 Berkovitz, Frigg and Kronz (2006) discuss this problem and argue that EH is best understood as a hierarchy of random behaviour if randomness is explicated in terms of unpredictability, where unpredictability is accounted for in terms of probabilistic relevance. Different patterns of probabilistic relevance, in turn, are spelled out in terms of different types of decay of correlation between a system’s states at different times. Let us introduce these elements one at a time.