 One challenge for all of these accounts is to identify an attribute or attributes that can explain, or at least be reconciled with, the threshold and range features of the prevailing concept of moral status. The difficulty presented by a threshold is that it imposes moral discontinuity over psychologically continuous attributes. In contrast to the possession of a soul, for example, practical rationality, moral responsibility, and most other individual attributes claimed by contemporary accounts to ground moral status, appear to come in degrees. Looking at the development of an infant, the acquisition of these attributes appears to be gradual, even if its pace is uneven. And yet our judgment of moral status appears categorical—an individual either has full moral status or lacks it. The categorical character of moral status is also clear above the threshold. We do not think that the more highly intelligent, more deeply self-conscious, or more fully autonomous among us have a higher moral status than the rest, even those near the edge. The challenge of justifying this range feature of full moral status is closely related to the challenge of justifying the threshold—why should differences above the threshold be morally insignificant when the threshold itself is so significant?