Acedia, the shunning of difficult good, is a 'capital sin', that is, it serves as the fountainhead of other sins, which are called its 'daughters'. Aquinas addresses two lists of daughters of sloth, one by Isidore and one by Gregory the Great.
Isidore (De Summo Bono ii, 37) distinguishes between sorrow and sloth. In sorrow a man shuns difficult good because he finds it difficult or burdensome; in sloth he shuns it because he is overly inclined to rest and repose. From sorrow come the following:
spite, faint-heartedness, bitterness, despair
From sloth come the following:
idleness, drowsiness, uneasiness of the mind, restlessness of the body, instability, loquacity, curiosity
Aquinas will reject the view, found in Isidore and Cassian (De Instit. Caenob. x, 1), that these are distinct vices, and so will treat them as one list.
Gregory, whose list is the one from which Aquinas will primarily draw, lists the daughters of sloth as follows (Moral. xxxi, 45):
malice, spite, faint-heartedness, despair, sluggishness in regard to the commandments, wandering of the mind after unlawful things
Aquinas defends Gregory's listing by distinguishing two steps by which someone fails with regard to some unpleasant good: first he comes to withdraw from, or shun, the good itself, and then he comes to pass it over in favor of something more pleasant. Likewise, when someone shuns the unpleasant, there are two steps: first he begins to avoid it, then he begins to struggle actively against it. "Despair" is then the avoidance of spiritual good considered as an end in itself; "faint-heartedness" is the avoidance of spiritual good that is the reasonable means to the end in matters of genuine difficulty; "sluggishness about the commandments" is the avoidance of spiritual good that is the reasonable means to the end in matters of common righteousness. These are all cases where we shun spiritual good by trying simply to avoid it. When our vice becomes aggravated, we move on to struggling against it. When our struggle against unpleasant spiritual good leads us to attack those people who lead others to that good, we have descended into "spite," and "malice" arises when we descend to detesting the good itself. This leaves the last step by which the vice of sloth generates other vices, namely, where we pass over the difficult or unpleasant good in favor of something easy and pleasant, such as when people devote themselves to fleshly pleasures because they find no joy in spiritual or intellectual things. This is "wandering after unlawful things."
The Combined List
How are the two lists related to each other? Thomas argues that the elements on Isidore's lists (both the list for sorrow and the list for sloth) reduce to elements on Gregory's list. This leads us to the full list of the daughters of sloth:
Sloth involves shunning the unpleasant good:
A. By avoiding it
1. Considered as an end: despair
2. Considered as a means in difficult matters: faint-heartedness
3. Considered as a means in matters of common righteousness: sluggishness
3a. By omitting it altogether: idleness
3b. By pursuing it negligently: drowsiness
B. By struggling against it
1. Indignation against those who lead us to it: spite
2. Detestation of the good itself: malice
C. By passing on to more pleasant things
1. In matters of intellect: uneasiness of mind
2. In matters of imagination: curiosity
3. In matters of speech: loquacity
4. In matters of physical motion: restlessness of body
5. In matters of purpose: instability
Strictly speaking, Thomas gives two different possible accounts of Isidore's "instability," not deciding between them (i.e., either in matters where the body moves from place to place or in matters of purpose). All of the five under C are various ways in which people exhibit a mental unsteadiness, a lack of dependability and self-control wherever difficulty may be involved, a pursuit of pleasant distractions rather than genuine good.
One of the interesting things about this list of the daughters of sloth is how easily it could be turned into a ringing indictment and critique of our contemporary society. A modern-day Dante, looking for examples by which he might people the slothful ring of hell, would find plenty from which to choose. It is one thing, for instance, to criticize this or that move by Theresa of Calcutta; it is another, as is sometimes done, for people to try to spin every action by which she tried to exhort people to good as somehow evil. That is spite; and, what is more, it is spite that tends to malice. If an archangel were to look out on all our society, would he issue the following judgment?
This is a slothful nation, desperate and faint-hearted, idle and drowsy in pursuit of goods that are difficult, spiteful and malicious towards goods that are unpleasant, drowning itself in trivialities, in words, in frivolous and useless pursuits.
I think he might well do so. We do very little to discipline our reason so that it does not consent to "the dislike, horror and detestation of the Divine good, on account of the flesh utterly prevailing over the spirit"; without such discipline it becomes difficult to overcome the temptation when it arises. The only remedy is to chase it out by its opposite: which is charity, in its aspect of joy in the good, regardless of its difficulty or pleasantness. We need more celebration of the good for which you have to labor and sometimes toil; more celebration of it as good, as worthy even of the labor and toil required, as in some sense transfiguring that labor and toil into a worthwhile task of its own.