Party competition is held around political conflicts and identities. And, as Riker’s heresthetics’ theory shows, depending on which are those issues the competition can take different directions. That means that, no good understanding of the electoral dynamics can be reached without understanding the processes by which new issues appear in the agenda, the role parties in determining them and the ways in which voters respond to changes on it. However, and despite some punctual exceptions no big effort has been made to understand the process in a comprehensive and dynamic way. This paper whether the dimensionality of parties’ offer changes and whether it does so for strategic reasons. First, it presents the empirical strategy and the measurements. Then it moves to explain changes on the dimensionality of the political offer, its evolution and its main features. Finally, it moves to the study of the reasons that explain those changes
