There are several arguments for the existence and non-existence of god; these comprise of the Ontological arguments, the Cosmological arguments, the Teleological arguments and the Moral arguments. The leading argument against the existence of God concerns the problem of evil.
The Danish philosopher Soren Kierkegard (1813-1855) argued that it is inappropriate to establish a belief in God based on reason, and instead emphasized faith. However, despite his skepticism about the value of reason in supporting a belief in God, many philosophers have tried to prove the existence of God by rational argument.
The Ontological argument proceeds from the assumption that we can talk rationally and with meaning about God; and with an analysis of the significance of the concept of God, we can conclude with the existence of God. The most famous Ontological argument was derived from St Anselm of Bec(1033-1109),in his book 'The Proslogion'. This argument upholds the God interpreted as the greatest being that can be conceived, must exist, since a being that does not exist would by the merit of that fact lack a quality that contributes to it's greatness. The very notion of a being, than which nothing greater or more pure can be conceived, entails its presence, for existence is itself an aspect of perfection.
St Anselm's argument goes as follows:
1-Consider the idea of God. God is a being that is absolutely perfect, a being that cannot be surpassed in greatness.
2-The greatest conceivable being cannot simply exist contingently,for there is a greater being that would have necessary existence.
3-As God is the greatest conceivable being then he must have necessary existence.
4-A logically necessary being is one whose non-existence is inconceivable.
5-Therefore, if God has necessary existence then God's non-existence is inconceivable.
6-Therefore, God must exist.
Criticism for this argument rests in two main areas, firstly- whether existence actually contributes to a beings greatness.And secondly on the fact that this argument relies on the idea of God,which mortals can not be sure of. This view was the reason why St Thomas Aquinas (1225-1274)rejected the argument.
The second group of important arguments for God's existence is the Cosmological argument, of which there are many. The prime result of the Cosmological arguments is that they provide us with a ways of explaining the universe, of understanding the universe and its origins. The simplest of these arguments is derived from two Arab philosophers called al-Kindi (c.870) and al-Ghazali (1058-1111); the argument is called the Kalam argument:
1- Everything that begins to exist has a cause for its existence.
2-The universe began to exist.
3-Therefore, the universe has a cause for its existence.
However, the most famous cosmological arguments came from St Thomas Aquinas, these are:
1- From motion. Things move, they don't move themselves, their movers don't move themselves, this series of movers cannot be infinite, therefore there must be a first unmoved mover, whom we call God.
2-From causation. Most things are effects, their causes are in turn effects, the cause/effect series cannot be infinite, therefore their must be a first uncaused cause, whom we call God.
3-From contingent realities. Contingent beings need to be explained (as to where they came from), their explainers need in turn to be explained, this explanatory series cannot be infinite, therefore there must be an unexplained explanation, whom we call God.
The philosopher, Immanuel Kant(1724-1804)rejected these Cosmological arguments, but formed his own version, as follows:
1-Something exits (e.g a tree).
2-This thing came from a series of other causes (e.g from seeds that in turn come from other trees).
3-This network is a part of a greater network: the cosmos that in turn is a contingent totality.
4-It is inconceivable that the universe might not have existed.
5-Thus, the universe which does exist, needs an explanation.
6-Yet the universe is greater than the individual cause and effect chains which make it up.
7-Therefore, there must be something beyond the physical and contingent universe to which reference must be made.
It has been claimed that these arguments are flawed in the sense that the existence of the universe might be an irrational fact without explanation. Also, supplying the existence of a necessary being who created the universe, is not the same as proving the existence of God. A necessary being might lack the qualities fundamental to God, such as being all good.
The Teleological argument relies on the idea that the universe is comparable to a machine, and therefore must have had a designer, whom we call God. William Paley, an 18th century theologian, was the best known promoter of this view, however, David Hume (1711-1776) contested that this analogy was weak, and that the universe can just as strongly be compared to a living organism, in which case it would have been created by reproduction, not design.
Immanuel Kant's Moral argument states that mankind should strive to reach the highest good including moral virtue, with happiness being the reward. He saw this a humanities duty and it is therefore possible to realize it. However, this cannot be realized unless there is a' supreme cause of nature', such a cause can only be God.
The 17th century philosopher, Blaise Pascal (1623-1662), also formed an argument for God's existence, known as Pascal's wager. This view proposed that even if reason cannot confirm God's existence, it is still advantageous to believe in God. This is due to the belief in God being a better wager than non-belief, because there are infinite rewards to gain and little to lose by believing versus infinite rewards to lose and little to gain by not believing. However, if Pascal's wager is to be one's sole reason for one's belief in God, then surely the entire concept of moral virtue is missing and is instead replaced by vice.
The Problem of Evil is the best argument for God's non-existence. J.L.Mackie explains the concept by calling it an inconsistent triad:
1-God is all Powerful.
2-God is all Good
3-Evil exists.
He claims one of the statements must be removed or contradicted, if there is to be any sense made.'God is all knowing (omniscient), all powerful (omnipotent),morally perfect and all loving. Such a God would not allow evil to occur, but evil does occur. If what is God is omniscient and omnipotent then God must know about evil and must know how to prevent all evil, and be able to act upon this. An all loving God must wish to prevent all evil, therefore there is no God'.
In conclusion, all these arguments, either for or against God's existence are convincing, and yet neither are the undisputed truth. This can surely only be a deliberate act of God, due to the fact that if the existence of God could be proven, then mankind would be forced to believe and therefore believe out of vice. As opposed to the Christian ideal of mankind having undisputed faith in God's existence, and consequently living a good life out of one's own virtue.