The foundational caution comes from Mishlei 27:2, which teaches that a person should be praised by another's mouth and not his own, and this concern is sharpened by Bava Batra 164b-165a, where Rabbi Yehuda HaNasi rebukes even complimentary speech as a form of malicious talk, citing the principle that praise of another leads to his detriment. The Rambam codifies this directly in Mishneh Torah, Human Dispositions 7:4, ruling that one who recounts another's praise before his enemies has committed a form of lashon hara, since this invites the enemies to speak his disgrace, and he grounds this in the verse about blessing one's fellow loudly in the morning being reckoned a curse.
A middle path distinguishes partial praise spoken in a person's presence from full praise reserved for when he is absent, as taught in Eruvin 18b:13, which draws this distinction from the differing ways Lot and Noach are described as righteous. Netivot Olam, Netiv Halashon 7:2 qualifies this further, explaining that the leniency for praise in one's presence applies only to someone already renowned for great fear of Heaven, while for an ordinary person even partial praise in his presence is forbidden lest it provoke others to speak against him. Chiddushei Aggadot, Arachin 16 likewise holds that partial praise may be spoken in presence and complete praise in absence, yet cautions that one should never praise another's good qualities since such praise can lead to his detriment, and Halakhot Ketanot, Part I 261 similarly discusses the scope of this partial-praise principle.
Despite these cautions, the Rambam in Mishneh Torah, Human Dispositions 5:7 instructs a person to speak only of another's praise and never his disgrace, voicing praise when it will be effective and otherwise remaining silent, without distorting his words except for the sake of peace. He roots this obligation in love of neighbor in Mishneh Torah, Human Dispositions 6:3, ruling that one must recount another's praise just as he would want his own money and honor protected, since love of one's fellow as oneself demands it.
Scripture itself models praise being spoken of people, as when a woman is praised by her husband and children for her deeds and her fear of God in Mishlei 31:28-31, and when Yaakov addresses a fitting word to each of his sons in Bereishit 49:28. Yet Mishlei 25:27 warns against excessive searching after honor, and Chiddushei Aggadot, Bava Batra 147 resolves the apparent tension by explaining that praise is not forbidden as lashon hara when it does not include disparagement of the same matter, which is why Rabban Yochanan ben Zakkai could enumerate his students' praises.
Even Sheleimah 1:13 carves out an exception for someone already renowned for good character, holding that such a person should actually be praised, since the danger of praise leading to disgrace does not apply when everyone already praises him and would not believe a slanderous word against him. Jerusalem Talmud Maaser Sheni 2:1 offers a related principle, that praise is proportioned to how recognized the praised quality already is, while unrecognized praise is attributed instead to the second party.
Other sources emphasize the social and spiritual dimensions surrounding praise: Pirkei Avot 2:8 records Rabban Yochanan ben Zakkai enumerating the specific virtues of each of his students, Pesachim 113b teaches that one must show honor to anyone known to be greater in even one respect, and Berakhot 58b shows Sages extending blessings upon encountering one another as a form of honoring praise. Pirkei Avot 4:1 adds that true honor comes from honoring others, and Tomer Devorah, Chapter 1, Tanya, Part I; Likkutei Amarim 30, and Tanya, Part I; Likkutei Amarim 32 all counsel seeing merit in others and drawing them close with love, even those distant from Torah observance.
Rav Eliezer Melamed (Peninei Halakhah, Likkutim II 1:17) sharpens the limitation in a different direction, ruling that it is forbidden to flatter the wicked, since praise of a sinner strengthens him and encourages him to continue in his ways, making the praiser a partner in reinforcing evil in the world.
Shulchan Arukh, Yoreh De'ah 151:14 rules that it is forbidden to praise the beauty of a gentile, and all the more so to praise his deeds or favor his words, unless the praise is intended to thank God for having created such a beautiful creature, in which case it is permitted.
Duties of the Heart, Sixth Treatise on Submission 7:5 cautions that a person who is praised for a good deed should belittle the praise in his own eyes, recognizing how small his good deed is compared to what he truly owes, teaching humility as the proper internal response to receiving praise.
Ran on Pesachim 4a discusses the structure of blessings of praise as distinct from blessings over mitzvot, bearing on the broader category of praise-language even outside the interpersonal context.
Responsa Rav Pealim, Volume IV, Orach Chayim 39 addresses a related but distinct practice, the custom of only eulogizing Torah scholars in the synagogue, reflecting how praise of the deceased is likewise bounded by communal norms rather than freely given to all.
Among the Acharonim who extend this analysis to specific cases, Rav Menashe Klein (Mishneh Halachos 7:243) holds that praising a woman's beauty before others is forbidden, since it may cause others to desire her, while praising her good deeds is permitted and even a mitzvah, drawing on the phrase that her works praise her in the gates. Rav Menashe Klein (Mishneh Halachos 7:116) separately distinguishes forbidden praise of an idolater from permitted praise directed at God for having created beauty, wisdom, or expertise, while allowing factual professional recommendations for a Jew's benefit.
Rav Samson Raphael Hirsch frames the entire topic in terms of the destructive power of speech, teaching that the tongue damages more than the arm and works against happiness and morality, a warning that colors the whole question of praising others.
Tzitz Eliezer (Tzitz Eliezer 15:47) permits praising a person's actions or admiring something they said when the praise simultaneously expresses praise and gratitude to God, treating such God-directed praise as a legitimate exception to the general caution against praising people. Mishneh Halachos (Mishneh Halachos 11:262) likewise permits honoring another with praise, distinguishing this from prohibited speech about business matters and clarifying that it is unrelated to the principle that forbids certain speech while permitting mere thought. B'tzel HaChochma (B'tzel HaChochma 1:46) takes a stricter position, holding that language of honor and favor toward a person remains prohibited even when accompanied by praise of God, though he notes that the Shulchan Aruch appears to permit the specific formula of praising a beautiful person by blessing the One who created such beautiful creatures.
