In assessing the question as to whether or not God exists, I believe that from whichever perspective we are coming from (atheism, theism, etc.) it is important to approach the question carefully and properly. For instance, if God does exist, how would I come to know that? Certain Philosophers and theologians alike have argued that reason cannot judge the answer to that question, and that we rather must take it as a matter of faith . William James for instance in his paper entitled The Will to Believe (1896), takes the view that it is the sincerity and absolute certainty he carries with his faith that precedes the “logical spirit.” He writes:
I have long defended to my own students the lawfulness of voluntarily adopted faith; but as soon as they have got well imbued with the logical spirit, they have as a rule refused to admit my contention to be lawful philosophically, even though in point of fact they were personally all the time clock-full of some faith or other themselves. I am all the while, however, so profoundly convinced that my own position is correct, that your invitation has seemed to me a good occasion to make my statements more clear. 
Thence, it is perhaps entirely proper to ask as to whether or not God’s existence can be known at all. Furthermore, it is probably just as important as to inquire into the nature of what an argument for God’s existence might look like. What sorts of evidences do these arguments use in order to gather their strength? In the former half of this post I simply wish to address the approach of our subject, rather than the perspectives that might answer the question (does God exist?) affirmatively, negatively, or possibly with ignorance.
God’s Existence and the Role of Reason
When addressing the discussion of “What reasons can be given to establish the existence of God?”, some philosophers believe that we have already gone wrong in thinking that such a discussion could take place. Nicholas Everitt (2003) distinguishes between three group of thinkers who believe that reason does not play a role in the establishment (or dis-establishment) of God’s existence :
- (1) It is blasphemous or impious (or at least superfluous) to appeal to reason.
- (2) It is not impious, but it is pointless because there are no reasons to be given.
- (3) Reason is possible, but they are inconclusive and cannot settle the question.
In respect to these given camps, I sometimes find lay-man who are not familiar with this subject either completely surprised that Christians would leave little room for reason in respect to their religious beliefs, or others who just shrug their shoulders and express a few comments of “not surprised.” It is the former to which I tend to side with. However, it is indeed true that such believers have thought this way. One notable figure that often gathers much attention is the early church father Tertullian (AD 160-220) who once wrote in harsh hostility toward the intrusion of philosophy into theology. As he writes in his de praescriptione haereticorum (“On the Rule of the Heretics”):
For philosophy provides the material of worldly wisdom, in boldly asserting itself to be the interpreter of the divine nature and dispensation. The heresies themselves receive their weapons from philosophy. . . What is there in common between Athens and Jerusalem? between the Academy and the church? Our system of beliefs comes from the Porch of Solomon, who himself taught that it was necessary to seek God in the simplicity of the heart. . . We have no need for curiosity after Jesus Christ, nor for inquiry after the gospel. 
Tertullian elsewhere has made the infamous statement that “the Son of God died; it is by all means to be believed, because it is absurd. And He was buried and rose again, the fact is certain because it is impossible” . This statement from Tertullian – “I believe because it is absurd” (credo quia absurdum) – has been one of much controversy. It is interesting to hear from Sigmund Freud (himself an atheist) and his response to Tertullian’s Credo: “[T]his Credo is only of interest as a self-confession. As an authoritative statement it has no binding force. Am I to be obliged to believe every absurdity? And if not, why this one in particular? There is no appeal to a court above that of reason” .
Considering Paul’s sermon on Mars Hill (cf. Acts 17) given to the Greek philosophers – Stoics, Epicureans and some Neo-Platonists – John Mark Reynolds gives an interesting vivid expression of the scene:
Paul. . . points out that the true God cannot live in any temple made by humans and that no human could ever serve him. This was an obvious philosophical truth. If there is a God, then no temple can hold him. He also creates all things and provides a basis of unity for all who are his children. Paul is establishing points of agreement between his gospel and some of the philosophies of the Greco-Roman world. There is nothing in the sermon thus far that would have offended or even educated a good Neo-Platonist or Stoic. 
The point to be made is particularly that Paul is drawing similarities and comparisons between his Christian worldview and Greek philosophy – for instance, he goes so far as to quote the Stoic poet Aratus, who says that humans are the “offspring” of God (cf. v. 28). Thus, even the apostle Paul, who his quoting pagan literature, might see some form of legitimate vocation for the Christian’s usage of philosophy towards the aid of his theology/apologetic. As Reynolds further states, “Without the aid of divine revelation, [philosophy] must remain incomplete and blind. Since humans cannot command revelation to come from the gods, this search was the best humanity could do” .
The role of reason and its relationship to the role of revelation has been expressed in a spirit of companionship stemming back church fathers such as Justin Martyr and Clement of Alexandria in the first century, to even St. Augustine in the fourth and St. Thomas Aquinas in the thirteenth. To provide a given quote from each:
- Justin Martyr: “Whatever all people have said well belongs to us Christians. For we worship and love, next to God, the Logos, who comes from the unbegotten and ineffable God. . .” (Justin, Apology: 148-61)
- Clement of Alexandria: “it might be that philosophy was given to the Greeks immediately and indirectly, until such time as the Lord should also call the Greeks. For philosophy acted as a “custodian” to bring the Greeks to Christ, just as the law brought the Hebrews. True philosophy was by way of a preparation, which prepared the way for its perfection in Christ.” (Clement, Stromata)
- St. Augustine: “If those who are called philosophers, particularly the Platonists, have said anything which is true and consistent with our faith, we must not reject it, but claim it for our own use, in the knowledge that they possess it unlawfully.” (Augustine, de doctrine Christiana)
The point to be made then is that reason is not in contrast to revelation. To use Clement’s language, reason has been understood to act as a “custodian” to bring those to Christ, so that “true philosophy was by way of a preparation, which prepared the way for its perfection in Christ.”
God’s Existence and our Knowledge – II
In the previous section, we looked at the idea regarding reason and its complementary role with revelation/faith. However, in this section I wish to deal with the dilemma regarding the issue of whether or not we can know if God exists. Otherwise stated, in respect to some hard forms of agnosticism we cannot know if God exists. This issue has been associated with the thought of German philosopher Immanuel Kant (1724-1804).
Kant himself believed that God existed, but he nonetheless felt that no one could know as to whether or not he existed. Two basic reasons for suggesting this to be the case are present:
- (1) There is an appearance/reality disjunction.
- (2) Contradictions emerge once you suggest that categories of the mind apply to reality.
Kant argued that object’s in and of themselves cannot be known, but rather only objects as-it-appears-to-me are known. In other words, everything that we know or come to know is through our senses (a.k.a, a posteriori), but is formed and categorized by the categories of the understanding. As Norman Geisler (1980) explains,
According to Kant, all knowledge begins with experience, but there is no knowledge without the contributions of the mind itself. Kant claimed that the mind contributes the “forms of sensibility,” space and time, which are necessary for understanding experience. All of our intuitions (perceptions) occur within the limits of time and space, which are the forms by which experiences is organized. 
Given this account, there are three sciences (according to Kant) which are now no longer possible since they are sciences beyond all possible experience: (1) An empirical cosmology (a science of the real world), (2) an empirical psychology (a science of a real “self”) and (3) a rational theology. Thus, this unknowability of things-in-themselves not only apply to objects, but to God as well.
The criticism of this view can however been seen from Paul’s statements in Romans where he says: “What may be known of God is manifest in them, for God has shown it to them. For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead” (Rom. 1:19-20). In other words, God is known only through his effects, or in respect to his relation to the created order. This is due in large part to his “ontological precedence” (to borrow a term from Diogenes Allen, 1985) to the universe.
Thus, on this grounds I do not think that one could side with Kant when they are suggesting that we cannot know whether or not God exists. Furthermore, if the objection were taken to be more general, thus to say “We cannot know infinite reality but we can know finite reality” commits nearly the same errors as Kant. To borrow Geisler’s (1980) criticism:
[T]he very denial of knowledge of an infinite implies some knowledge of the infinite. One must know what cannot be denied of God if he knows what can be denied of God. Further, when one says “I cannot know the Infinite,” another may justly ask, “You cannot know what?” If the agnostic does not have some knowledge of the infinite, then the very denial is meaningless, since he cannot know even the meaning of the term infinite in his denial. 
Some Things Understood
First, might we be right in addressing what proofs of God’s existence typically look like? In this section I wish to deal in brief what is meant by a “proof” of God’s existence and the structure of some arguments that demonstrate God’s existence. First, as Oxford philosopher Anthony Kenny (2004) points out, “All such proofs [of God’s existence] start from a phenomenon, or class of phenomena, within the world, which demand explanation. They go on to show a particular type of explanation will not lead to intellectual satisfaction, however frequently it is applied” .
Furthermore, Kenny notably states:
Proofs of the existence of the God, if they are not to be mere appeals to ignorance and incomprehension, must not depend on particular features of the world which yet are unexplained. The appeal to God is not based on particular failures of explanation but upon the provable inability of a particular pattern of explanation to give an intellectually satisfying understanding of phenomena of a certain type. 
If it is unclear now, the application of Kenny’s clarification of “proofs” will be seen throughout the remainder of this post. When we do examine certain philosophers and their arguments, we will notice particularly that they focus on some given thing in order to stipulate that God is the best explanation for that given thing. For instance, complexities in nature might point to an intelligent Designer, and a universal moral law that holds true for all people everywhere at all times might point us to a Moral Law Giver. However, this and more will be explored much later.
Arguments then, can be separated in two forms:
- (1) A priori arguments
- (2) A posteriori arguments
(1) denotes only one specific kind of argument, and (2) is a family of arguments. By (1) I simply mean arguments that are based independently of experience and by (2) I mean arguments that are based on experience. Only one argument has ever been made to be known apart from experience and that is the Ontological Argument as formed by St. Anselm of Canterbury in the 11th century – among Descartes, Spinoza, Leibniz and others. The Ontological Argument is an a priori argument because it demands an explanation of the phenomenon regarding our conception of God. God, as defined by Anselm, is the greatest conceivable being, or a being by which none greater can be conceived. Anselm argues that we understand what we hear when he hear this definition (even the atheist), and thus, this being must exist not only in our minds, but also in reality. This argument will be examined later.
Other such arguments, or a posteriori arguments, are arguments that look to some given fact about the world within our realm of experience and demand some given explanation of its existence. One argument is as follows:
- Every being (that exists or ever did exist) is either a dependent being or a self-existent being.
- Not every being can be a dependent being.
- Therefore, there exists a self-existent being.
The conclusion (3) would be the implicit stating of God’s existence – since, according to (2), not everything can be a dependent being. This argument is what is known as the Cosmological Argument, and will be examined in greater detail throughout the remainder of the post. It is surely one of the more popular arguments in contemporary discussions within the philosophy of religion, and so will be treated with some care and genuine scrutiny.
The task of this post is to appeal mainly to the atheist, particularly one who believes that there are no arguments for God’s existence or that there are no reasonable arguments to establish this existence. I think there are good, reasonable and intellectually viable reasons for believing in God’s existence, most notably seen from the realm of philosophy and science. I think that this clarification discussion was important in order to understand the structure of the next part – namely, the arguments themselves. Of course, this was by no means meant to be exhaustive nor even scholarly so as to asses the wave of literature and discussion on this material, but rather definitional so as to prepare the atheist for a coherent framework of understanding the structure of discussing God’s existence.
-  Blaise Pascal (1623-1662) makes the notable comment that “by faith we know [God’s] existence, through glory we shall know his nature.”
-  Quoted from Reason and Responsibility, ed. Joel Feinberg and Russ Shafer-Landau (Thomson and Wadsworth: 2005) p. 102
-  Nicholas Everitt, The Non-Existence of God (Routledge: 2003) p. 2
-  Quoted from Alister McGrath, The Christian Theology Reader, 2nd edn. (Blackwell Publishers: 2001) pp. 7-8
-  Quoted from George H. Smith, Atheism: The Case Against God (Promotheus Books: 1979) p. 99
-  Sigmund Freud, “The Future of an Illusion”, quoted from Critiques of God, ed. Peter Angeles (Promotheus Books: 1997) pp. 151-152
-  John Mark Reynolds, When Athens Met Jerusalem (IVP Academic: 2009) p. 242
-  Ibid., p. 248
-  Norman Geisler and Paul Feinberg, Introduction to Philosophy (Baker Books: 1980) pp. 88-89
-  Ibid., p. 299
-  Anthony Kenny, The Unknown God (Continuum Press: 2004)
-  Ibid. – emphasis mine.