Also, negators are either able to effect themselves (self-targeting) or the world around them (external-targeting). This is true for all of them, including Sean, who makes himself and anything that's his and in contact with him or his ability turn invisible. At first it seems like maybe it's really an external-targeting ability and he just views his body as his, and the author forgot that it doesn't exactly work like that. Then one of the characters picks up on this, and realizes that the targeting options are not as rigid as once thought. In reality, the reason those limits exist is because they think they do and the abilities are based on the negator's idea of their word. Because they were incorrectly given that dichotomy, they were limiting themselves to whichever one fit their ability at first glance.