Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
We must now consider irony, under which head there are two points of inquiry:
(1) Whether irony is a sin?
(2) Of its comparison with boasting.
Objection 1: It seems that irony, which consists in belittling oneself, is not a sin. For no sin arises from one's being strengthened by God: and yet this leads one to belittle oneself, according toProv. 30:1, 2: "The vision which the man spoke, with whom is God, and who being strengthened by God, abiding with him, said, I am the most foolish of men." Also it is written (Amos 7:14): "Amos answered . . . I am not a prophet." Therefore irony, whereby a man belittles himself in words, is not a sin.
Objection 2: Further, Gregory says in a letter to Augustine, bishop of the English (Regist. xii): "It is the mark of a well-disposed mind to acknowledge one's fault when one is not guilty." But all sin is inconsistent with a well-disposed mind. Therefore irony is not a sin.
Objection 3: Further, it is not a sin to shun pride. But "some belittle themselves in words, so as to avoid pride," according to the Philosopher (Ethic. iv, 7). Therefore irony is not a sin.
On the contrary, Augustine says (De Verb. Apost., Serm. xxix): "If thou liest on account of humility, if thou wert not a sinner before lying, thou hast become one by lying."
I answer that, To speak so as to belittle oneself may occur in two ways. First so as to safeguard truth, as when a man conceals the greater things in himself, but discovers and asserts lesser things of himself the presence of which in himself he perceives. To belittle oneself in this way does not belong to irony, nor is it a sin in respect of its genus, except through corruption of one of its circumstances. Secondly, a person belittles himself by forsaking the truth, for instance by ascribing to himself something mean the existence of which in himself he does not perceive, or by denying something great of himself, which nevertheless he perceives himself to possess: this pertains to irony, and is always a sin.
Reply to Objection 1: There is a twofold wisdom and a twofold folly. For there is a wisdom according to God, which has human or worldly folly annexed to it, according to 1 Cor. 3:18, "If any man among you seem to be wise in this world, let him become a fool that he may be wise." But there is another wisdom that is worldly, which as the same text goes on to say, "is foolishness with God." Accordingly, he that is strengthened by God acknowledges himself to be most foolish in the estimation of men, because, to wit, he despises human things, which human wisdom seeks. Hence the text quoted continues, "and the wisdom of men is not with me," and farther on, "and I have known the science of the saints" [*Vulg.: 'and I have not known the science of the saints'].
It may also be replied that "the wisdom of men" is that which is acquired by human reason, while the "wisdom of the saints" is that which is received by divine inspiration.
Amos denied that he was a prophet by birth, since, to wit, he was not of the race of prophets: hence the text goes on, "nor am I the son of a prophet."
Reply to Objection 2: It belongs to a well-disposed mind that a man tend to perfect righteousness, and consequently deem himself guilty, not only if he fall short of common righteousness, which is truly a sin, but also if he fall short of perfect righteousness, which sometimes is not a sin. But he does not call sinful that which he does not acknowledge to be sinful: which would be a lie of irony.
Reply to Objection 3: A man should not commit one sin in order to avoid another: and so he ought not to lie in any way at all in order to avoid pride. Hence Augustine says (Tract. xliii in Joan.): "Shun not arrogance so as to forsake truth": and Gregory says (Moral. xxvi, 3) that "it is a reckless humility that entangles itself with lies."
Objection 1: It seems that irony is not a less grievous sin than boasting. For each of them is a sin through forsaking truth, which is a kind of equality. But one does not forsake truth by exceeding it any more than by diminishing it. Therefore irony is not a less grievous sin than boasting.
Objection 2: Further, according to the Philosopher (Ethic. iv, 7), irony sometimes is boasting. But boasting is not irony. Therefore irony is not a less grievous sin than boasting.
Objection 3: Further, it is written (Prov. 26:25): "When he shall speak low, trust him not: because there are seven mischiefs in his heart." Now it belongs to irony to speak low. Therefore it contains a manifold wickedness.
On the contrary, The Philosopher says (Ethic. iv, 7): "Those who speak with irony and belittle themselves are more gracious, seemingly, in their manners."
I answer that, As stated above (Q[110], AA[2],4), one lie is more grievous than another, sometimes on account of the matter which it is about---thus a lie about a matter of religious doctrine is most grievous---and sometimes on account of the motive for sinning; thus a mischievous lie is more grievous than an officious or jocose lie. Now irony and boasting lie about the same matter, either by words, or by any other outward signs, namely, about matters affecting the person: so that in this respect they are equal.
But for the most part boasting proceeds from a viler motive, namely, the desire of gain or honor: whereas irony arises from a man's averseness, albeit inordinate, to be disagreeable to others by uplifting himself: and in this respect the Philosopher says (Ethic. iv, 7) that "boasting is a more grievous sin than irony."
Sometimes, however, it happens that a man belittles himself for some other motive, for instance that he may deceive cunningly: and then irony is more grievous.
Reply to Objection 1: This argument applies to irony and boasting, according as a lie is considered to be grievous in itself or on account of its matter: for it has been said that in this way they are equal.
Reply to Objection 2: Excellence is twofold: one is in temporal, the other in spiritual things. Now it happens at times that a person, by outward words or signs, pretends to be lacking in external things, for instance by wearing shabby clothes, or by doing something of the kind, and that he intends by so doing to make a show of some spiritual excellence. Thus our Lord said of certain men (Mat. 6:16) that "they disfigure their faces that they may appear unto men to fast." Wherefore such persons are guilty of both vices, irony and boasting, although in different respects, and for this reason they sin more grievously. Hence the Philosopher says (Ethic. iv, 7) that it is "the practice of boasters both to make overmuch of themselves, and to make very little of themselves": and for the same reason it is related of Augustine that he was unwilling to possess clothes that were either too costly or too shabby, because by both do men seek glory.
Reply to Objection 3: According to the words of Ecclus. 19:23, "There is one that humbleth himself wickedly, and his interior is full of deceit," and it is in this sense that Solomon speaks of the man who, through deceitful humility, "speaks low" wickedly.