The Summa Theologiae is Thomas Aquinas' undisputed masterwork, and it includes his thoughts on the elemental forces in human life. Feelings such as love, hatred, pleasure, pain, hope and despair were described by Aquinas as 'passions', representing the different ways in which happiness could be affected. But what causes the passions? What impact do they have on the person who suffers them? Can they be shaped and reshaped in order to better promote...