Objection 1. It seems that lies are not sufficiently divided into "officious," "jocose" and "mischievous" lies. For a division should be made according to that which pertains to a thing by reason of its nature, as the Philosopher states (Metaph. vii, text. 43; De Part. Animal i, 3). But seemingly the intention of the effect resulting from a moral act is something beside and accidental to the species of that act, so that an indefinite number of effects can result from one act. Now this division is made according to the intention of the effect: for a "jocose" lie is told in order to make fun, an "officious" lie for some useful purpose, and a "mischievous" lie in order to injure someone. Therefore lies are unfittingly divided in this way.
Objection 2. Further, Augustine (Contra Mendac. xiv) gives eight kinds of lies. The first is "in religious doctrine"; the second is "a lie that profits no one and injures someone"; the third "profits one party so as to injure another"; the fourth is "told out of mere lust of lying and deceiving"; the fifth is "told out of the desire to please"; the sixth "injures no one, and profits someone in saving his money"; the seventh "injures no one and profits someone in saving him from death"; the eighth "injures no one, and profits someone in saving him from defilement of the body." Therefore it seems that the first division of lies is insufficient.
Objection 3. Further, the Philosopher (Ethic. iv, 7) divides lying into "boasting," which exceeds the truth in speech, and "irony," which falls short of the truth by saying something less: and these two are not contained under any one of the kinds mentioned above. Therefore it seems that the aforesaid division of lies is inadequate.
On the contrary, A gloss on Psalm 5:7, "Thou wilt destroy all that speak a lie," says "that there are three kinds of lies; for some are told for the wellbeing and convenience of someone; and there is another kind of lie that is told in fun; but the third kind of lie is told out of malice." The first of these is called an officious lie, the second a jocose lie, the third a mischievous lie. Therefore lies are divided into these three kinds.
I answer that, Lies may be divided in three ways. First, with respect to their nature as lies: and this is the proper and essential division of lying. On this way, according to the Philosopher (Ethic. iv, 7), lies are of two kinds, namely, the lie which goes beyond the truth, and this belongs to "boasting," and the lie which stops short of the truth, and this belongs to "irony." This division is an essential division of lying itself, because lying as such is opposed to truth, as stated in the preceding Article: and truth is a kind of equality, to which more and less are in essential opposition.
Secondly, lies may be divided with respect to their nature as sins, and with regard to those things that aggravate or diminish the sin of lying, on the part of the end intended. Now the sin of lying is aggravated, if by lying a person intends to injure another, and this is called a "mischievous" lie, while the sin of lying is diminished if it be directed to some good--either of pleasure and then it is a "jocose" lie, or of usefulness, and then we have the "officious" lie, whereby it is intended to help another person, or to save him from being injured. On this way lies are divided into the three kinds aforesaid.
Thirdly, lies are divided in a more general way, with respect to their relation to some end, whether or not this increase or diminish their gravity: and in this way the division comprises eight kinds, as stated in the Second Objection. Here the first three kinds are contained under "mischievous" lies, which are either against God, and then we have the lie "in religious doctrine," or against man, and this either with the sole intention of injuring him, and then it is the second kind of lie, which "profits no one, and injures someone"; or with the intention of injuring one and at the same time profiting another, and this is the third kind of lie, "which profits one, and injures another." Of these the first is the most grievous, because sins against God are always more grievous, as stated above (I-II, 73, 3): and the second is more grievous than the third, since the latter's gravity is diminished by the intention of profiting another.
After these three, which aggravate the sin of lying, we have a fourth, which has its own measure of gravity without addition or diminution; and this is the lie which is told "out of mere lust of lying and deceiving." This proceeds from a habit, wherefore the Philosopher says (Ethic. iv, 7) that "the liar, when he lies from habit, delights in lying."
The four kinds that follow lessen the gravity of the sin of lying. For the fifth kind is the jocose lie, which is told "with a desire to please": and the remaining three are comprised under the officious lie, wherein something useful to another person is intended. This usefulness regards either external things, and then we have the sixth kind of lie, which "profits someone in saving his money"; or his body, and this is the seventh kind, which "saves a man from death"; or the morality of his virtue, and this is the eighth kind, which "saves him from unlawful defilement of his body."
Now it is evident that the greater the good intended, the more is the sin of lying diminished in gravity. Wherefore a careful consideration of the matter will show that these various kinds of lies are enumerated in their order of gravity: since the useful good is better than the pleasurable good, and life of the body than money, and virtue than the life of the body.
This suffices for the Replies to the Objections.
Source: Summa Theologica (New Advent)