Commentary Purg XVI 67-78

Marco's immediate and angry response (but his anger is meant to be taken as virtuous, as the righteous indignation of the just) lays the issue bare.  'The fault is in the stars' was an earlier day's way of claiming 'the dog [or computer] ate my homework' or 'the devil made me do it.'  The celestial spheres, forming our tendencies, do incline us to various sensuous and sensual activities, but we are not forced to follow our appetites, since we have our will to direct our appetites.  The concept of free will does not receive its full exposition until Beatrice's discourse upon it in [Par V 19-84], a moment marked by heavy seriousness because this concept lies at the very core of any Christian moral assertion.  In Platonic (and Aristotelian) terms, our sensitive soul, which responds to such stimuli, is (or should be) governed by our rational soul.