The Puzzle of Backbench Assent

This chapter introduces the two aims of the book. First, how to measure the role played by policy preferences for achieving party unity in floor votes, that is, to what extent parliamentary parties are united because legislators in them agree with each other and disagree those from other parties. Second, how to explain the gap between the parliamentary floor voting unity expected based on preferences alone, and what is observed. In other words, why do MPs do not always vote their pure preferences? The chapter introduces the key question: Does this happen because of a desire for re-election and promotion, or because of the long-term benefits of belonging to the united party? The chapter then discusses the benefits, costs, and sources of party unity, and the insights that can be gained from studying attitudes to party unity.