This is a sore point for me as I've had trouble with atheists on this point lo these many years of internet apologetics. Over this last week end I had an argument with three atheists at once over the Cosmological argument (comment section of this blog). My argument asserts that all natural things are contingent because they require causes, At least we have no examples of things that don't require causes,
IMS (I am Skeptic): " I do not accept this. Contingent things (if defined as things whose existence has a beginning in time) have a cause (by premise 1), but that cause could be anything. I do not grant that it must be a necessary thing."
Meta*: this is a deductive argument man. We are going to deduce something we do that by arguing premises, p2 doesn't to embody the conclusion of the argument it only has to be true in itself, saying it could be anything is BS because by the end of the argument it will be apparent not true.
*for those who don't know I am Meta (aka Metacrock) ,my old screen name
Rather than sufficient I used contingent but the word has a causal dimension it is not a misue of the term. In the quotation abovevthe relivant part is:
In causal relations, a necessary condition for the occurence of an event is a state of affairs without which the event cannot happen, while a sufficient condition is a state of affairs that guarantees that it will happen. Thus, for example: the presence of oxygen is a necessary condition for combustion, and the flow of electrical current is a sufficient condition for the induction of a magnetic field. Recommended Reading: Brian McLaughlin, On the Logic of Ordinary Conditionals (SUNY, 1990); Conditionals, ed. by Michael Woods, David Wiggins, and Dorothy Edgington
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.
The argument from contingency rests on the claim that the universe, as a whole, is contingent. It is not only the case, the argument suggests, that each of the things around is us contingent; it is also the case that the whole, all of those things taken together, is contingent. It might have been the case that nothing existed at all. The state of affairs in which nothing existed at all is a logically possible state of affairs, even though it is not the actual state of affairs.
I have made the argument in causal terms and I chose to use the e\term "contingent," I could tweak the argument and use another term, I may do that, it doesn't matter. IMS has nothing to say so he refuses to accept the definition but the truth is her can't me a single example of some aspect of nature that doesn't have a cause. We trace those causes to the big bang and can trace o further but we have no proof of what caused the big bang.
Moreover I will make a sub argument here to the effect that materialism itself depends upon accepting the notion that all natural things have causes.
Dictonary of Philosphy Anthony Flew, article on "Materialism" Backing up Flew's assumption is Christepherv Southgate"
"...the belief that everything that exists is ethier matter or entirely dependent upon matter for its existence."
"...Beyond the Christian community there was even greater unease. One of the fundamental assumptions of modern science is that every physical event can be sufficiently explained solely in terms of preceding physical causes. Quite apart from its possible status as the moment of creation, the Big Bang singularity is an offence to this basic assumption. Thus some philosophers of science have opposed the very idea of the Big Bang as irrational and untestable." 
The great philosopher Alfred North Whitehead, also mathematician who wrote Principia Mathematica with Bergrand Russell, stated:
"We are content with superficial orderings form diverse arbitrary starting points. ... sciene which is employed in their deveopment [modern thought] is based upon a philosophy which asserts that physical casation is supreme, and which disjoins the physical cause from the final end. It is not popular to dwell upon the absolute contradiction here involved."[Whitehead was an atheist] 
It was La Plase's famous line "I have no need of that Hypothesis" [meaning God] Which turned the scientific world form believing (along with Newton and assuming that order in nature proved design) to unbelief on the principle that we don't' need God to explain the universe because we have independent naturalistic cause and effect. [Numbers, God and Nature] 
We still have a huge justification for assuming causes inductively, since nothing in our experince is ever uncaused. The mere fact that we can't see or find a cause isn't a proof that there isn't one.
Thus, the basis upon which God was dismissed from scientific thought has been abandoned;the door to consideration of God is open again. The reliance upon naturalistic cause and effect in consideration of ultimate origins is shattered, but this does not make it rational to just assume that the universe opoped into existence with no cause. Since we have vast precident for assuming cause and effect, we should continue to do so. But since naturalistic cause and effect seems unnecessary at the cosmic level, we should consider the probablity of an ultimate necessary final cause.
 Garth Kemerling, The Philosophy Pages (websiter are licensed under a Creative Commons Attribution-ShareAlike 3.0 ) URL:
This is a concise guide to technical terms and personal names often encountered in the study of philosophy. What you will find here naturally reflects my own philosophical interests and convictions, but everything is meant to be clear, accurate, and fair, a reliable source of information on Western philosophy for a broad audience. The curriculum vitae elsewhere on this site describes my experience in academic life.
Garth Kemerling Ph.D. In Philosophy from University of Iowa
 Tim Holt, "Philoso[hy of Reliogion," www.philosophyofreligion.info website. URL:
rom one of his sites: Tim has Bachelor's and Master's degrees in philosophy from the University of Sheffield, and a Diploma in Theology from the University of Oxford. From September 2005, he has been teaching philosophy, religious studies, and critical thinking at Cirencester College.
 Anthony Flew, "Materialism," Dictionary of Philosophy, New York: Macmillon press limited, 1979, second revision 1984, 222
 Christopher Southgate and Lawrence Osborn, God, Humanity and the Cosmos. T&T Clark: Edinburgh , 1999 quoted on website:
Center For Theology and the Natural Sciences URL:
http://www.ctns.org/Information/information.html Is the Big Bang a Moment of Creation?(this source is already linked above)
accessed 2001. This site no longer exists. Dr. Sothgate was head of the institute.
this material is now availed on the counter balance website: URL:
 Alfred North Whitehead, Science and The Modern World, .NY: free Press, 1925, 1953. 76
 Roger Hahn, God And Nature: Historical Essays on the Encounter between Christianity and Science. Los Angeles:University of California Press, David C. Lindberg (Editor), Ronald L. Numbers (Editor). 1986, 256-277