SLOTH. - (From the Greek ἀκῆδία = carelessness, from α privative and κῆδομα). Commonly the term a. is used to indicate that vice by which one neglects to do good; hence a. is properly "weariness or tedium of doing good" and "negligence in what pertains to the things of God and of the soul." It is therefore opposed to zeal and especially to spiritual alacrity; although it also denotes an inert indifference and denial of any idealism, for which it is also popularly called laziness.
For spiritual writers a. has the sense of "discouragement of a soul that believes itself incapable of overcoming certain difficulties," and is therefore for that soul a cause of sadness and despondency. Theologians consider it under two aspects: as a passion and as a vice or sin. a) As a passion it is a manifestation of sadness and despondency in the face of the effort that must be sustained in any kind of activity. Such a passion does not constitute a merely individual bad tendency, but is common to all and to each one, as an inclination to quiet and inertia that attempt to dissuade man from troubling himself to practice this or that virtue. Nevertheless, even as a passion, a. almost always takes on an individual character; whence we see that it manifests itself with countless gradations. b) As a fault or sin it is not only a passion having its seat in the sensitive appetite, but also an effect of the will itself: which, however, is ordinarily seconded also by some sensitive passion. In this sense St. Thomas (Sum. Theol. 2°-3°c, q. 35, a. 1) defines a. as: a displeasure at spiritual good, insofar as this is divine good; that is to say: a sadness that is born in us by reason of having to put into practice what pertains to the service of God. Thus a. comes to be one of the seven capital vices (the seventh), which is opposed to charity toward God.
This vice can be considered: 1° in general with respect to the practice of every virtue; and it is a slowing of the spirit, a boredom, a torpor that leads to negligence in the exercise of individual virtues, to each of which some fatigue is necessarily attached; 2° in particular, with respect to spiritual goods; and then it is a tedium of friendship and divine grace. Under the first aspect it can be a mortal or a venial sin,
accordingly as through it the precept of an
action gravely or lightly obligatory is violated; under the
second aspect, if it is voluntary, it is always a mortal
sin, because it gravely repugns to charity toward God.

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Igino Tarocchi