ove (A. 2, ad 3), man, on account of
sin, is compared to the beasts. Now it is lawful for any private
individual to kill a wild beast, especially if it be harmful.
Therefore for the same reason, it is lawful for any private
individual to kill a man who has sinned.

Obj. 3: Further, a man, though a private individual, deserves praise
for doing what is useful for the common good. Now the slaying of
evildoers is useful for the common good, as stated above (A. 2).
Therefore it is deserving of praise if even private individuals kill
evil-doers.

_On the contrary,_ Augustine says (De Civ. Dei i) [*Can. Quicumque
percutit, caus. xxiii, qu. 8]: "A man who, without exercising public
authority, kills an evil-doer, shall be judged guilty of murder, and
all the more, since he has dared to usurp a power which God has not
given him."

_I answer that,_ As stated above (A. 2), it is lawful to kill an
evildoer in so far as it is directed to the welfare of the whole
community, so that it belongs to him alone who has charge of the
community's welfare. Thus it belongs to a physician to cut off a
decayed limb, when he has been entrusted with the care of the health
of the whole body. Now the care of the common good is entrusted to
persons of rank having public authority: wherefore they alone, and
not private individuals, can lawfully put evildoers to death.

Reply Obj. 1: The person by whose authority a thing is done really
does the thing as Dionysius declares (Coel. Hier. iii). Hence
according to Augustine (De Civ. Dei i, 21), "He slays not who owes
his service to one who commands him, even as a sword is merely the
instrument to him that wields it." Wherefore those who, at the Lord's
command, slew their neighbors and friends, would seem not to have
done this themselves, but rather He by whose authority they acted
thus: just as a soldier slays the foe by the authority of his
sovereign, and the executioner slays the robber by the authority of
the judge.

Reply Obj. 2: A beast is by nature distinct from man, wherefore in
the case of a wild beast there is no need for an authority to kill
it; whereas, in the case of domestic animals, such authority is
required, not for their sake, but on account of the owner's loss. On
the other hand a man who has sinned is not by nature distinct from
good men; hence a public authority is requisite in order to condemn
him to death for the common good.

Reply Obj. 3: It is lawful for any private individu