Rationality & Irrationality
or
Why are we* so foolish,
and what can we do about it?
* Present company excepted, of course.
Rationality and Irrationality
Rationality & Irrationality
• Why are we so foolish?
– The rise and fall of rationality on cognitive science
– An introduction to ‘inevitable illusions’
• What can we do it about our foolishness?
Rationality and Irrationality
The rise and fall of human rationality
• (Some proponents of) Cognitive science had high hopes of
being ‘a science of ideal rationality’ when it emerged
– The cleave between competence (~computation) and
performance (~biology)
– This goal was stymied by evidence of:
• Lack of general problem-solving methods
– Compartmentalization of knowledge
• Context effects
• A growth industry in the study of human
foolishness: Cognitive illusions
Rationality and Irrationality
The rise and fall of rationality on cognitive science
• Why should this be so?
“If no organic being excepting man had possessed any
mental power, or if his powers had been of a wholly
different nature from those of the lower animals, then we
should never have been able to convince ourselves that
our high faculties had been gradually developed. But it
can be shewn that there is no fundamental difference of
this kind. We must also admit that there is a much wider
interval in mental power between one of the lowest fishes,
as a lamprey or lancelet, and one of the higher apes, than
between an ape and man; yet this interval is filled up by
numberless gradations.”
Charles Darwin/ The Descent Of Man
Rationality and Irrationality
• The brain is constructed to find reward in apparent
solutions (coherence); which are not the same as
solutions (cf. Damasio, Cytowic, Bernard [not to
mention Wittgenstein & Peirce])
‘Executive’
functions
Limbic circuit
Rationality and Irrationality
Cognitive Illusion 1: Over-confidence
• We are not good at judging our own confidence levels
• We tend to systematically err on the high side, and to resist
attempts at correction
• The error increases as we become more certain
• We institutionalize this error by demanding certainty from
our experts and instilling certainty in them
– Question: Are there any good reasons to make this demand?
Rationality and Irrationality
Cognitive Illusion 2: Magical thinking
• We put great confidence in signs that derive from folk
beliefs: illusory correlations
– We will see some worrisome evidence of this in a later reading in
this class
• Moreover, we look for evidence to support and sustain an
priori beliefs in correlations
• we are easily taught to do so, even in the absence of
evidence or the presence of counter-evidence
– Cancer cell recognition: Watzlawick
Rationality and Irrationality
Cognitive Illusion 3: 20/20 Hindsight
• The fact that something actually has happened is taken to
mean that:
– it had a high probability of happening
– that we would have known this beforehand
Rationality and Irrationality
Cognitive Illusion 4: Anchoring
• We use initial reference points to anchor future estimates
– We do so even when those initial reference points are
(known to be) random
Rationality and Irrationality
Cognitive Illusion 5: Taking the easy way out (Availability)
• We will use an easier representation rather than a more
complex one
– The easier it is to bring an event to mind, the more
likely we are to judge it as frequent (Uncle George’s
Pancakes fallacy)
– This leads to under-estimation of what is frequent
(suicide) and over-estimation of what is not (murder),
and thereby mis-estimations of coincidence
– Homework: Pick a random number (under 100 is best)
and be ready for coincidences in everyday life about it.
Report back to us.
Rationality and Irrationality
Cognitive Illusion 6: Probability blindness
• We don’t equate equal probabilities (though fate does),
especially at the extremes of the probability range
– We prefer an increase from 0.94 to 0.99 from one to
0.38 to 0.42, or something which reduces risk from
0.001 to 0 to something which reduces it from 0.002 to
0.001
• We reduce probabilities to certainties and deny that
population probabilities apply to individual cases
• We mis-estimate co-variation
Rationality and Irrationality
Covariation mis-estimation
Lives
Has symptom X
Doesn’t have
symptom X
Dies
12
6
6
3
From: Arkes, Harkness, & Biber (1980)
Question: How strong is the relation between symptom X and death?
(How worried should you be, on a scale of 1-100, if you have symptom X?)
Rationality and Irrationality
Cognitive Illusion 7: Story-telling
• We over-estimate the probability of coherent fictions with
many parts (conjunction illusion)
– Note that chains of events MUST be less probable than
their weakest link (assuming we have no absolute
certainty, which we never do).
• Both research and real life tell us that people find
arguments more compelling when they support what they
already believe anyway.
Rationality and Irrationality
What can we do about our foolishness?
1.) Distrust certainty; Cultivate scepticism
“Doubt is an uncomfortable condition, but certainty is a
ridiculous one.”
- Voltaire
2.) Keep score; Don’t rely on your memory.
- Keep clinical records, compile databases; consult them
before you act.
3.) Do the math.
- Use Bayes’ Theorem; run statistical tests; look at
distribution shapes etc.
Rationality and Irrationality
What can we do about our foolishness? II
4.) Consider plausible alternatives
- Research shows that this reduces hind-sight bias in some
cases
5.) Watch out for the ‘buddy-buddy’ syndrome
“The cognitive degradation and feckless vocalization
characteristic of committees are too well-known to require
comment.”
- Paul Meehl
Rationality and Irrationality
What can we do about our foolishness? III
6.) Don’t weight all evidence equally; ignore irrelevancies
- Evidence must be differentially relevant (distinguish
between actual possibilities) to be considered
- Barnum statements: true of practically everyone.
7.) Distinguish between inclusion and exclusion criteria
- Failure to have an accessory symptom of X is not
evidence against a diagnosis of X
8.) Remember reliability bounds
- An insignificant difference on a test result is…
insignificant
Rationality and Irrationality
What can we do about our foolishness? IV
9.) Don’t mistake soft-headedness for soft-heartedness
10.) Be courageous: Speak up for rationality!
- Don’t be cowed by people who haven’t read or
understood Bayes’ Theorem etc.
- Insist on doing your job the right way, and don’t back
down.
Rationality and Irrationality
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Questions etc.
Coincidence example from Piatelli-Palmarini: How many
people need we have in a room to have a 50% chance that
two have the same birthday?
Is rationality always best?
What is the role of authoritarianism in affecting perceptual
and moral judgments?
What is the effect of these inevitable illusions in today’s
world of mass media? (Why might the WWW both hinder
and help rational analysis of probabilities?)
How can we harness these illusions to foster individual
well being and social harmony (without also fostering
harmful delusion)?
Rationality and Irrationality