Modigliani and Miller's basic conceptual device, homogeneous "risk classes" (see appendix A), had no empirical referent, argued Durand: "To the practically minded, it is unthinkable to postulate the existence of two or more separate and independent corporations with income streams that can fluctuate at random and yet be perfectly correlated from now until doomsday." Modigliani and Miller had started "with a perfect market in a perfect world," wrote Durand.

Donald MacKenzie, An Engine, Not a Camera, loc. 195