Posted by: what more January 25, 2006
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Condorcet's Paradox
the basic idea in Arrow's work can be captured in a 3 person, 3 alternatives model.
let the three alternatives (election candidates, say) be x, y and z.
let ">" represent "prefers to"
let ">" be transitive, i.e. x > y and y > z implies x > z
suppose we have the following preferences
Person 1: x > y, y > z
Person 2: y > z, z > x
Person 3: z > x, x > y
What does the society choose using majority (which some claim is democracy)?
Define pair-wise majority as choosing an alternative based on comparisons between only two of the alternatives at a time. What this means is that you have to consider all 3 alternatives, but you do that by considering two at a time. What does the society choose?
Can you come up with a rule so that the society makes a definite choice?