Again, concupiscence may signify a natural proneness found in our rational appetite, that is, a spontaneous tendency in the will to desire what is pleasurable to the senses. By reason of the intimate union of sentient nature and rational will in the unity of our being, the will is affected by the promptings of our senient nature and is prone to identify itself pleasurably with these. In these ways concupiscence is a material consequence of original sin, inasmuch as through the loss of original justice and integrity, and the absence of their moderating influence in curbing desire, we are now prone to covet inordinate pleasure, as a horse deprived of its bridle will tend to go astray, an event which the bridle would have prevented. 23
The example of the horse and bridle quoted by Scotus gives us an accurate picture of the nature of concupiscence as he understood it. There is no question of a deteriorated physical condition of our nature as a result of inherited concupiscence, but of changed circumstances under which our will now functions. The fundamental proneness of our lower appetites toward their own good was always there; it is a part of the psychological structure and functioning of normal human nature. What has changed is that the "bridle has been removed.” In other words, because of Adam’s sin we are now deprived of the moderating check of original integrity. In consequence, we now have a state of rebellion and moral struggle, whereas in paradise there existed a holy state of harmony.
To sum up: for Scotus, original sin is a moral defect found in the soul of man. Its cause is a moral demeriting cause. In a word, original sin consists in the absence of
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