Gemara

A tied Get was brought in front of Rebbi. He was displeased. His son Shimon said 'I did not write it. Yehudah the scribe wrote it.'

Rebbi: Do not speak Lashon ha'Ra!

Rebbi once praised a Sefer Tehilim. His son Shimon said 'I did not write it. Yehudah the scribe wrote it.'

Rebbi: Do not speak Lashon ha'Ra!

Question: Granted, it was Lashon ha'Ra to say that Yehudah wrote the tied Get. Why was it Lashon ha'Ra to say that he wrote the Sefer Tehilim?

Answer (Rav Dimi, brother of Rav Safra): One should not speak favorably of another, lest this lead to mention of his flaws.

(Rav Amram): Everyone transgressed Lashon ha'Ra every day.

Objection: People do not speak Lashon ha'Ra every day!

Correction: Rather, they transgress Avak Lashon ha'Ra.

Erchin 16a (Rav Dimi): "Mevarech Re'ehu b'Kol Gadol ba'Boker Haskem Kelalah Techashev Lo" refers to one who publicly blesses his host who toiled so much for him. People hear this, and take his money.

Rav Dimi fell ill. He told Rav Safra 'I fulfilled every mid'Rabanan law.'

Rav Safra: Did you fulfill not speaking highly of Ploni, lest this lead to mention of his flaws?

Megilah 25b (Rav Ashi): One may praise a person about whom good reports go out. He will be blessed for doing so.

Yerushalmi Pe'ah (4b): How severe is Avak Lashon ha'Ra! Verses falsified matters to make Shalom between Avraham and Sarah, to cover up her amazement that Avraham, who is old, will have a son. Verses falsified matters to make Shalom between Yosef and his brothers. They told him 'your father commanded to forgive us', and we do not find that Yakov did so.

Rishonim

Rif (Shabbos 14a): "Mevarech Re'ehu b'Kol Gadol..." refers to one who publicly blesses his host... People hear this, and lodge with him. One should never praise someone too much, lest he come to mention his flaws.

Ran (DH v'Sham'ei): The host will be inundated with guests until his money is consumed. If one is praised, listeners will point out flaws.

Rashi (Erchin 16a DH v'Sham'in): Powerful people hear of the host's wealth, and take it by force. If one is praised, the speaker or a listener will point out a flaw in him.

Rambam (Hilchos De'os 7:4): Some things are forbidden due to Avak Lashon ha'Ra. 'Who would have said about Ploni that he would be like he is now', or 'be quiet about Ploni. I don't want to say what happened (with him).' Similarly, if one speaks highly about Ploni in front of Son'av (people who hate Ploni), this is Avak Lashon ha'Ra, for it causes them to speak to his detriment. About such matters it says "Mevarech Re'ehu b'Kol Gadol..."

Kesef Mishneh: The Rambam explains that speaking highly about Ploni is forbidden in front of people who hate him, for it causes them to say 'this is not true. Rather, he has this (bad) trait.' The Rambam implies that one may speak well about someone in front of people who love him.

Hagahos Maimoniyos (5): Avos 2:8 proves that one may speak well about someone in front of people who love him. R. Yochanan ben Zakai used to tell the praises of his Talmidim. However, the Rashbam (164b DH Ba) explains that one should not praise someone too much, for surely he will come to mention his flaws.

Note: Also Semag brought a proof from R. Yochanan ben Zakai. This is no proof according to the Chafetz Chayim (9:2 below, who permits praising one established to be a Tzadik without any flaws).

Iyun Yakov (Erchin 16 Amos DH Tani): The Rambam explains that one should not praise a host lest others mention his flaws.

Emes l'Yakov (Bava Basra 164b), Minchas Chinuch (236:1) and Pri Chodosh (Mayim Chayim, in Likutim in Frankel Rambam): Bava Basra 164b connotes that the Isur is not only in front of Son'av. It is difficult to say that Rebbi hated Yehudah due to the previous incident (of the tied Get).

Perush ha'Mishnayos (Avos 1:17): A Chacham once praised a scribe in front of many people. The Rav rebuked him for Lashon ha'Ra, for amidst the many people some hate the scribe, and hearing his praise will prompt them to mention his faults. This is the ultimate distancing from Lashon ha'Ra.

Note: The Chida (Bris Olam, on Sefer Chasidim 64) says that this answers for the Rambam. Perhaps those who challenged the Rambam (above) rejected this, for Rebbi thought that Shimon wrote it, and he praised it in front of many)! Perhaps Shimon was established to be a flawless Tzadik (see below). However, the Rambam does not bring this Heter!

Yad Eisan (in Likutim in Frankel Rambam): The Rambam explains that the Isur is only in front of Son'av, for Eruvin 18b permits to tell someone's full praise in his absence.

Sha'arei Teshuvah (of R. Yonah, 3:226): Avak Lashon ha'Ra is causing others to speak Lashon ha'Ra.

Be'er Mayim Chayim (Chafetz Chayim Kelal 9)):4): Why do the Rambam and R. Yonah ignore the Lav of Lifnei Iver? It is difficult to say that they mean 'in addition to the Isur of Lifnei Iver.' Perhaps they teach about when the listeners would have spoken Lashon ha'Ra by themselves

Sha'arei Teshuvah (ibid.): It is praiseworthy to praise people. An Evil (scoffer) is one who never praises people. However, one should praise Ploni only when speaking to an individual, but not to a Rabim, unless he knows that no one there hates or envies Ploni. One may praise a person established to be a Tzadik without any flaws, even in front of Son'av and those who envy him, for they cannot speak bad about him. They know that if they speak bad about him, everyone will say 'you lie!'

Sha'arei Teshuvah (227,228): One may speak bad about sinners to prevent others from doing so, but he must beware lest he be suspected of Lashon ha'Ra. If he brings himself to suspicion, this is Avak Lashon ha'Ra. People might suspect that he did not first tell the sinner, or that he lies. Therefore, if he first openly rebuked him, or he is established to speak only the truth and not to fear people, it is permitted.

Sefer Chasidim (64): One should not praise an Ashir (wealthy person) in front of an Ashir, nor a scribe in front of a scribe, etc. One may praise one with Yir'as Shamayim in front of Yir'ei Shamayim, for this will not cause envy. Rather, he will want to act similarly.

Pnei Moshe (Pe'ah 4b DH Kamah): What Sarah said about Avraham was only Avak Lashon ha'Ra. It is no detriment to say that he is old! Yosef's brothers lied to him, for they feared lest he accepted Avak Lashon ha'Ra about them, which would cause him to remember what they did to him.

Poskim

Magen Avraham (156:2): Examples of Avak Lashon ha'Ra are 'who would have said about Ploni that he would be like he is now', or 'be quiet. I don't want to say what happened.' Also, speaking highly about Ploni in front of people who hate Ploni, is Avak Lashon ha'Ra, for it causes them to speak to his detriment. Rashi explains that it is speaking too highly about him, for surely he will come to mention his detriment. This is difficult, for Rebbi praised a Sefer Tehilim, his son Shimon said 'I did not write it. Yehudah the scribe wrote it', and Rebbi rebuked him for speaking Lashon ha'Ra!

Chafetz Chayim (9:1): It is Avak Lashon ha'Ra to speak highly about Ploni in front of people who hate Ploni, for it causes them to speak to his detriment. The same applies to speaking too highly about him, for then he is apt to speak to his detriment in the end, e.g. 'except for this bad trait that he has.' Or, the listeners will say 'why do you praise him so much? He has this bad trait!'

Be'er Mayim Chayim (4): Therefore, if one knows that Ploni dislikes the Rav or Beis Din of the city, and he has a Din Torah, one may not ask him afterwards what happened, for he is prone to say bad things about the Beis Din. In our many sins, many people resent the Beis Din due to one ruling against them, therefore even if one does not know that Ploni dislikes the Beis Din, one should not ask him what the outcome was. It is permitted only if the law is relevant for the one who asks.

Chafetz Chayim (9:2): It is always forbidden to praise Ploni in public, for normally some of them hate or envy him, and they will mention his faults. One may praise a person established to be a flawless Tzadik, even in front of Son'av.

Be'er Mayim Chayim (7): One should not sit among people praising even Gedolei ha'Dor, for in the end they will come to Lashon ha'Ra. Lashon ha'Ra about Gedolim is far more severe than about a Stam Yisrael.

Note: It is a Chidush that Gedolei Yisrael are not established to be Tzadikim without any flaws!

Chafetz Chayim (9:3): One may not praise Ploni in a way that will cause a loss, e.g. to publicize Ploni's generous hospitality. Through this, empty people will gather to Ploni and consume his money. One should not publicize that Ploni lent to him, for this often causes evil people to gather to him, and he cannot evade them. One must not bring himself to be suspected of Lashon ha'Ra.