Objection 1. It would seem that Damascene's (De Fide Orth. ii, 14) division of sorrow into four species is incorrect; viz. into "torpor, distress," which Gregory of Nyssa [Nemesius, De Nat. Hom. xix.] calls "anxiety,"--"pity," and "envy." For sorrow is contrary to pleasure. But there are not several species of pleasure. Therefore it is incorrect to assign different species of sorrow.
Objection 2. Further, "Repentance" is a species of sorrow; and so are "indignation" and "jealousy," as the Philosopher states (Rhet. ii, 9,11). But these are not included in the above species. Therefore this division is insufficient.
Objection 3. Further, the members of a division should be things that are opposed to one another. But these species are not opposed to one another. For according to Gregory [Nemesius, De Nat. Hom. xix.] "torpor is sorrow depriving of speech; anxiety is the sorrow that weighs down; envy is sorrow for another's good; pity is sorrow for another's wrongs." But it is possible for one to sorrow for another's wrongs, and for another's good, and at the same time to be weighed down inwardly, and outwardly to be speechless. Therefore this division is correct.
On the contrary, stands the twofold authority of Gregory of Nyssa [Nemesius] and of Damascene.
I answer that, It belongs to the notion of a species that it is something added to the genus. But a thing can be added to a genus in two ways. First, as something belonging of itself to the genus, and virtually contained therein: thus "rational" is added to "animal." Such an addition makes true species of a genus: as the Philosopher says (Metaph. vii, 12; viii, 2,3). But, secondly, a thing may be added to a genus, that is, as it were, foreign to the notion conveyed by that genus: thus "white" or something of the kind may be added to "animal." Such an addition does not make true species of the genus, according to the usual sense in which we speak of genera and species. But sometimes a thing is said to be a species of a certain genus, through having something foreign to that genus indeed, but to which the notion of that genus is applicable: thus a live coal or a flame is said to be a species of fire, because in each of them the nature of fire is applied to a foreign matter. In like manner we speak of astronomy and perspective as being species of mathematics, inasmuch as the principles of mathematics are applied to natural matter.
In accordance with this manner of speaking, the species of sorrow are reckoned by an application of the notion of sorrow to something foreign to it. This foreign matter may be taken on the part of the cause or the object, or of the effect. For the proper object of sorrow is "one's own evil." Hence sorrow may be concerned for an object foreign to it either through one's being sorry for an evil that is not one's own; and thus we have "pity" which is sorrow for another's evil, considered, however, as one's own: or through one's being sorry for something that is neither evil nor one's own, but another's good, considered, however, as one's own evil: and thus we have "envy." The proper effect of sorrow consists in a certain "flight of the appetite." Wherefore the foreign element in the effect of sorrow, may be taken so as to affect the first part only, by excluding flight: and thus we have "anxiety" which weighs on the mind, so as to make escape seem impossible: hence it is also called "perplexity." If, however, the mind be weighed down so much, that even the limbs become motionless, which belongs to "torpor," then we have the foreign element affecting both, since there is neither flight, nor is the effect in the appetite. And the reason why torpor especially is said to deprive one of speech is because of all the external movements the voice is the best expression of the inward thought and desire, not only in men, but also in other animals, as is stated in Polit. i, 1.
Reply to Objection 1. Pleasure is caused by good, which has only one meaning: and so pleasure is not divided into several species as sorrow is; for the latter is caused by evil, which "happens in many ways," as Dionysius says (Div. Nom. iv).
Reply to Objection 2. Repentance is for one's own evil, which is the proper object of sorrow: wherefore it does not belong to these species. Jealousy and indignation are included in envy, as we shall explain later (II-II, 36, 2).
Reply to Objection 3. This division is not according to opposite species; but according to the diversity of foreign matter to which the notion of sorrow is applied, as stated above.
Source: Summa Theologica (New Advent)