Duncan Black


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Scottish economist; one of the modern pioneers of analytically rigorous political science. From his time as a student of physics and economics in Glasgow (1929–33), he dreamt of formulating a ‘Pure Science of Politics’ in which any political system could be represented by a set of definitions and axioms. His most important contribution, the median voter theorem, came to him in 1942. It states that if all members of a voting body (committee, legislature, or electorate) recognize one main dimension in politics (left–right, for example, so that all leftists like the rightmost option least, all rightists like the leftmost option least, and everybody else dislikes an option more the further it is from their favourite position), then the median voter's favourite position will win in any reasonable voting procedure. Hence the median voter may stand for the whole voting body. The median voter theorem does not necessarily hold in more than one dimension, as Black was the first to see, because then there is always the possibility of majority‐rule cycling. But where one dimension dominates the others, as in Congressional committees or (probably) UK voting behaviour in general elections, it is a powerful predictor of convergence on the median voter's position. In the long run, politicians who diverge far from this are unlikely to be successful, even if protected by an electoral system for some time.

Subjects: Politics — Economics.

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