While there are no timeless arguments in the history of political thought, there may indeed be perennial questions. If anything is recurrent throughout Western thought, it is likely to be the abhorrence of conflict and the quest for stability and peace. Political societies require a degree of internal peace to function. Since they imply division, political parties thus pose a problem for political theory. Extreme partisan divisions threaten to undermine trust among citizens, tear societies apart and constitutions asunder, and degenerate into violent strife and even civil war. Yet parties can also help to pacify and domesticate conflict. Party is an instrument for organising competition and adjudicating between interests and opinions. Any politics worthy of the name entails competition between ‘ins’ and ‘outs’, involving a mixture of interest and principle. Politics is not just about competition, but this is a crucial aspect of any politics that would be recognisable to us in the twenty-first-century Western world, as in many other parts of the world. In modern large-scale societies, effective political action requires numbers and organisation. Moreover, parties and partisanship are natural concomitants of modern understandings of liberty: in 2liberal regimes we have the right to form opinions and associate with others of similar views. Securing political stability has been a concern for political thinkers since at least Thucydides, but the role played by parties in channelling or augmenting division is a more recent concern – one on which this book is focused.