Over recent months I have become more and more interested in literature regarding the justifications for atheism. Though I have been buying books of these sort for some time, I’m interested to see how a particular philosopher will begin before he sets up his arguments against theism. As of recently I have seen a strange trend among unbelievers regarding the definition of atheism and what it means to “deny” the existence of God. Let’s look at a few examples.
Ernest Nagel was the university emeritus professor of philosophy at Columbia University and served as editor for numerous journals such as the Journal of Philosophy (1938-56), the Journal of Symbolic Logic (1940-46), and the Philosophy of Science (1956-59). One work in particular that I’m interested in examining is his paper entitled Philosophical Concepts of Atheism (1959) in which he understood atheism as the following:
I shall understand by “atheism” a critique and a denial of the major claims of all varieties of theism… not to be identified with sheer unbelief, or with disbelief in some particular creed of a religious group. Thus, a child who has received no religious instruction and has never heard about God, is not an atheist – for he is not denying any theistic claims. 
However, in direct contrast, atheist George Smith in his book Atheism: The Case Against God (1979) offers a completely different perspective on the meaning of atheism:
Atheism… is the absence of theistic belief. One who does not believe in the existence of a god or supernatural being is properly designated as an atheist… Atheism, in its basic form, is not a belief: it is the absence of belief. 
However, Smith goes on later to state that “it is the atheist who demands proof from the theist, not vice-versa” . His reasoning for this is because the burden of proof ‘‘falls on the person who affirms the truth of a proposition, such as ‘God exists.’ If the theist claims to know that God exists, then we have the cognitive right – indeed, the responsibility – to ask this person how he acquired this knowledge and why we should take him seriously” . Therefore, we can avoid the dilemma that I wish to explore.
Always an interesting problem presented to atheism has been the assertion that they are not humble in their claims to knowledge. Of course, if we are sticking to Nagel’s supposed “explicit” definition  of atheism, then the atheist cannot justify what he tries to establish. Annie Besant in her essay Why I Do Not Believe in God (1887) rightly points out:
For be it remembered that the Atheist makes no general denial of the existence of God; he does not say, “There is no God”… the proof of a universal negative requires the possession of a perfect knowledge of the universe of discourse, and in this case the universe of discourse is conterminous with the totality of existence. No man can rationally affirm “There is no God”, until the word “God” has for him a definite meaning, and until everything that exists is known to him, and known with what Leibniz calls “perfect knowledge” .
The significance of this passage (as I think she is right) is that atheism cannot justify a universal claim such as “There is no God”, for that would assume that the atheist throughout the totality of existence has “perfect knowledge” (indeed, God-like knowledge) that there is no God. Smith even recognizes this in his book when he says that “No one can lay claim to omniscience, but this is precisely what the atheist supposedly does when he says that God does not exist” .
In order to avoid the problem, Smith responds that
The short and easy refutation achieves its victory by attacking a counterfeit form of atheism that has rarely been advocated by real atheists… Nineteenth-century atheists repeatedly attacked the short and easy refutation by exposing its faulty definition of atheism (known as positive atheism, since it positively affirms the nonexistence of God).
Charles Bradlaugh, the late nineteenth-century British freethinker even in his essay A Plea for Atheism (1864) subscribes to Smith’s view of atheism when he wrote that the “Atheist does not say ‘There is no God’, but he says: ‘I know not what you mean by God; I am without idea of God; the word ‘God’ is to me a sound conveying no clear or distinct affirmation” .
Theism and Humble Claims to Knowledge
Famous magician Penn Jillette in his new book, God, No! Signs You May Already Be an Atheist and Other Magical Tales (2011) has regarded theists as ‘arrogant’ for claiming to have insight into the question regarding God’s existence . He even goes on to say that “what I’m claiming is not in any way arrogant. It couldn’t be more humble. It’s just ‘I don’t know'” (xvi). However, I would have to side with Besant on this issue, that given Nagel’s definition of atheism (which has been the historical definition), atheism does not present itself as some kind of ‘agnostic ignorance’ like that found in Penn Jillette’s book.
All theism claims to hold, is the possibility of somewhere in the totality of existence a being that is recognized and believed to be God, exists. This is a much more humble claim than what atheism holds.
-  quoted from Critiques of God, ed. Peter Angeles (Promotheus Books: 1997) p. 4
-  George Smith, Atheism: The Case Against God (Promotheus Books: 1979) p. 7
-  Ibid., p. 27
-  George Smith, Why Atheism? (Promotheus Books: 2001) p. 31
-  see Smith (1979), p. 13
-  quoted from Gordon Stein, An Anthology of Atheism and Rationalism (Promotheus Books: 1980) p. 31
-  Smith (2001), p. 22
-  Gordon Stein (1980), p. 10
-  Penn Jillette, God, No! (Simon&Schuster Publishing: 2011) xvi.