You know how conversations go, off down one tangent and then down another. Before you know it you turn back and wonder: how did we ever arrive here?
And so it was that the last thread began with me presenting an argument for testimony as a properly basic way to learn about the world, and it ended up (at least so far) with gaga challenging me to provide the grounds on which I would reject ancient testimony attesting to the existence of giant spiders that ate camels.
That's right. Giant spider-eating camels. I mean camel spiders are freaky enough (as Iraq veterans will tell you), but camel eating spiders? Yikes.
I offered three points by way of reply, but it is this one which apparently set of gaga's "irony meter":
"I am strongly inclined to reject it [that is, the testimony that such giant spiders exist] not least because one should expect some evidence from natural history that such a creature existed, and of course none exists. This absence of evidence constitutes a defeater."
Quickly comes gaga's delighted reply:
"You owe me a new irony meter. Absence of evidence is evidence of absence... coming from a *theologian* that's rich."
Now why am I bothering with this? Well because there actually is an important point here.
Let's begin here: why does gaga find this "rich" coming from a theologian? (And why does he add a * on each side of theologian?) Presumably because atheists often argue that absence of evidence for God's existence is evidence of absence. And if this is sustainable as a piece of reasoning here then they can take a small step from the absence of evidence for God (which would be mere agnosticism or, as is sometimes said "weak atheism") to actual disbelief in God (atheism proper, or "strong atheism" or perhaps "machismo atheism").
Thus, if I adopt the absence of evidence is evidence of absence principle, then the atheist can use it as well. And so I am basically shooting myself in the foot, buffoon that I am.
But all is not lost. In fact, gaga's irony meter is set improperly like a smoke alarm that screeches at the hint of burnt toast.
Actually in some cases absence of evidence is evidence of absence, but not in other cases. It all depends. The cases where absence of evidence is absence of evidence is precisely those cases where we should expect to see evidence and yet can find none.
For example: you inspect your tent for mice. Based on the fact that you find none, you conclude that there are none. Absence of evidence here is indeed evidence of absence.
But now you inspect your tent looking for a bug too small to be seen with the naked eye (perhaps the bugs Alvin Plantinga calls "noseeums"). The fact that you don't see these bugs is not evidence that they are not in the tent since they're too small to be seen. In this case absence of evidence is not evidence of absence and thus you should be agnostic.
When it came to giant spiders that eat camels, these are obviously like mice in the tent -- the kind of entity for which there should be evidence of its existence -- rather than like noseeums --the kind of entity for which there should not.
So in the case of giant camel eating spiders I agree that absence of evidence is evidence of absence.
But what about God? Should we expect evidence of God's existence such that if we do not find it then we can rightly conclude that God does not exist?
Here I would first want to contend with the notion that there is no evidence. I think that there is adequate evidence for God's existence from a range of sources. (Peruse William Lane Craig or Gary Habermas' many university debates for some standard examples.)
Admittedly, such evidence is not overwhelming or ineluctable (like most everything else in formal debate), and it faces a potential defeater in the existence of evil. But there are possible explanations for this "problem of divine hiddenness". For instance, if God's ultimate purpose is not simply that we know he exists but that we come into relationship with him, then it may be that the current degree of evidence is precisely sufficient to accomplish that purpose. It is tough to know that this isn't the case.
These quick considerations leave me somewhat ambivalent about the absence of evidence principle when it comes to God, while still happy to invoke it when it comes to giant camel eating spiders.