Whether It Is Lawful to Swear?
Objection 1: It would seem that it is not lawful to swear. Nothing
forbidden in the Divine Law is lawful. Now swearing is forbidden
(Matt. 5:34), "But I say to you not to swear at all"; and (James
5:12), "Above all things, my brethren, swear not." Therefore swearing
is unlawful.
Obj. 2: Further, whatever comes from an evil seems to be unlawful,
because according to Matt. 7:18, "neither can an evil tree bring
forth good fruit." Now swearing comes from an evil, for it is written
(Matt. 5:37): "But let your speech be: Yea, yea: No, no. And that
which is over and above these is of evil." Therefore swearing is
apparently unlawful.
Obj. 3: Further, to seek a sign of Divine Providence is to tempt God,
and this is altogether unlawful, according to Deut. 6:16, "Thou shalt
not tempt the Lord thy God." Now he that swears seems to seek a sign
of Divine Providence, since he asks God to bear witness, and this
must be by some evident effect. Therefore it seems that swearing is
altogether unlawful.
_On the contrary,_ It is written (Deut. 6:13): "Thou shalt fear the
Lord thy God . . . and shalt swear by His name."
_I answer that,_ Nothing prevents a thing being good in itself, and
yet becoming a source of evil to one who makes use thereof
unbecomingly: thus to receive the Eucharist is good, and yet he that
receives it "unworthily, eateth and drinketh judgment to himself" (1
Cor. 11:29). Accordingly in answer to the question in point it must
be stated that an oath is in itself lawful and commendable. This is
proved from its origin and from its end. From its origin, because
swearing owes its introduction to the faith whereby man believes that
God possesses unerring truth and universal knowledge and foresight of
all things: and from its end, since oaths are employed in order to
justify men, and to put an end to controversy (Heb. 6:16).
Yet an oath becomes a source of evil to him that makes evil use of
it, that is who employs it without necessity and due caution. For if
a man calls God as witness, for some trifling reason, it would
seemingly prove him to have but little reverence for God, since he
would not treat even a good man in this manner. Moreover, he is in
danger of committing perjury, because man easily offends in words,
according to James 3:2, "If any man offend not in word, the same is a
perfect man." Wherefore it is written (Ecclus. 23:9): "Let not thy
mouth be accustomed to swearing, for in it there are many falls."
Reply Obj. 1: Jerome, commenting on Matt. 5:34, says: "Observe that
our Saviour forbade us to swear, not by God, but by heaven and earth.
For it is known that the Jews have this most evil custom of swearing
by the elements." Yet this answer does not suffice, because James
adds, "nor by any other oath." Wherefore we must reply that, as
Augustine states (De Mendacio xv), "when the Apostle employs an oath
in his epistles, he shows how we are to understand the saying, 'I say
to you, not to swear at all'; lest, to wit, swearing lead us to swear
easily and from swearing easily, we contract the habit, and, from
swearing habitually, we fall into perjury. Hence we find that he
swore only when writing, because thought brings caution and avoids
hasty words."
Reply Obj. 2: According to Augustine (De Serm. Dom. in Monte i. 17):
"If you have to swear, note that the necessity arises from the
infirmity of those whom you convince, which infirmity is indeed an
evil. Accordingly He did not say: 'That which is over and above is
evil,' but 'is of evil.' For you do no evil; since you make good use
of swearing, by persuading another to a useful purpose: yet it 'comes
of the evil' of the person by whose infirmity you are forced to
swear."
Reply Obj. 3: He who swears tempts not God, because it is not without
usefulness and necessity that he implores the Divine assistance.
Moreover, he does not expose himself to danger, if God be unwilling
to bear witness there and then: for He certainly will bear witness at
some future time, when He "will bring to light the hidden things of
darkness, and will make manifest the counsels of hearts" (1 Cor.
4:5). And this witness will be lacking to none who swears, neither
for nor against him.
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