The basic question of the longer work that volume one introduces is a deceptively simple one: What sorts of conduct may the state rightly make criminal? Philosophers have attempted to answer this question by proposing what I call "liberty-limiting principles" (or equivalently, "coercion-legitimizing principles") which state that a given type of consideration is always a morally relevant reason in support of penal legislation even if other reasons may in the circumstances outweigh it.
