If one hears a someone from Israel [an Israelite - a Jew] recite just single blessing, even if they didn't hear the entire blessing from the beginning to the end, and even if they are not bound by that bracha, they are obligated to respond with "amen." But, if the one saying the blessing was an Epikoros [heretic, one irreverent of religious authority], or a Cuthean [Samaritan], or a child, or was one who was changing/deviating from the fixed form of the blessing, one would not say "amen" afterwards.

Rema - One says "amen" if one hears a full bracha said by a non-Jew.

For rain and other good tidings, one recites the special blessing: Blessed…Who is good and Who does good. Even for bad tidings, one recites a special blessing: Blessed…the true Judge. Similarly, when one built a new house or purchased new vessels, he recites: Blessed…Who has given us life, sustained us, and brought us to this time. The mishna articulates a general principle: One recites a blessing for the bad that befalls him just as he does for the good. In other words, one recites the appropriate blessing for the trouble that he is experiencing at present despite the fact that it may conceal some positive element in the future. Similarly, one must recite a blessing for the good that befalls him just as for the bad.

It was taught, "Rabbi Meir used to say, 'A person must make one hundred (meah) blessings each day, as it is stated (Deuteronomy 10:12), "And now Israel, what (mah) does the Lord, your God, ask of you." Rav Ḥiyya, son of Rav Avya, would endeavour to make up this number by the use of spices and delicacies (for which a blessing is required).

It was taught [in a Baraita]: R' Meir used to say: "A man is obligated to recite three blessings every day, and they are the following: ...Who has made me a Jew; ...Who has not made me a woman; ... who has not made me a boor" ...

(1) When a person wakes from his sleep, he says "Elohai neshama." When he hears the voice of a rooster, one blesses "He who gives understanding." When he gets dressed, he blesses "Who clothes the naked." When he passes his hand in front of his eyes, he blesses "Who gives sight to the blind." When he sits, "Who frees the bound." When he stands, "Who straightens the bowed." When he puts his feet on the ground, he blesses "Who stretches the earth over the water." When he puts on his shoes, "Who provides me with all of my needs." When he goes out, he blesses "Who prepares the steps of man." When he puts on a belt, "Who girds Israel with strength." (Gloss: Or if he wears a sash that is sufficient to separate his heart and groin areas [beit Yosef in the name of the Ravad]) When he puts a hat or turban on his head, he blesses "Who crowns Israel with glory." When he washes his hands, he blesses "regarding the washing of hands." When he washes his face, he blesses "who removes the sleep from my eyes etc." and "may it be Your will etc." until "blessed are You Hashem who bestows loving-kindness on His people Israel." One does not answer 'Amen' after "who removes sleep from my eyes" until he has finished with "bestows loving-kindness on His people Israel," because it is all one single blessing.

(1) If one sees a place where miracles have been done for Israel, he says, “Blessed be the One who made miracles for our ancestors in this place.” [If one sees] a place from which idolatry has been uprooted, he should say, “Blessed be the One who removed idolatry from our land.”

(2) [On witnessing] comets, earthquakes, thunder, or windy storms one says, “Blessed be He whose strength and might fill the world.” [On seeing] mountains, hills, seas, rivers or deserts one says, “Blessed be He who made creation.” Rabbi Judah says: one who sees the Great Sea should say, “Blessed be He who made the Great Sea,” if he sees it at intervals. For rain and for good news one says, “Blessed be He that is good and grants good.” For bad news one says, “Blessed be the true judge.”

(3) One who has built a new house or bought new vessels says, “Blessed be He who has kept us alive [and preserved us and brought us to this season.]” One who blesses over the evil as he blesses over the good or over the good as he blesses over evil; one who cries over the past, behold this is a vain prayer. How so? If his wife was pregnant and he says, “May it be his will that my wife bear a male child,” this is a vain prayer. If he is coming home from a journey and he hears a cry of distress in the town and says, “May it be his will that this is not be those of my house,” this is a vain prayer.

(4) One who enters into a large city should say two prayers, one on entering and one on leaving. Ben Azzai says: four two on entering and two on leaving, he gives thanks for the past and cries out for the future.

(5) One must bless [God] for the evil in the same way as one blesses for the good, as it says, “And you shall love the Lord your God with all your heart, with all your soul and with all your might” (Deuteronomy 6:5). “With all your heart,” with your two impulses, the evil impulse as well as the good impulse. “With all your soul” even though he takes your soul [life] away from you. “With all your might” with all your money. Another explanation, “With all your might” whatever treatment he metes out to you.

Whoever sees a place where miracles were done for Israel should say, “Blessed [is the One] who did miracles for our fathers in this place.” For a place that had idol worship uprooted from it, say, “Blessed [is the One] who uprooted idol worship from our land.”

On comets, and on earthquakes, and on lightning and on thunder, and on storms say, “Blessed [is the One] whose strength and might fill the world.” On mountains, and on hills, and on seas, and on rivers, and on deserts say, “Blessed [the One] who makes the works of the beginning.” R’ Yehuda says, “One who sees the great sea says, ‘Blessed [the One] who made the great sea,’ only if he sees it occasionally.” On rain and on good news say, “Blessed is He who is good and does good.” And on bad news say, “Blessed [are You] the true judge.”

When one builds a new house, and acquires new vessels, they say, “Blessed [is the One] that kept us alive [and sustained us and brought us to this time].” Bless upon the bad which contains good, and upon the good which contains bad.

It was taught in a baraita, Rabbi Meir used to say: A Person must bless one hundered blessings every day, as it says (Deuteronomy 10:12): "Now Israel what (mah) does God as of you" - don't read "mah" rather "meah".

(1) It is an affirmative precept of the Torah to say Grace after a meal, as it is said, "And thou shalt eat and be satisfied and shalt bless the Lord, thy God" (Deuteronomy 8:10). The Torah only imposes the obligation on a person when he is satisfied; for it is said, "When thou hast eaten and art satisfied, thou shalt bless etc." According to the ordinances of the sages, however, even if one has eaten only as much food as the size of an olive, he recites Grace after the meal.

(2) It is also an ordinance of the Sages that before partaking of any food, a blessing is first recited and then it is eaten. And however little one intends to eat or drink, the blessing is first recited and then the refreshment is taken. So too, one who wishes to smell a fragrant odor first recites the blessing and then enjoys the fragrance. Whoever partakes of any enjoyment without reciting a blessing commits a trespass. It is also an ordinance of the sages that a blessing is to be recited after eating or drinking, provided that the quantity drunk is at least a quarter of a log (equal to the volume of an egg and a half), and the food eaten is at least as much as an olive in size. A cook who is tasting food does not need to recite a blessing before or after doing so, provided that the quantity tasted is less than a quarter of a log.

(3) And just as blessings are recited when partaking of material enjoyments, so when about to fulfill any precept, a blessing is said, after which the precept is performed. The sages have moreover instituted several blessings of praise and thanksgiving and petition, in order that when not partaking of material enjoyments nor engaged in the fulfillment of religious duties we should constantly have God in mind.

(4) All blessings accordingly fall into three kinds; blessings recited when partaking of material enjoyments, blessings recited when fulfilling religious duties, and blessings of thanksgiving, which have the character of praise, thanksgiving and supplication, and the purpose of which is that we should always have the Creator in mind and revere Him.

(5) The forms of all the blessings were established by Ezra and his Court. It is not proper to vary them, or add to or take aught away from any one of them. Whoever deviates from the form which the Sages have given to the Blessings, is in error. Any blessing in which the name of God and His Sovereignty are not mentioned is not regarded as a blessing, unless it follows immediately another blessing.

(6) All blessings may be recited in any language, provided that the form instituted by the sages is followed. And if the form has been changed, the duty of reciting the blessing is discharged, since the name of God and His sovereignty as well as the subject matter of the blessing have been mentioned, even though in a foreign tongue.

(7) All blessings should be so recited that the reciter hears what he is saying. But if he has not recited the blessings so that he can hear them, he has nevertheless fulfilled his duty, whether he uttered them with his lips or recited them mentally.

(8) There must be no interruption between the recital of any blessing and that for which it is recited. If such an interruption has taken place, the blessing must be repeated. If the interruption was in connection with matters appertaining to the blessing, the blessing need not be recited a second time. For example, a person recites the blessing over bread; and, before he eats it, says "Bring salt", "bring the cooked course", "give food to So and So", "Feed the cattle", he need not recite the blessing a second time. The same is the rule in similar cases.

(9) All blessings may be recited by one ritually unclean, whether the uncleanness is of such a nature that he can free himself of it the same day or not. It is forbidden to a male to recite blessings while in a nude state.

(10) Blessings, even when they have already been recited by a person in fulfillment of his obligation, may be said by him, a second time, on behalf of others who have not said them, so as to free them of their obligation. Blessings recited on partaking of refreshments, when this is not a religious duty, form an exception. A person may only recite the blessings on behalf of others, when he also partakes of the refreshment. But when the refreshment is also a religious duty, as, for instance, eating unleavened bread on the first nights of Passover, eating bread or drinking wine at the inauguration of Sabbath and Festival, a person may recite the blessings for others who eat and drink, without having to join them.

(11) He who hears any blessing from beginning to end, with the intent to fulfill his obligation (to recite that blessing) has fulfilled his obligation, even if he has not responded "Amen". Whoever responds Amen after a blessing has been said is in the same category with the reciter, provided that the latter was under the obligation of saying such a blessing. If the reciter's obligation was only Rabbinical, while the respondent's was Scriptural, the latter does not fulfill his duty unless he responds Amen or listens to the recital of the blessing by one who is under a scriptural obligation.

(12) When several persons had agreed to eat bread or drink wine in company, and one of them recited the blessing, while all the rest responded "Amen", they are permitted to eat and drink. If, however they had not intended to have a meal together but each came (without preconcerted arrangement) even though they should be eating of the same loaf, each of them recites the blessing for himself. This rule refers to bread and wine only. The consumption of other foods and beverages does not require an agreement to form one party. If any one of those present recites the blessing and the rest respond "Amen", they may all eat and drink, even if originally they had had no intention to form one company.

(13) Whoever hears an Israelite recite a blessing has to respond "Amen", even if he has not heard the entire blessing from beginning to end, and even if he himself is not under an obligation to recite that blessing. If however the reciter was an idolater, a free thinker (Epikoros), a Samaritan, a child practising blessings, or an adult who deviated from the fixed form of the blessing, no response of Amen is made.

(14) Whoever responds "Amen", must not utter it with the first or last letter clipped, or unduly hurried or drawn out, but should utter it in the way it is ordinarily pronounced. He should not raise his voice above that of the reciter of the blessing. A person who is under an obligation to recite a blessing and has not heard it recited by another may not join the hearers in responding Amen.

(15) Whoever recites a blessing unnecessarily takes the name of God in vain and is like one who swears in vain. After such a blessing it is forbidden to respond Amen. But children are taught the blessings in their regular form. Although while they are learning, they recite the blessings without due occasion, this is permitted. There must however be no response (of Amen) to such recitals, nor does any one who responds Amen discharge his obligation if he had occasion to recite such blessings.

(16) Whoever responds Amen to the blessings which he himself says acts objectionably; but to add Amen to the last of concluding blessings is laudable; as, for instance, after the phrase, "Who rebuildeth Jerusalem" in the Grace after meals, or after the last of the blessings recited after the Shema in the Evening Service, or at the close of the concluding blessings the reciter responds Amen to his own recital of the blessings.