Description: The two basic considerations in a pension plan valuation are the choice of actuarial cost methods and actuarial assumptions. This paper deals with the assumptions. The concern in this regard is what actuaries are doing and why. There are explicit criteria why particular assumptions are chosen, and these have often been discussed in the pension literature. However, there also are implicit criteria, which, while seldom discussed in the literature, can dominate the valuation. The goal of this paper is to quantify some of these criteria, and thereby provide a basis for further discussion and research.