Welcome home, beadfurd. Yeah, the hortatory subjunctive is a politer way of telling somebody what to do than is the plain ole imperative. I'm trying to figure out how it works in this example, though. Maybe it's just the common, garden variety subjunctive and no exhorting a tall. But, hey. What do I know? Parboly sommun'll come along and point out the obvious and you'll be vindicated.