5X5 Episode 50

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5X5 Episode 50
Argument from Ignorance
15th December 2008

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5X5 49 5X5 51
Skeptical Rogues
S: Steven Novella
R: Rebecca Watson
B: Bob Novella
J: Jay Novella
E: Evan Bernstein
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Skepticism 101 - The Argument from Ignorance[edit]

You're listening to the Skeptics' Guide 5x5, five minutes with five skeptics, with Steve, Jay, Rebecca, Bob and Evan.

S: This is the SGU 5X5 and our series on Skepticism 101 and the topic for tonight is the logical fallacy known as the argument from ignorance.

J: (in silly voice) All I know is I saw a ghost.


R: (in silly voice) Why you gotta be so ignunt Jay?

J: (in silly voice) It's all I know, I know what I saw, and I saw a ghost.

R: Well I don't know what else it could be, therefore it must be a ghost.

E: There you go.

J: (in silly voice) Of course it is, it had to be.

S: So an argument from ignorance is whenever a positive claim is made based on the absence of information, or the absence of knowledge. Within skeptical circles I think this most often applies to the UFO sighting. "I saw a light in the sky, I have no idea what it was, therefore it was an alien space craft."

R: It's also known as the God of the gaps fallacy, where you just sort of fill in whatever gaps in our knowledge we have, you just fill in with whatever deity or supernatural explanation you want because we can't come up with a better explanation, so you might as well, but that's not a good thing 'cos to me that ends the conversation. Instead of saying "we don't know about this, therefore we should explore it further," you're just sort of putting a period at the end of the sentence and saying "well, it must be something supernatural, therefore - done."

E: That's right Rebecca, and this is a favorite logical fallacy employed by those proponents of [[[wikipedia:Intelligent design|Intelligent design]]. Steve, you blogged about this not too long ago, saying "what IDers argue is that because we cannot provide an adequate evolutionary explanation for the complexity we see in life, it must have been deliberately designed."[1] And that's a classic argument from ignorance.

J: Here's a great example from history. Senator Joe McCarthy said this: "I do not have much information on Case 40 except the general statement of the agency… that there is nothing in the files to disprove his Communist connections."[2] There's the—

S: Right.

J: —There's the fallacy right there for you.

S: But of course science really can only advance by making a positive case for something. So, how do we know that that light in the sky was an alien space craft? Well, what are the markers of an alien space craft? What features about it positively link it to an alien space craft, not just the absence of information about it being something else. And also, as Rebecca said, when that becomes the God of the gaps argument whenever you use this argument, an argument from ignorance, in order to prematurely settle on a conclusion without considering other possibilities. There are an infinite number of things an unknown light in the sky can be. There's no reason to say that it's any one of those things just based upon the absence of any positive identification.

B: And also it's important to realize, like most other fallacies, that there are exceptions, and it's important to know what those exceptions are. Sometimes an inference can be made when there is a lack of evidence. For example, if there is no train arrival listed at a train station in the next hour, now we're assuming here of course that the schedule, that all scheduled arrivals are listed, that's the hidden premise here, therefore you can conclude that there isn't a scheduled train arrival at the station in the next hour.

S: I wouldn't say that's an exception, that's just not an argument from ignorance.

B: Yeah, but you're using your ignorance of something to make an inference about something else, so you're drawing a conclusion based on a lack of knowledge, I mean, isn't that the definition of this fallacy?

S: I disagree, it's not a lack of knowledge, it's knowledge for the lack of a listing with a reasonable premise that all arrivals are listed. So I think that that can easily be confused with the argument from ignorance. So now you're talking more about absence of evidence and the evidence of absence. The absence of evidence does not prove that something is absent but it is certainly evidence for it. But that's a common misunderstanding. When the existence of a phenomenon means that there is certain evidence that should be present, the absence of that evidence does in fact argue against the existence of that phenomenon. But I think that's a different logical point than the argument from ignorance which is going from the absence of knowledge to a specific positive claim. It's the specificity that is the problem as opposed to just saying "we don't know what it is, it could be all these various things, it could be an alien space craft, we don't know that it isn't," but not knowing that it isn't is not the same thing as knowing that it is.

J: I've got a quote here, I think it's from Sigmund Freud: "The weakness of my argument does not imply the strength of yours." Whoever it's from, I like it.

S: SGU 5x5 is a companion podcast to the Skeptics' Guide to the Universe, a weekly science podcast brought to you by the New England Skeptical Society in association with skepchick.org. For more information on this and other episodes, visit our website at www.theskepticsguide.org. Music is provided by Jake Wilson.



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  1. Intelligent Design and the Argument From Ignorance, NeurologicaBlog, 13th July 2007
  2. Richard H. Rovere, Senator Joe McCarthy (Methuen, 1960), pp. 106-107 (FallacyFiles.org link)