One of the key questions in studies of voting behaviour is how voters rank or form preferences between parties. In this article, we study how the set of alternatives provided by the party system affects voters' preference formation. More specifically, we study whether the proximity of a political party in the conventional left-right dimension is a better predictor of a voter's preference when parties offer distinct positions than when parties' positions are close to each other. Using the data provided by the Comparative Study of Electoral Systems, we find convincing evidence that supports the argument that proximity is more salient in polarized party systems compared with party systems where polarization is low.