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gjm comments on Open thread, August 4 - 10, 2014 - Less Wrong Discussion

5 Post author: polymathwannabe 04 August 2014 12:20PM

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Comment author: fubarobfusco 04 August 2014 09:32:34PM 6 points [-]

On the limits of rationality given flawed minds —

There is some fraction of the human species that suffers from florid delusions, due to schizophrenia, paraphrenia, mania, or other mental illnesses. Let's call this fraction D. By a self-sampling assumption, any person has a D chance of being a person who is suffering from delusions. D is markedly greater than one in seven billion, since delusional disorders are reported; there is at least one living human suffering from delusions.

Given any sufficiently interesting set of priors, there are some possible beliefs that have a less than D chance of being true. For instance, Ptolemaic geocentrism seems to me to have a less than D chance of being true. So does the assertion "space aliens are intervening in my life to cause me suffering as an experiment."

If I believe that a belief B has a < D chance of being true, and then I receive what I think is strong evidence supporting B, how can I distinguish the cases "B is true, despite my previous belief that it is quite unlikely" and "I have developed a delusional disorder, despite delusional disorders being quite rare"?

Comment author: gjm 05 August 2014 10:15:49AM 2 points [-]

The relevant number is probably not D (the fraction of people who suffer from delusions) but a smaller number D0 (the fraction of people who suffer from this particular kind of delusion). In fact, not D0 but the probably-larger-in-this-context number D1 (the fraction of people in situations like yours before this happened who suffer from the particular delusion in question).

On the other hand, something like the original D is also relevant: the fraction of people-like-you whose reasoning processes are disturbed in a way that would make you unable to evaluate the available evidence (including, e.g., your knowledge of D1) correctly.

Aside from those quibbles, some other things you can do (mostly already mentioned by others here):

  • Talk to other people whom you consider sane and sensible and intelligent.
  • Check your reasoning carefully. Pay particular attention to points about which you feel strong emotions.
  • Look for other signs of delusions.
  • Apply something resembling scientific method: look for explicitly checkable things that should be true if B and false if not-B, and check them.
  • Be aware that in the end one really can't reliably distinguish delusions from not-delusions from the inside.
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