Publisher Summary8.1 CAUSALITY, MODULARITY, AND TREE STRUCTURES8.2 STRUCTURING THE OBSERVABLES8.3 LEARNING HIDDEN CAUSES8.4 BIBLIOGRAPHICAL AND HISTORICAL REMARKSAppendix 8-A Proof of Theorems 1 and 2Appendix 8-B Conditions for Star-Decomposability (After Lazarfeld [1966])