Why do American parties hold conventions?

They're expensive, tricky to organise, and - as the Republicans are finding this week - can be strewn with difficulties. Why do the two main US parties hold conventions to select a candidate? First published on Thu, 21 Jul 2016 as Why do American parties hold conventions?. To find out more visit The Open University's Openlearn website. Creative Commons BY-ND 4.0 2016