 Reichenbach offers three accounts of the direction of time. The first is that the direction of time in a region of space-time is the most common direction of increasing entropy among multiple nearly isolated systems in that region. The idea, as Reichenbach notes, is Boltzmann’s. The second answer is that the direction of time is that in which causal events turn high entropy systems into low entropy, ordered systems. In the reverse direction of the same process, he says, from low entropy to high entropy, the sequence of events is not causal but “purposive.” Thus stepping in sand makes a shape (low entropy) from a flat surface (high entropy). The reverse process, removing the foot from the sand followed by the foot impression filling with sand is not causal, but purposive. We do not pretend to understand this argument. The third argument intends to produce a direction of time from causal directions inferred from macrostatistics. This is the perhaps the aspect of the book most often discussed, and it both breaks new ground and occasionally stumbles in the furrows. 