 The question of how to characterise chaos has been controversially discussed ever since the inception of chaos theory; for a survey see Smith (1998, Ch. 10). An important family of approaches defines chaos using EH. Belot and Earman (1997, 155) state that being strong mixing is a necessary condition and being a K-system is a sufficient condition for a system to be chaotic. The view that being a K-system is the mark of chaos and that any lower degree of randomness is not chaotic is frequently motivated by two ideas. The first is the idea that chaotic behaviour involves dynamical instability in the form of exponential divergence of nearby trajectories. Thus, since a system involves an exponential divergence of nearby trajectories only if it is a K-system, it is concluded that (merely) ergodic and mixing systems are not chaotic whereas K- and B-systems are. It is noteworthy, however, that SM is compatible with there being polynomial divergence of nearby trajectories and that such divergence sometimes exceeds exponential divergence in the short run. Thus, if chaos is to be closely associated with the rate of divergence of nearby trajectories, there seems to be no good reason to deny that SM systems exhibit chaotic behaviour.