Chapter 4, where the author derives his failure theory, is the most important chapter of the book. The general isotropic failure behavior is determined by the spectrum of T/C values, which captures the entire range from brittle to ductile behavior between T/C = 0 and T/C = 1. The theory is based on an expansion of the elastic energy in terms of the first and second stress invariants. The relevant constants are determined in terms of T/C by considering appropriate limit cases. An elegant constitutive equation emerges in terms of the principal stresses. In principal stress space, the geometric form of this fracture criterion is that of a paraboloid. In the limit of perfect ductility, at T/C = 1, the expression reduces to the Mises criterion. On the brittle side (i.e., T/C < 0.5), additional considerations have been introduced, related to failure due to fracture. Here, it is assumed that, in a homogeneous material, cracks generate and propagate normal to the direction of maximum normal stress. The proposed additional condition is that the largest principal stress should be smaller than T. Whichever of the two failure criteria—the polynomial invariants form or the fracture mode form—is the most limiting is then the controlling failure condition at that stress state. For T/C < 0.5, the planes defining the fracture condition cut slices out of the paraboloid. Cases corresponding to the failure paraboloid sliced by the fracture failure planes are shown and discussed for widely different classes of materials in Chapter 5. Chapter 6 presents comparisons of the new theory with three sets of experimental data. It is not surprising that good agreement is found with the data for ductile metals obtained by Taylor and Quinney, since these data already showed good agreement with the Mises criterion but not with the Coulomb–Mohr and the Tresca criteria. Good agreement is also obtained for biaxial failure data on iron and for triaxial failure data for Blair dolomite. The Coulomb–Mohr criterion gives poor comparisons for the latter two sets of experimental data. The reviewer hopes that further experimental validation of the new theory will be forthcoming.