returning to the weak monotonicity assumption, which assumes that the utility function always runs in one direction, the utility of a marginal complier would be similar to the utility of a never-taker on one end, and that of an always-taker on the other end. the always-takers will have the same untreated potential outcomes as the compliers, which is its maximum untreated potential outcome. again, this is based on the underlying utility model linking the subgroups, which assumes that the utility function of an always-taker would not be lower than the utility function of a complier. the same logic would apply to the never-takers, who are assumed to have a utility function that will always be lower than that of a complier.