/summa/FS/FSIII/FS_Q36:
We must now consider the causes of sorrow: under which head there are four points of inquiry:
(1) Whether sorrow is caused by the loss of a good or rather by the presence of an evil?
(2) Whether desire is a cause of sorrow?
(3) Whether the craving for unity is a cause of sorrow?
(4) Whether an irresistible power is a cause of sorrow?