Introduction

Do parties force or entice their members to vote together in spite of their disagreements about policy, or do party members vote together because they already agree over policy? The high levels of cohesion displayed by parliamentary parties tend to discourage students of parliamentary politics from asking this question. There is, perhaps, an underlying assumption that if parliamentary parties are highly cohesive, it must be because they can and do enforce discipline. For Krehbiel (1993, 1999), however, the answer to this question is not clear a priori, and the inferential link between policy preferences and discipline, on the one hand, and individual loyalty and party unity, on the other, not necessarily correct; MPs' voting behaviour could just as well be determined by their ‘preferenceship’, that is, by their ideological proximity to various voting coalitions in the chamber, as by their party affiliation.

There is a temptation to dismiss preferenceship out of hand as an abstraction that is too far removed from the realities of parliamentary politics to yield valuable insights; this temptation should be resisted. Preferenceship, after all, is less a comprehensive model of legislative politics than a starting-point for further investigation.