The voter (or pair of voters) in the exact middle of a ranking of voters along some issue dimension, e.g. from the most left‐wing to the most right‐wing. In the 1940s Duncan Black proved the median voter theorem, which states that the median voter's preferred candidate (or policy) is bound to win against any one other, by any well‐behaved voting system. This result was popularized in Anthony Downs's An Economic Theory of Democracy (1957). Downs further predicted that rational politicians would converge on the issue position of the median voter because, if they went anywhere else, the opposition could win by sidling up on the majority side of them. This centripetal force is often called Downsian competition. When there is more than one issue dimension, the median voter theorem only applies in very unlikely conditions of balance. Instead, cycles may exist, although they are often not revealed. See Riker; heresthetic(s).