Rabbi Moshe Menachem Liberman, a member of the Chicago Community Kollel discusses some of the halachos regarding the modification of the truth for certain purposes.
http://www.cckollel.org/html/parsha/bereishis/vayichi5764.html
“And they sent a message to Yoseph saying: Your father commanded before he died, saying: So you shall say to Yoseph: Please forgive now the transgression of your brethren, and their sin, for they did to you evil . . .” Vayechi 50:16-17. Rashi points out that the brothers modified the words of Yaakov Avinu in this matter in the interest of peace because Yaakov Avinu had not actually commanded thus.1 The Gemara learns from these pesukim that there is a license to alter the truth in the interest of peace.2 This freedom to alter the truth is actually mandatory and not merely an authorization to alter the truth.3 Before we look at this obligation to alter the truth in the interest of peace, it behooves us to examine the general restriction against altering it.
The Torah states in Parshas Mishpatim, “From a false matter you shall distance yourself.”4 Thus, halachic authorities hold that there is a biblical obligation to refrain from lying.5 Furthermore, Hashem exhorts us to speak the truth, as the Navi in Zechariah states, “Let one man speak with another in truth.”6
The threshold for establishing what constitutes a falsehood, though, is very low. A mere omission is considered an alteration of the truth.7 The Chofetz Chaim deduces this from our Gemora, which states:
Peace is important because even Hakodosh Boruch Hu altered the truth in the interest of peace. Initially the Torah writes [that Sarah Imeinu, after hearing that she will give birth to a son to Avraham Avinu, said], “[After I am old shall my skin become smooth] and my husband is old?”8 And afterwards it writes [Hashem (only) told Avraham Avinu that Sarah Imeinu had said], “and I am old?”9 The only difference between what Sarah Imeinu said and what Hashem told Avraham Avinu that she said, was that Hashem omitted the comment that she had made concerning Avraham Avinu.10 This omission, the Gemara said, was permitted only because it was done in the interest of peace.11 Thus, even a mere omission of part of an otherwise true statement is considered a falsehood to which we are commanded to keep our distance.12
Although merely omitting is considered a falsehood, when altering the truth in the interest of peace, it is preferred to an outright lie.13 Of course, if merely omitting would be insufficient then he should outright lie.14 This obligation to lie in the interest of peace, however, does not sanction swearing falsely.15 Additionally, one may not lie concerning things which have not yet happened.16
There are other times when it is also appropriate to lie. If a person is asked whether he is knowledgeable in a certain Mesechta, he may lie and answer that he is not when in fact he is.17 However, if he is asked in order to provide an answer to a halachic query or to teach, then he must answer truthfully, consistent with his expertise in the Mesechta.18 If a person is asked in the presence of disreputable people concerning the graciousness of his host, he may lie and answer that his host was not gracious.19
The contemporary halachic authorities also permit altering the truth in the following circumstances:
• People may answer, “I don't know” when asked about a matter that is supposed to remain secret.20
• Wealthy individuals may lie about their wealth if they fear “the evil eye” (ayin hara) or if they do not want to arouse jealousy.21
• If one fears that a package will be mishandled, it is permitted to write “glass” on it, even though it does not contain any glass.22
_______________________________________________________________________________________________________________________________
1 Rashi al Hatorah, Vayechi 50:16 (beginning with the words “Your father commanded”)
2 Yevamos 65b
3 Derishah al Choshen Mishpat 262:21
4 23:7.
5 Rabbi Shmuel Hominer, Eved HaMelech, Parshas Mishpatim 23:7:1 (citing SMa”G at Esay 107 and SMa”K 226) (4th ed. 1998); but see Rabbi Menachem Trivash, Orach Maysharim 9:1:1 (noting that this verse is only a restriction on judges and witnesses in the judicial context) (3d ed. 1968).
6 Mesilas Yesharim Chapter 11 (quoting Zechariah 8:16 and other sources).
7 Chofetz Chaim Hilchos Rechilus 1:8:14.
8 Vayera 18:12.
9 Id. at 18:13.
10 Chofetz Chaim Hilchos Rechilus 1:8:14.
11 Id.
12 Id.
13 Chofetz Chaim Hilchos Rechilus 1:8.
14 Id.
15 Id.; but see Chofetz Chaim Hilchos Rechilus 1:8:15 (noting that if there is a foreseeable loss to the other person it is questionable whether swearing falsely may be permitted).
16 Magen Avraham 156:2 (citing Sefer Chasidim 426); but see Mishnah Berurah 156:4 (commenting on Magen Avraham 156:2 that it is questionable); see Rabbi Shmuel Hominer, Eved HaMelech, Parshas Mishpatim 23:7:2 (explaining that the Mishnah Berurah does not understand why there should be a limitation as to when one may alter the truth in the interest of peace).
17 Shulchan Aruch Choshen Mishpat 262:21.
18 Be'er HaGolah al Choshen Mishpat 262:9.
19 Shulchan Aruch Choshen Mishpat 262:21.
20 Rabbi Doniel Yehuda Neustadt, The Weekly Halachic Discussion, 47 (citing Titen Emes l'Yaakov at 76 (quoting Harav S.Z. Auerbach and Harav S.Y. Elyashiv)) (2d rev. ed. 2002).
21 Id. (citing Titen Emes l'Yaakov at 78 (quoting Harav S.Y. Elyashiv)).
22 Id. at 48 (citing Titen Emes l'Yaakov at 66 (quoting Harav S.Y. Elyashiv, Harav Y.Y. Fisher, and Harav C. Kanievsky)).