Affection is in one sense spoken of a quality in virtue of which a body can be altered, such as white and black, sweet and bitter, heaviness and lightness, and the like; in another every effect and alteration that already comes about with regard to these, such as being white or black or cold or hot. This so called affection is a certain impermanent change in virtue either of the soul or the body. Of the former it is the injurious alterations and changes that are called affections to a greater extent — either in virtue of the soul or in virtue of the body — especially those that are concerned with injurious and disagreeable circumstances, such as sickly annoyances and disagreeable annoyances that are mistaken. Moreover, an extreme sadness or disaster are called affection.
Bibliography: Aristotle, Metaphysics (1022b.15 to 1022b.21), Alexander of Aphrodisias in Metaphysics
Translation, text editing: George Kotsalis