Time Maudlin starts by distinguishing and characterizing three different classes of explanations of thermodynamic phenomena previously studied in the seminar (appeals to symmetry principles, to random walks in the phase space, or to features of the actual micro-dynamics of isolated systems). He explains the various ways in which the standard measure over phase space comes into play in these explanations. David Albert then examines the various ways in which one might justify appealing to this standard measure; both Maudlin and Albert reject justifications that appeal to principles of indifference, but disagree on whether the measure is to be justified solely on empirical grounds (David) or by its natural character (Tim). In the last part of the class, David starts explaining the reversibility objections raised against Maxwell’s and Boltzmann’s arguments.