a constituent part. Moreover, defining rest as the absence of motion is no more warranted than the reverse. Thus, either both are absences—which is false by common agreement—or they must both be positive realities.”

One may respond as follows:

The contrariety between motion and rest is of the same kind as that between life and death, knowledge and ignorance, ability and inability, blackness and whiteness, blindness and sight, sweetness and sourness, and other such attributes, whether both are positive or one is positive and the other privative. It is not of the same kind as the opposition between two independently subsisting things, such as a black object and a white object. Contrariety applies only to two things that alternate in a single subject, as the affirmationist theologians have said:

“Contraries are any two properties whose very natures make it impossible for them to coexist in a single subject in the same respect.”

Unless the two properties have a single subject in which to inhere, there is no contrariety. Motion and rest alternate in a single subject, either as two colours or two tastes succeed one another, or as knowledge, sight, and hearing alternate with their absence. How, then, could one be identical in nature to the other, differing from it only in an incidental attribute?

In short, if motion and rest are both positive realities, they are two accidents; if one is a positive reality, then one is an accident and the other is the absence of that accident. On either assumption, neither subsists independently. They therefore cannot be likened to bodies, such as a black object and a white object, a tall person and a short person, or a knowledgeable person and an ignorant person. Rather, they must be likened to accidents and their absence, such as blackness and whiteness, knowledge and the absence of knowledge, and the like.