A theorem (proved by Allan Gibbard and Mark Satterthwaite) tells us that, if there are three or more candidates, any voting system which is not a dictatorship and which allows the possibility of any candidate winning, is susceptible to tactical voting.So the common assertion – on both the Electoral Reform Society and the Yes! to Fairer Votes web pages – that AV "eliminates the need for tactical voting", is false.There is a celebrated theorem proved by Kenneth Arrow which can be stated with a shocking simplicity: "No fair voting system exists if there are three or more parties". At its heart is a subtlety which arises when combining the orders of preference of individual voters. These orderings have the simple-sounding property that if a voter prefers A to B and also prefers B to C, then the voter prefers A to C.FPTP, AV, PR or Tom & Jerry: the result is that nobody will be happy if their candidate does not win.
Ben Owen ● 5459d