You can't prove it's impossible!

[reddragdiva]

A common sophistry which really annoys me is the one that conflates an utterly negligible probability with a non-negligible one. The argument goes:

1. There is technically no such thing as certainty.
2. Therefore, [argument I don't like] is not absolutely certain.
3. Therefore, the uncertainty in [argument I don't like] is non-negligible.

Step 3 is the tricky one. Humans are, in general, really bad at feeling the difference between epsilon uncertainty and sufficient uncertainty to be worth taking notice of — they can't tell a nonzero chance from one that's worth paying attention to ever. (This is why people buy lottery tickets.)

It’s a terrible, terrible argument, and an unfortunately common one. It needs to be bludgeoned to death every time it’s brought up.

Comments

[tcpip]

Ahh, my bad. That's a third issue!

[reddragdiva]

This is a general human stupidity rant, not a philosophers' stupidity rant ;-)

[reddragdiva]

I need to find out what this fallacy is actually called. It's common enough that it's got to have a name.

[tcpip]

You can call it the fallacy of magnification, to adopt the word from cognitive psychology, or more specifically, a "fallacy of magnification arising from cognitive bias".

Essentially the person is turning negligible "corner cases" in a proposition into a central flaw, because they want the argument to be centrally flawed. They are also ignoring that any rational proposition must, by its very nature, have fallible components.

[reddragdiva]

I could go for a neologism if necessary (basically I'll make the above a RationalWiki article), but I'd rather have its proper name if it has one.

The essence of crankdom is turning a negligible probability into a non-negligible one. Look into any crank idea (9/11, birthers, cold fusion) and you'll find a step where a negligible probability is treated as non-negligible.

[tcpip]

The essence of crankdom is turning a negligible probability into a non-negligible one.

Nicely put.