The relaxed work from a history H' to a history H is defined as the minimum work required to approach H via a sequence of continuations of H'. I prove three basic properties of the relaxed work: subadditivity, lower semicontinuity with respect to H for fixed H', and two dissipation inequalities. The proofs require the assumption that the relaxed work be bounded from below. It is proved that this assumption is equivalent to a number of statements of thermodynamic type that, in other thermodynamical contexts, need not be equivalent. The surprising coincidence of statements of a different nature suggests, at least for linear viscoelasticity, the idea of a single dissipation postulate. A systematic deduction of a number of consequences of this postulate forms the object of the final part of the paper.