“Absence of evidence is not evidence of absence.”
…except that, yes, it is. It’s evident that when one expects evidence if a thing were true, a lack of evidence suggests the thing is not true. A fun example: If there were a dragon living in your garage, you might expect some evidence for that, and the lack of any such evidence compels you to disbelieve the proposition “a dragon lives in my garage.” It’s the same reason hikers in the Midwest take no precautions against polar bears. If polar bears lived in the Midwest, we would expect evidence to have surfaced by now. It hasn’t, and this lack of evidence inspires a positive conclusion.
Both examples above consist of our drawing simple conclusions on the basis of a lack of evidence for questions most wouldn’t think to ask. After all, we don’t generally decide whether or not to believe something (e.g. “a dragon lives in my garage”) until we have some reason to suppose it might be true. The problem occurs once we do have cause to consider whether something is true, at which point our idiom about the “absence of evidence” represents a non-trivial defect in the way we sometimes evaluate evidence.
We tend not to notice when our beliefs about the world would be better attested if true. We are overly content with any evidence at all which seems to support our position, and we forget altogether that said evidence must be weighed against the amount of evidence we would expect. If a child blamed a scorched wall in the garage on a dragon, we might ask why we never see or hear it. “Where are the dragon’s droppings?!” we would demand, shaking our son by the shoulders. We do this not because the evidence in question (the burnt wall) is inconsistent with the “live-in dragon” explanation (it isn’t!) but because we would expect rather more evidence in that event.
In the interest of those restlessly wondering how this principle will serve my anti-Christian agenda, I will hurry to a more practical application.
Jesus is alleged to have made quite a splash in his day as a major religious figure. He’s supposed to have garnered the attention of notable world leaders, and his ascension into heaven is traditionally said to have been witnessed by five hundred people. Christians believe these facts to be true, and non-Christians by and large do not. It might appear as though we have reached an impasse. What a relief that we haven’t.
It’s true that any absence of evidence on this issue cannot be proof of absence – we can never know with certainty that Jesus did not ascend into heaven. What we can do is examine what evidence we have available to us in light of (this is the part we so often neglect) what evidence we would expect to have if the claims were true.
The supporting evidence we have is Christian literature, particularly the gospels, written decades and centuries after the events were alleged to have taken place, by non-eyewitnesses, in a different language and different country, based on an oral tradition in circulation for the express purpose of gaining converts. Like the scorched wall in the garage, the existence of the gospels is certainly consistent with the proposed explanation, but what other evidence might we expect to complement them in a world where Christian claims about Jesus were true?
If even half of the ostentatious claims about Jesus were veridical, I think it is more than fair to expect some mention of Jesus by a Greek, Roman, or other non-Christian source from Jesus’ day. Recall that Jesus was raised from the dead, after which all the graves in Jerusalem opened, and the dead roamed free in the city. As mentioned, hundreds are supposed to have witnessed his glorious ascent to heaven. He raised the dead, healed droves of sick, and fed thousands with a few loaves and fish. The gospels record that he created a massive stir in the Jewish and Roman worlds in his time. So how many hundreds of pagan and Roman records date within the decades following Jesus’ death? Zero hundreds. None at all.
Depending on which side you take, there is either one first century, non-Christian historical source for Jesus or there were none. The only references we have are two fleeting (and highly suspect) passages from the Jewish historian Josephus which were likely tampered with by later Christian scribes. I think it’s pretty clear that two short references from a single historian writing decades after the alleged events are less than we would expect given the nature of the gospels’ claims. Yet there are no first century records of Jesus, no eye-witness accounts, nor as much as a casual reference to him in a letter. Not until a full century after Jesus lived did the Roman historian Tacitus finally break the silence with a brief allusion to Jesus having been crucified under Pilate (which he probably was).
It stretches credulity that Jesus made the impact he is written to have made in his lifetime, and that no non-Christian source thought to mention it until decades and centuries after the fact. The evidence we have suggests that Jesus was indeed a very important figure while he lived, but only to a small group of followers who later came to believe he had been raised from the dead. If you simply look at the evidence we have, things don’t look too shabby at first. We have the gospels. A Jewish historian may have mentioned Jesus. Paul claims to have had a vision of Jesus. The trouble doesn’t start until you weigh the evidence against reasonable expectations, at which point it’s hard to see how such scanty evidence is sufficient to satisfy anyone. It’s a scorch on the wall! There are a trillion explanations, each of them more likely than the one being proposed, not merely because dragons are unlikely creatures but because there would be more evidence for the claim if it were true.
This is a simple object lesson to illustrate the broader point: ask not only, “What evidence do I have for X?” but also “What evidence should I expect to have for X?” If we fail to do this, we risk quite a mess. Our world is, frankly, in danger of becoming the sort of place in which billions of people hold fast to varying and contradictory convictions on every topic; in which we disproportionately measure the evidence in favor of our pre-existing beliefs; and in which we allow all manner of implausible explanations to account for youthful mischief in the garage.