/summa/FS/FSIII/FS_Q25:
We must now consider the order of the passions to one another: and under this head there are four points of inquiry:
(1) The relation of the irascible passions to the concupiscible passions;
(2) The relation of the concupiscible passions to one another;
(3) The relation of the irascible passions to one another;
(4) The four principal passions.