Michael Martin in his book Atheism: A Philosophical Justification (1990) argues for a position known as Negative Atheism and tries to answer the question as to whether or not Positive Atheism is justified. The former position is “the view that one is justified in not believing that there exists an all-powerful, all-knowing, all-good being who created the universe” . In other words, “[u]ntil and unless some such grounds [for claims of knowledge of God] are produced we have literally no reason at all for believing; and in that situation the only reasonable posture must be that of either the negative atheist or the agnostic” . Hence, the negative atheist is one who claims to have no knowledge with respect to the existence of God.
Martin in his book argues that “negative atheism is not justified until it is shown that God talk is cognitively meaningless or, if God talk is cognitively meaningful, that the reasons for believing in God are inadequate” . However, my focus is not so much his treatment of religious language and negative atheism, but rather his argument(s) for positive atheism and the inconsistency within the divine attributes.
Michael Striven in his book Primary Philosophy (1966) argues that a refutation of all the arguments for the existence of God would “establish positive as well as negative atheism” . According to Striven:
[I]f we take arguments for the existence of something to include all the evidence which supports the existence claim to any significant degree, i.e., makes it all probable, then the absence of such evidence means there is no likelihood of the existence of the entity. And this, of course, is a complete justification for the claim that the entity does not exist, provided that the entity is not one which might leave no traces. . . and provided we have comprehensively examined the area where evidence would appear if there were any. 
Hence, if we were to take Scriven’s statement here and turn into a principle of justified belief, Martin maintains that we obtain the following:
- (SP) A person is justified in believing that X does not exist if (1) all the available evidence used to support the view that X exists is shown to be inadequate; and (2) X is the sort of entity that, if X existed, there would be available evidence that would be adequate to support the view that X exists; and (3) the area where evidence would appear, if there were any, has been comprehensively examined.
This what can be known as the Scriven Principle (SP). However, this principle can be faulted for its preoccupation with purely evidential reasons for the justification of belief. Martin recognizes that although “there is a presumption that only epistemic reasons are relevant, this is merely a presumption” . We should perhaps invoke another criterion for this justification of belief (we shall call this new condition (SP’)):
- (4) There are no acceptable beneficial reasons to believe that X exists.
This point is notably important. Martin in this work and in his other book The Case Against Christianity (1991) distinguishes between two kinds of reasons with respect to the justification of belief: (1) Epistemic Reasons and (2) Beneficial Reasons. As Martin writes, “The thesis that without adequate reason one should not believe that an all-good, all-powerful, and all-knowing being exists has been interpreted as a special case of the more general thesis that without adequate reason one should not believe anything. . . In the broad interpretation we can understand that good reason for believing something is true includes reasons that make the belief likely as well as ones that benefit the believer and others” .
Consider for instance W.K. Clifford’s essay “The Ethics of Belief” (1879). In this essay he makes the famous statement that “it is wrong always, everywhere, and for anyone, to believe anything on insufficient evidence” . Of course, I think Martin is right where he criticizes Clifford for including a moral sentiment in his “evidential criterion.” In other words, what evidence is there to support the statement that “it is wrong always, everywhere, and for anyone, to believe anything on insufficient evidence”? Clifford in fact offers somewhat moral reasons (or, “beneficial” reasons) for believing things without sufficient evidence (it has the potential of harming you or others, etc).
Thus, with respect to (4) invoked into our principle, the question is where or not condition (2) holds:
- (2) X is the sort of entity that, if X existed, there would be available evidence that would be adequate to support the view that X exists.
Of course, the X in question is considered to be an all-powerful, all-good and all-knowing God – a being which I myself have argued for on numerous occasions suggesting that there is available evidence that is adequate to support the view that God exists. However, various philosophers and theologians (e.g., Karl Barth, Emil Brunner, etc.) have argued that God is transcendent in such a way that condition (2) could never be met. For instance, protestant theologian Paul Tillich once remarked that “the question of the existence of God can be neither asked nor answered. If asked, it is a question about that which by its very nature is above existence, and therefore the answer. . . implicitly denies the nature of God” .
Of course, this view of God is not one that seems to be very popular today (let alone clear that it is or isn’t popular), however, it would seem to be the case according to Martin that we do not have adequate evidence for believing in God. If we incorporate the idea that the application of (SP’) is only presumptive and could be defeated, Martin thence proposes the Scriven principle extension (SP’E):
- (SP’E) A person is justified in believing that X does not exist if (1) all the available evidence used to support the view that X exists is shown to be inadequate; and (2) X is the sort of entity that, if X exists, then there is a presumption that would be evidence adequate to support the view that X exists; and (3) this presumption has not been defeated although serious efforts have been made to do so; and (4) the area where evidence would appear, if there were any, has been comprehensively examined; and (5) there are no acceptable beneficial reasons to believe that X exists.
Martin suggests that (SP’E) “seems to be justified in terms of our ordinary and scientific practice,”  since, it would seem rather arbitrary to use this principle only in religion where other examples can show its more general demonstrability. Hence, from here Martin offers several a posteriori arguments to suggest that the existence of God is improbable.
God and Omniscience
What does it mean to say that God is omniscient? Of course, we are usually given the general understanding of God’s omniscience as “God knows all things.” But just what exactly does God know? Philosophers have distinguished between three kinds of knowledge:
- (1) Propositional or Factual Knowledge
- (2) Procedural Knowledge (“knowledge-how”)
- (3) Knowledge by Acquaintance
Consider the following sentence: “I know Steven Dunn.” This sentence is claiming to have implicit factual knowledge about the person Steven Dunn as well as knowledge by acquaintance of Steven Dunn. In a similar fashion, to say “I know pain” implies not only detailed factual knowledge of pain but also some direct experience of it. Hence, consider the following definition of omniscience:
- (1) A person P is omniscient = If K is knowledge, then P has K.
where K includes all forms of knowledge – propositional, procedural and knowledge by acquaintance. However, this definition already fails since there are no restrictions on what P can believe; hence, P can even have false beliefs. Furthermore, if person P has some false belief ~B (not-B), since propositional consists of true beliefs, person P would by definition believe that B. Therefore, definition (1) allows for P to have inconsistent beliefs. We need need to better qualify definition to exclude inconsistent beliefs. Suppose the following:
- (2) A person P is omniscient = For every true proposition p, P believes that p and P believe that p IFF P knows that p, and for every sort of knowledge-how H, P has H to the highest degree, and for every aspect A of every entity O, P has direct acquaintance of A.
But we appear to run into another problem. If God is understood so defined in the sense of classical theism – then this definition of omniscience conflicts with God’s disembodiedness or immateriality. For instance, if God were omniscient in this sense, then He would have all knowledge (including knowledge by acquaintance) of “how to do gymnastics exercises on the parallel bars, and He would have this knowledge to the highest degree” . Since God’s omniscience and immateriality conflict (under this definition), therefore God does not exist. Hence, we need to invoke another qualifying definition.
However, suppose we were to operate on the more consistent basis that God doesn’t have knowledge by acquaintance and procedural knowledge, but rather that “it is enough that [God] have in His possession all knowledge that it is logically possible for God to have” . The following definition occurs:
- (3) Person P is omniscient = For any true proposition p, if its is logically possible that P could believe that p, then P that p, and P believes that p IFF P knows that p, and for any sort of knowledge-how H that it is logically possible for P to have, P has H to the highest degree, and for every aspect A of every entity O that it is logically possible for P to be directly acquainted with, P is directly acquainted with A.
Of course, this definition dodges the inconsistency that was drawn out with definition (2). However, this definition faces a problem of its own: “it is logically impossible that God can have knowledge that it is logically possible for humans to have. The result is paradoxical, to say the least” . For instance, one might say that the following is true:
- (a) If person P is omniscient, then P has knowledge that any non-omniscient being has.
Furthermore, that the following is also true:
- (b) If God exists, God has all knowledge that humans have.
Unfortunately, both (a) and (b) are rendered false given definition (3). According to Martin, “The definition conflicts with what is normally meant by ‘omniscient’ and, bracketing omniscience, what one means by ‘God” . Furthermore, definition (3) doesn’t even seem to still capture what is meant when God is said to be omniscient. For instance, consider Martin’s analogy of “McNose”:
Consider a being called McNose. His knowledge is of the highest degree, but McNose only knows how to scratch his nose and only has direct experience of all aspects of his nose’s itching and being scratched. Let us further suppose that all McNose’s beliefs are about his nose’s itching and being scratched and that these beliefs constitute knowledge. Absurdly, McNose is omniscient on definition (3). 
However, maybe we can pose another definition of omniscience that is much more fitting! McNose with respect to omniscient being is perhaps lacking in epistemological perfection – something that we could add into our new understanding of omniscience:
- (4) Person P is omniscient = For any true proposition p, if P’s believing that p would increase P’s epistemological perfection, then P believes p; and P believes that p IFF P knows that p; and for any piece of knowledge-how H that would increase P’s epistemological perfection, then P has H to the highest degree; and for every aspect A of every entity O, if being directly acquainted with A would increase P’s epistemological perfection, then P is directly acquainted with A.
Here it seems that we are no more clear on epistemological perfection in this definition than we are on omniscience in the last definition. For, as we have seen before, God doesn’t have epistemological perfection because humans can have certain knowledge by acquaintance and procedural knowledge that God cannot have. Furthermore, even if one were to allow God to have the knowledge that humans have, it would conflict with some of God’s other characteristics – such as immateriality. Martin thence argues that “God’s omniscience conflicts with His disembodiedness. . . and His omnipotence” .
-  Michael Martin, Atheism: A Philosophical Justification (Temple University Press: 1990) p. 281
-  Antony Flew, “The Presumption of Atheism” in God, Freedom, and Immortality (Promotheus Books: 1984), pp. 13-30
-  Michael Martin (1990), p. 29
-  Ibid., p. 281
-  Michael Striven, Primary Philosophy (McGraw-Hill: 1966) p. 102
-  Michael Martin (1990), p. 282
-  Ibid., p. 30 – emphasis mine.
-  Quoted from Michael Martin, The Case Against Christianity (Temple University Press: 2001) p. 19
-  Quoted from George Smith, Atheism: The Case Against God (Promotheus Books: 1979) p. 33
-  Michael Martin (1990), p. 283
-  Ibid., p. 288
-  Ibid., p. 289
-  Ibid.
-  Ibid.
-  Ibid., pp. 289-290
-  Ibid., p. 292