenbach, , "Cosmological Argument", The Stanford Encyclopedia of Philosophy(Spring 2019 Edition), Edward N. Zalta (ed.), forthcoming URL = <https://plato.stanford.edu/archives/spr2019/entries/cosmological-argument/>.
(accessed 3/4/19 )
B Reichenbach originally Jul 13, 2004