reviler injuring a man's honor, the
backbiter injuring his good name.

Reply Obj. 1: In involuntary commutations, to which are reduced all
injuries inflicted on our neighbor, whether by word or by deed, the
kind of sin is differentiated by the circumstances "secretly" and
"openly," because involuntariness itself is diversified by violence
and by ignorance, as stated above (Q. 65, A. 4; I-II, Q. 6, AA. 5, 8).

Reply Obj. 2: The words of a backbiter are said to be secret, not
altogether, but in relation to the person of whom they are said,
because they are uttered in his absence and without his knowledge. On
the other hand, the reviler speaks against a man to his face.
Wherefore if a man speaks ill of another in the presence of several,
it is a case of backbiting if he be absent, but of reviling if he
alone be present: although if a man speak ill of an absent person to
one man alone, he destroys his good name not altogether but partly.

Reply Obj. 3: A man is said to backbite (_detrahere_) another, not
because he detracts from the truth, but because he lessens his good
name. This is done sometimes directly, sometimes indirectly.
Directly, in four ways: first, by saying that which is false about
him; secondly, by stating his sin to be greater than it is; thirdly,
by revealing something unknown about him; fourthly, by ascribing his
good deeds to a bad intention. Indirectly, this is done either by
gainsaying his good, or by maliciously concealing it, or by
diminishing it.
_______________________

SECOND ARTICLE [II-II, Q. 73, Art. 2]

Whether Backbiting Is a Mortal Sin?

Objection 1: It would seem that backbiting is not a mortal sin. For
no act of virtue is a mortal sin. Now, to reveal an unknown sin,
which pertains to backbiting, as stated above (A. 1, ad 3), is an act
of the virtue of charity, whereby a man denounces his brother's sin
in order that he may amend: or else it is an act of justice, whereby
a man accuses his brother. Therefore backbiting is not a mortal sin.

Obj. 2: Further, a gloss on Prov. 24:21, "Have nothing to do with
detractors," says: "The whole human race is in peril from this vice."
But no mortal sin is to be found in the whole of mankind, since many
refrain from mortal sin: whereas they are venial sins that are found
in all. Therefore backbiting is a venial sin.

Obj. 3: Further, Augustine in a homily _on the Fire of Purgatory_
[*Serm. civ in the appendix to St. Augustine's work] reckons i