Berakhot

, because [we assume that] it is with their approval  since he [thereby] makes [the zimmun] obligatory on them. Come and hear: Women by themselves invite one another, and slaves by themselves invite one another, but women, slaves and children together even if they desire to invite one another may not do so. Now  a hundred women are no better then two men,  and yet it says, Women by themselves invite one another and slaves by themselves invite one another? — There is a special reason there, because each has a mind of her own.  If that is so, look at the next clause: Women and slaves together, even though they desire to invite one another may not do so. Why not? Each has a mind! — There is a special reason in that case, because it might lead to immorality. We may conclude that it was Rab who said, 'Even though they [two] desire to invite one another they may not do so', because R. Dimi b. Joseph said in the name of Rab: If three persons ate together and one of them went out, the others call to him and count him for zimmun.  The reason is, is it not, that they call him, but if they did not call him they could not [invite one another]? — There is a special reason there, that the obligation to invite one another devolved upon them from the outset. Rather you may conclude that it is R. Johanan who said that even though they desire to invite one another they may not do so. For Rabbah b. Bar Hanah said in the name of R. Johanan: If two persons eat together, one of them is exempted by the benediction of his fellow; and we were perplexed to know what it was that he tells us; for we have learnt: If he heard without responding [Amen], he has performed his obligation, and R. Zera explained that he tells us that they do not invite one another to say grace.  We may therefore draw this conclusion. Raba b. R. Huna said to R. Huna: But the Rabbis who came from the West  say that if they desire to invite one another they may do so; and must they not have heard this from R. Johanan?  — No; they heard it from Rab before he went down to Babylon. The [above] text [stated]: 'R. Dimi b. Joseph said in the name of Rab: If three persons ate together and one of them went out into the street, they can call to him and count him for zimmun'. Abaye says: This is only when they call to him and he responds.  Mar Zutra said: This applies only to three; but if it is for [the purpose of completing] ten,  they must wait till he comes. R. Ashi demurred to this. We should rather [he said], suppose the contrary; for nine look like ten, but two do not look like three. The law, however, is as laid down by Mar Zutra. What is the reason? — Since they [ten] have to mention God's name,  it is not proper that there should be less than ten. Abaye said: We have a tradition that if two persons have eaten together, it is their duty to separate.  It has been taught similarly: If two persons have eaten together, it is their duty to separate. When is this case? When they are both educated men. But if one is educated and the other illiterate, the educated one says the benedictions and this exempts the illiterate one. Raba said: The following statement was made by me independently and a similar statement has been made in the name of R. Zera: If three persons have been eating together, one breaks off to oblige two,  but two do not break off to oblige one. But do they not? Did not R. Papa break off for Abba Mar his son, he and another with him? — R. Papa was different because he went out of his way  to do so.  Judah b. Meremar and Mar son of R. Ashi and R. Aha from Difti took a meal with one another. No one of them was superior to the other  that he should have the privilege of saying grace.  They said: Where the Mishnah learnt  that IF THREE PERSONS HAVE EATEN TOGETHER IT IS THEIR DUTY TO INVITE [ONE ANOTHER TO SAY GRACE], this is only where one of them is superior [to the others], but where they are all on a level, perhaps it is better that the blessings should be separate. They thus said [the grace] each one for himself. Thereupon they came before Meremar and he said to them: You have performed the obligation of grace, but you have not performed the obligation of zimmun. Should you say, Let us start again with zimmun, zimmun cannot be said out of its place. If one came and found three persons saying grace,  what does he say after them? — R. Zebid says: Blessed and to be blessed [be His Name]. R. Papa said: He answers, Amen. They are not really at variance; the one speaks of the case where he found them saying 'Let us say grace', and the other where he found them saying 'Blessed'. If he found them saying 'Let us say grace', he answers 'Blessed and to be blessed'; if he found them saying 'Blessed', he answers 'Amen'. One [Baraitha] taught: One who answers 'Amen' after his own blessings is to be commended, while another taught that this is reprehensible! — There is no contradiction: the one speaks of the benediction 'who buildest Jerusalem',  the other of the other benedictions. Abaye used to give the response  in a loud voice so that the workmen should hear and rise,  since the benediction 'Who is good and does good'  is not prescribed by the Torah.  R. Ashi gave the response in a low voice, so that they should not come to think lightly of the benediction 'Who is good and does good'.