In some ways, the e?ect of achieving understanding is to reverse completely our initial attitude of mind. For everyone starts (as we have said) by being perplexed by some fact or other: for instance... the fact that the diagonal of a square is incommensurable with the side. Anyone who has not yet seen why the side and the diagonal have no common unit regards this as quite extra- dinary. But one ends up in the opposite frame of mind... for nothing would so much ?abbergast a mathematician as if the diagonal and side of a square were to become commensurable . Aristotele] This is the ?rst volume...

3 Domenico Delli Gatti!, Mauro GallegatF, Alan P. Kirman ! ITEMQ, Catholic University, Milan, Italy 2 MET, University of Teramo, Italy 3 GREQAM, Universite d'Aix-Marseille, Ecole des Hautes Etudes en Sciences Sociales, and Institut Universitaire de France The economics of heterogeneity This volume contains a set of papers which pursue the aim of examining how the properties of aggregate economic variables are influenced by the actions and interactions of individuals. This has been the central theme of a series of workshops held at the University of Ancona, Italy, since 1996, whose general...

In some ways, the e?ect of achieving understanding is to reverse completely our initial attitude of mind. For everyone starts (as we have said) by being perplexed by some fact or other: for instance... the fact that the diagonal of a square is incommensurable with the side. Anyone who has not yet seen why the side and the diagonal have no common unit regards this as quite extra- dinary. But one ends up in the opposite frame of mind... for nothing would so much ?abbergast a mathematician as if the diagonal and side of a square were to become commensurable . Aristotele] This is the ?rst volume...