Now the cause of the appetitive movement, on the part of the end, is the object of that movement.  And thus, it has been said above (A. 1) that the cause of pain or sorrow is a present evil.  On the other hand, the cause, by way of principle, of that movement, is the inward inclination of the appetite; which inclination regards, first of all, the good, and in consequence, the rejection of a contrary evil.  Hence the first principle of this appetitive movement is love, which is the first inclination of the appetite towards the possession of good:  while the second principle is hatred, which is the first inclination of the appetite towards the avoidance of evil.  But since concupiscence or desire is the first effect of love, which gives rise to the greatest pleasure, as stated above (Q. 32, A. 6); hence it is that Augustine often speaks of desire or concupiscence in the sense of love, as was also stated (Q. 30, A. 2, ad 2):  and in this sense he says that desire is the universal cause of sorrow.  Sometimes, however, desire taken in its proper sense, is the cause of sorrow.  Because whatever hinders a movement from reaching its end is contrary to that movement.  Now that which is contrary to the movement of the appetite, is a cause of sorrow.  Consequently, desire becomes a cause of sorrow, in so far as we sorrow for the delay of a desired good, or for its entire removal.  But it cannot be a universal cause of sorrow:  since we sorrow more for the loss of present good, in which we have already taken pleasure, than for the withdrawal of future good which we desire to have.

Reply Obj. 1:  The inclination of the appetite to the possession of good causes the inclination of the appetite to fly from evil, as stated above.  And hence it is that the appetitive movements that regard good, are reckoned as causing the appetitive movements that regard evil.

Reply Obj. 2:  That which is desired, though really future, is, nevertheless, in a way, present, inasmuch as it is hoped for.  Or we may say that although the desired good itself is future, yet the hindrance is reckoned as present, and so gives rise to sorrow.

Reply Obj. 3:  Desire gives pleasure, so long as there is hope of obtaining that which is desired.  But, when hope is removed through the presence of an obstacle, desire causes sorrow. ________________________

THIRD ARTICLE [I-II, Q. 36, Art. 3]

Whether the Craving for Unity Is a Cause of Sorrow?

Objection 1:  It would seem that the craving for unity is not a cause of sorrow.  For the Philosopher says (Ethic. x, 3) that “this opinion,” which held repletion to be the cause of pleasure, and division [Aristotle wrote _endeian_, ‘want’; St. Thomas, in the Latin version, read ‘incisionem’; should he have read ’indigentiam’?], the cause of sorrow, “seems to have originated in pains and pleasures connected with food.”  But not every pleasure or sorrow is of this kind.  Therefore the craving for unity is not the universal cause of sorrow; since repletion pertains to unity, and division is the cause of multitude.