John Humphrys tied himself in knots on the Today programme this morning attempting to rebut David Cameron's claim that AV gives some people two votes. The broadcaster said: "I have a second preference as well as you or anybody else and you count them again as well, so you don't count some people's votes more than others."
This allowed a gleeful Cameron to respond: "You are wrong. If you vote for the Labour candidate and I vote for the Monster Raving Loony candidate and the Monster Raving Loony comes last, my second preference is then counted again . . . It is quite worrying if actually the lead broadcaster on the BBC doesn't understand the system. You don't understand the system you are supposed to be explaining to the public. I do think that's worrying. Back to school."
What Humphrys was rather clumsily attempting to explain is that first preferences are also counted twice. The difference is that your vote goes to the same candidate in each round. For instance, in the 2002 French presidential election, if you voted for Lionel Jospin in the first round and Jacques Chirac in the second round (to keep Jean-Marie Le Pen out), you did not get more votes than someone who voted for Chirac in both rounds. A transferred vote is not the same as a multiple vote.
It's not a complicated argument, but it's one that the Yes campaign, to its cost, has struggled to make since the campaign began.