The Burden of Proof and the Presumption of Atheism

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Sir Anthony FlewWhich of the following alternatives is most reasonable:

  1. In the absence of evidence for God’s existence, it is still more reasonable to hold that God exists (theism).
  2. In the absence of evidence for God’s existence, it is more reasonable to conclude that God does not exist (atheism).
  3. In the absence of evidence for God’s existence, it is more reasonable to conclude that we do not know if God exists (agnosticism).

To determine this we explore the nature of the ad ignorantiam fallacy and how it applies to the question of God’s existence.

The Ad Ignorantiam Fallacy
It is of course a truism that just because a proposition has not been proven to be true does not mean the proposition is false and vice versa. The ad ignorantiam fallacy, in a nutshell, is to unreasonably force an opponent to bear the burden of proof when there is an absence of evidence. This fallacy can take two forms:

Form A: Proposition P has not been proven to be true, therefore P is false
Form B: Proposition P has not been proven to be false, therefore P is true

An example of a fallacy with each form would be:

  1. “Since one cannot prove that their experience of the external world is true, therefore their experience of the external world is false.”
  2. “Since one cannot prove that Mr. Jones has not committed acts of espionage, therefore it is true that he is a spy.”

Both 1 and 2 are fallacious. But even though both are an instances of the ad ignorantiam fallacy, it is not always the case that other propositions with the same form are such. Other arguments having these same forms are not always unreasonable. Consider:

  1. “Since there is no proof that Mr. Jones has committed acts of espionage, therefore, he is not a spy.”
  2. “Since my experience of the external world has never been proven false, therefore it is true.”

Both of the these latter statements are reasonable inferences yet they have the same form as those that commit the ad ignorantiam fallacy. This tells us that appealing to ignorance and lack of evidence is not always fallacious. Context and subject matter make all the difference.

So when is it reasonable to appeal to ignorance and when is it not? It is not always easy to determine who should shoulder the burden of proof, but it seems to me there are at least four criteria:

  1. All other factors being equal, the greater burden of proof rests with someone whose claim has the least initial plausibility. If someone wants to claim we do not experience the external world but instead are just brains in a vat under the control of an evil scientist, this is very implausible and such a person making the claim shoulders the burden of proof. It is fallacious to force a person to disprove a counterintuitive claim.
  2. All other factors being equal, the greater burden of proof lies with the person making an affirmative claim, rather than with the person who is denying that claim.
  3. Sometimes special situations may call for a shift in burden of proof. If say a human life is at stake, the burden of proof should fall on the claim that may cause harm.
  4. All other factors being equal, reasonable expectations can determine when an absence of apparent evidence constitutes a proposition as false. Here we ask how much evidence should we expect in relation to what we have. For example, if someone claims there is a gorilla in the room – the fact that we cannot see the gorilla, hear the gorilla, etc., is an absence of evidence that disproves this proposition. However, if someone says there is a mosquito in the room, then an absence of evidence  (not seeing or hearing it) does not disprove the proposition because our reasonable expectations of evidence have changed. In more borderline cases, we should avoid dogmatic conclusions on both sides, for example:

“No one has ever proved that Bigfoot exists, so it must not exist.”
“No one has ever proved that the Bigfoot does not exist, so it must exist.”

Both sides here commit the fallacy of appealing to ignorance in that they derive unwarranted certitude when a more reserved stance seems called for. The certitude on both sides is unwarranted for there seems to be no clear way of establishing how much evidence to expect relative to what we have, nor can this determination even be made until all of the appropriate areas where such evidence would be found have been adequately surveyed. A lesser degree of certitude, or even agnosticism, is warranted here.

Given these criteria for the ad ignorantiam, we now apply them to the case of God’s existence.

The Burden of Proof and the Existence of God
It seems to me that criteria 1 and 3 are not applicable to the existence of God debate. The existence of God is not prima facie implausible, and 3 really does not apply here at all. I would also add that 2 is perhaps the least important of all the criteria. That is, implausibility, harm and reasonable expectations of evidence will always override whether or not a proposition is affirmative or not, so Flew’s exclusive emphasis on 2 is far too simplistic. 2 alone is insufficient in establishing the burden of proof. If that were the case, then anyone making an affirmative claim about obvious truths like “This is my arm” or “My experience of the external world is veridical” would be unreasonably forced to attempt to prove the obvious. So the affirmative proposition criterion alone is insufficient.

So if I’m right about this then that leaves us with criterion 4. An absence of evidence indicating evidence of absence is only telling when the evidence we have is far less than what we would expect. In the case of God, the presumption of atheism presupposes a) we have adequately surveyed the area in which we would find such evidence and b) that the evidence we have for God is far less than what we would expect. But how can 1 and 2 be known as true? Now both of these are affirmative propositions, and so by Flew’s own criterion he should marshal support for them. Far from relieving himself with the burden of proof, now the atheist is burdened with showing both that a) we have adequately surveyed the area in which evidence would be found and b) what we come up with is far less than what we would expect if God existed, for if God exists he would have left more traces of his existence.

Suppose there are no successful proofs for God’s existence – what is the reasonable conclusion we should draw from this absence of evidence? Antony Flew wants to take the presumption of atheism as the reasonable default position, other theists like Plantinga take theism as “properly basic”, however it seems to me a third option is best, that in absence of an absolute proof of God’s existence, agnosticism is the most reasonable position. We should avoid dogmatic assertions on either side, and so in such a hypothetical scenario both of these statements are fallacious:

“No one has ever proved that God exists, so he must not exist.”
“No one has ever proved that God does not exist, so he must exist.”

And I would say the same goes for the theist, given an absolute absence of evidence it is fallacious to conclude that God exists. But what if the absence of evidence is not absolute? Any reasonable atheist should admit that the existence of God is not wholly unsupported – there are at least some arguments for it. Even if these arguments are not accepted as conclusive, they merit some degree of probability. Now it’s not clear how much evidence to expect from God given his existence, nor can one establish that all of the relevant areas where evidence may be found have been adequately covered.  Yet it seems to me that the evidence for God’s existence is greater than the evidence for the existence of Bigfoot, and if we are rash in concluding with certitude that Bigfoot does not exist because of a lack of evidence, a fortiori this is the case with God.

So even if the theist fails to establish his case, at best that simply leaves the reasonable man with agnosticism, and to infer atheism from this would be to commit the ad ignorantiam fallacy. And this is significant, for that means, reasonably speaking, agnosticism is the theoretical starting point. The more plausible the arguments for God’s existence are, the more the reasonable man moves from agnosticism to theism.