Affective polarization, a concept that originated in the USA, has increasingly been studied in Europe’s multi-party systems. This form of polarization refers to the extent to which party supporters dislike one another – or, more technically, to the difference between the positive feelings towards the supporters of one’s own political party and the negative feelings towards the supporters of other parties. Measuring this gap in Europe’s multi-party systems requires researchers to make various important decisions relating to conceptualization and measurement. Often, our focus could instead lie on assessing partisan hostility or negative party affect, which is easier to measure. While recent research on affective polarization in Europe has already taught USA lot, both about affective polarization and about political conflict in Europe, I nevertheless suggest that research in this field faces four challenges, namely developing better measures, more sophisticated theories, clearer accounts of affective polarization’s importance and successful ways of reducing negative party affect, if this is indeed desirable.

This study investigates to what extent affective polarization, and more specifically hostility towards opposing party supporters, finds its roots in ideological differences. We look into the way out-groups are constructed when there are more than two political parties, and at the role of ideology in this process. Hereby we position ourselves in the discussion between those who argue that affective polarization finds its root more strongly in group attachments vs. those who argue that it is mostly rooted in ideological differences. We conduct our study in the context of the highly fragmented multi-party system of Belgium which enables us to analytically disentangle party label cues from ideological distance. Our findings demonstrate that affective polarization is largely rooted in ideological differences between party electorates in Belgium. Additionally, we find that this particularly holds for citizens who are more ideologically invested, namely those with higher political interest and more extreme ideological views.