Razor Swift

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Absence Of Evidence Is Not Evidence

Evidence Collection

Photo Attribution: Main121 (public domain)

Rule It Out First

There’s an interesting sentiment that I hear on occasion when conversing with atheists about God. I’ve been informed that absence of evidence is evidence of absence. I admit that it seems to be convincing, but only to those that have no training in formal logic. After all, if there’s no evidence for God (in the form of tangibility -usually the type requested by atheists) then this absence seems to be a blow to his existence. Right? Not exactly. We’re going to examine the modus tollens argument (Latin; the way that denies by denying) to see if this type of reasoning is valid or not. The argument goes like this:

  • If X is true then Y is true.
  • Y is false.
  • Therefore X is false.

A modus tollens argument is not based on absence of evidence, but rather the presence of contrary evidence that contradicts what we would expect to see if a proposition were true. Example, the reason people can know that I’m not a leprechaun is not because of the absence of evidence that I am a leprechaun, it’s the presence of evidence that I’m not a leprechaun. There’s good evidence that shows I’m a normal full grown human. The atheist philosopher Austin Dacey says: “What if these arguments purporting to establish that God exists are failures? . . . Must we then conclude that God does not exist? No. Lack of supporting reasons or evidence for a proposition does not show that the proposition is false. [1] He is clearly keeping the modus tollens in mind with such a statement.

Here’s another example which shows that absence of evidence is not evidence of absence. Let’s say that I come home from work and find out that my drumset is missing. The absence of evidence that it was stolen (e. g. no broken windows; no signs of forced entry etc) doesn’t automatically mean it was not stolen. It could have been, but it also could have been borrowed by my brother in law or wife etc. The same can be said for a crime scene investigation where there’s a person laying dead in his bed. The absence of evidence that it was murder (verses suicide or natural causes), doesn’t rule out that it wasn’t murder. In reality, it very well could be murder but the evidence may never surface.

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Endnotes

1. The Case for Humanism, 2003, pg. 162

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