Definition: Contrariety is the mutual resistance of certain things due to their divergent ends.
Clarification: just as some sense objects are concordant with others, some are contrary to others, like whiteness and blackness, hot and cold, heavy and light, or like sensual goodness and badness in the sensual nature of concrete sense objects. There is also contrariety between sensual and intellectual things, like between the body and the soul by reason of visibility and invisibility, corruption and incorruptibility, and between intellectual and intellectual things, like willingness and unwillingness, understanding and ignoring and so forth.
Contrariety exists in two ways: real and objective. Real contrariety is found for instance between fire and water, air and earth in the same elemented subject, or between knowing and ignoring when in doubt, and between love and hate etc. Objective contrariety exists, for instance, between being and non being, something and nothing, or between fire and water in distinct subjects that do not resist each other; in the opposite sense, the same is understood about concordance.
Contrariety is a necessary principle of this Art that enables the artist to know the conditions of one contrary thing through those of another one opposed to it and vice versa, and to ascend to the knowledge of supreme contrariety against supreme concordance. Supreme contrariety is what opposes supreme concordance in the beginning and middle and impedes the good, great end of supreme concordance. There is also lesser contrariety, as between fire and water etc., and there is concordance in generation and contrariety in corruption, and so forth.
Nature: The fullness and nature of contrariety consist in the accidental opponent, the opposed and the opposition between them.
Without contrariety, beings could never decay, pass from being to non being, return from act to potentiality, or part if they are joined. It is the essence without which no being could oppose anything, and without which knowable pairs of opposites would elude our knowledge when considered in terms of majority and minority.