Sloth, acedia, is the most easily misunderstood of the seven, because the English word suggests mere laziness and the Latin term does not mean that. Akedia in Evagrius is the noonday demon of Psalm 91, the listlessness that overtakes a monk in the middle of the day, when the cell becomes unbearable, the hours crawl, the work seems pointless and the life seems a mistake; it is a spiritual condition compounded of boredom, restlessness and despair rather than a reluctance to work, and Evagrius describes it with a precision that has struck many modern readers as clinical. Gregory merged tristitia, sorrow, into it when he reduced the eight to seven. Aquinas defines it as sorrow at the divine good, a sadness that shrinks from the effort the spiritual life requires, and classes it as a sin against the joy that belongs to charity.
Cassian, following Evagrius, had treated tristitia, worldly sorrow or despondency, as a distinct affliction from acedia, drawing on Paul's distinction at 2 Corinthians 7:10 between a godly sorrow that produces repentance and a worldly sorrow that produces death; when Gregory folded tristitia into acedia to reach his sevenfold scheme, later commentators note that some of the sharper psychological distinctions the desert fathers had drawn between the two states were correspondingly lost, one reason modern readers recovering Evagrius's fuller eightfold analysis have found it more clinically precise than Gregory's more compressed later synthesis.