A Samaritan who blesses with the divine name--one does not respond amen until one hears the entire blessing.
Although there are variations among the textual witnesses to these passages, the basic idea of all the versions is that a Jew should respond amen whenever someone blesses God, as long as this person is not reciting an improper blessing.
To be sure, the rabbis would not respond amen if a gentile were to drink a libation to Mars.
13), Maimonides rules that one never responds amen to blessings said in vain, including those said by gentiles, Apikorsim and Samaritans.
Elijah, the Gaon of Vilna, could explain the Rambam's strange ruling only as a scribal error: "These words [of R Yosef Karo] indicate that one should not respond amen to a Samaritan, even if one heard the entire blessing.
His brief explanation for why one should respond amen to the complete blessing of a Samaritan or non-Jew is resonant with religious meaning, and it bears examination: "Since one hears that this [Samaritan] has blessed God upon this item-even though he does not even know what God is, for he thinks that his idol is the Creator
Rather, through the religious act of saying amen, the Tosafot Yom Toy embraced a wide range of human beings who direct their prayer to God.
My concern that Orthodox Jews respond amen to my blessings is not to satisfy a personal need for their approval.
This inverts the social valence the Sages assigned to amen, unfortunately, altogether missing the unifying power of this communal response.
Yehuda Sirilion at Berakhot 53b from the late twelfth- or early thirteenth-century record the numerological explanation that the value of amen, 91, equals that of YHVH and Adonay (26+65).
To these, we must answer amen when we hear the entire blessing from their mouths.
If it is known that his desecration of Sabbath was only because he could not control his lust, such as if he regularly prays and lays tefillin, then his blessing is a blessing and one responds amen, for his intention is toward heaven.
One may conclude that the conditions for saying amen apply when one hears either statutory prayers or blessings of thanksgiving.
Authorities differ about the minimum amount of a blessing one must hear before responding amen.
Practically, then, non-Jews are to be treated the same was as proper Jews: one always responds amen no matter what one has heard of the blessing.