Kitzur Shulchan Aruch, Rabbi Shlomo Ganzfried
Siman 15: The Laws of Kaddish, Barechu, Requirements of Minyan, and the Laws of the Chazzan
After [completing] Yishtabach the chazzan says half-Kaddish. Kaddish, Barechu and Kedushah cannot be said and the Torah cannot be read unless there are ten adult men present. If ten men were not present when Yishtabach was said but, the minyan was completed afterwards, then, the chazzan may not say Kaddish, because Kaddish is said only following something that was said by ten men. They should, therefore, wait to say Yishtabach until ten [men] arrive. They may wait until almost a half-hour. They should not wait longer, but, rather, they should say Yishtabach and then wait. When ten [men] arrive they should first say a few verses, and afterwards the chazzan says half-Kaddish.
An adult, is one whose thirteenth year has passed and he has entered his fourteenth year (we may rely on the assumption that he has probably grown two pubic hairs.) For example: If he was born on Rosh Chodesh Nissan, he does not attain adulthood until Rosh Chodesh Nissan; that is, at the beginning of the night of Rosh Chodesh Nissan; thirteen years after birth, he becomes an adult. If he is born in the month of Adar during a regular year and when reaching adulthood it is a leap year, he does not attain adulthood until the second Adar. But, if he is born on the first Adar of a leap year, he also attains adulthood during the first Adar. If he is born during a leap year and he reaches adulthood during a regular year, regardless of whether he was born during the first Adar or during the second Adar — he attains adulthood on his birthday during the Adar of the present [year]. Thus, at times, the result is that a boy born before his friend, may attain adulthood later than his friend who was born after him. For example: they were both born during a leap year; one on the twentieth of Adar I, and the second on the tenth of Adar II, and the year they attain adulthood is a regular year.
Care should be taken not to take a head-count of people to verify whether there is a minyan, because it is forbidden to take a head-count of Jews even for the purpose of a mitzvah, for it is written: "And Saul gathered the nation and counted them by means of lambs." It is customary to count them by reciting the verse: "Hoshiah es amecha etc..." which contains ten words.
It is necessary that all ten [men] be in one place and the chazzan with them. If some are in one room and some in another room, they are not considered combined, though the door between them is open. Even if the majority are in the synagogue and the minority are in the vestibule in front of the synagogue, they are not drawn to the majority to be combined with them. Even those standing on the threshhold, within the opening on its outer flank, that is — when the door is closed — that place is on the outside, though the door may now be open, nevertheless, it is considered outside. All this applies to combining ten [for a minyan], but, if there were ten and they are saying Kaddish, Barechu or Kedushah, then, whoever hears them may respond with them, even if many houses separate them [from the main minyan], because even an "iron curtain" cannot separate Israel from their Father in Heaven, provided that there was no excrement or idolatry present there."
You should take great care to listen to the Kaddish and respond with concentration. Certainly at "Amein, yehei shemei rabba..." you should concentrate well, for, who ever responds, "Amein, yehei shemei rabba...", with all his strength and concentration his decree of seventy years is nullified. The response should he loud, because with this sound you can shatter all the indictments and nullify all evil decrees. Nevertheless, you should not overshout so that people will not ridicule you thereby, causing them to sin. "Amein, yehei shemei rabba..." is said along with the word: "yisbarach". Afterwards you should listen to the chazzan and respond: Amein.
Some authorities maintain that you are not required to stand during Kaddish. But, if you are already standing when Kaddish is to be said for instance, after Hallel, you should remain standing until after: "Amein, yehei shemei rabba..." Others hold the opinion that you should always stand during Kaddish as well as during other prayers of Kedushah. This can be derived by means of a "kal v'chomer" from the case of Eglon, king of Moab, for it is written: "Ehud came to him etc. and Ehud said: have brought you a word of God. 'And he (Eglon) stood up from his throne." If Eglon King of Moab, who was an idol worshipper, rose [to hear] the word of God, how much more so, [should] we, who are His people. Therefore, it is preferable to be stringent.
If there are not nine [men] listening to the chazzan he should not say Kaddish at all because a sacred prayer should not be said with less than ten; that is one reciting and nine listening. Nevertheless, if one of the ten is in the middle of his Shemoneh Esrei although he cannot respond with them he may be counted [in the ten]. The same applies to two, three or four, [who are in mid Shemoneh Esrei] as long as there is a majority responding, then the response of the minority is not a necessity. However, if one of them is asleep, he should be wakened because one who is sleeping cannot be counted in the ten.
After the chazzan says half-Kaddish, he says aloud: "Barechu es Hashem hamevorach", and the congregation responds: "Baruch Hashem hamevorach le'olam va'ed", and the chazzan, as well, repeats: "Baruch Hashem hamevorach le'olam va'ed", so that he does not exclude himself from the congregation, by telling them to bless [God] and he himself does not do so. There are some whose custom it is to respond Amein to the chazzan. But the chazzan should not respond after the congregation's blessing. If the chazzan prolongs the melody while saying Barechu, the congregation says Yisbarach etc. [However,] it should be said only while he (the chazzan) sings, but while he says the words, they should say nothing, but rather listen to what he is saying. Even if you did not hear the chazzan saying Barechu but only heard the congregation respond Baruch etc., you may respond along with them.
The Kedusha of Yotzeir should preferably be said with the congregation. But, if this is not possible you may also say it individually.
If there is only an exact minvan, in the synagogue it is prohibited for any of them to leave. Of one who leaves it is said: "Those who abandon God will be consumed." But, if ten will remain, the rest may leave if they have already heard Barechu, Kedushah and the Kaddishim after Aleinu. In the event that less than ten were left, they may conclude the prayers, even with less than ten (provided that they are a majority of a minyan). If the chazzan had started to repeat the Shemoneh Esrei he may complete the entire repetition of the Shemoneh Esrei and the congregation may say Kedushah, and he (the chazzan) also says: "Elokeinu veilokei avoseinu barecheinu baberachah etc." However, the kohanim do not bless the congregation. Also, the Kaddish that follows the Shemoneh Esrei is not said because these are different subjects. If they began the Torah reading with ten men and some [congregants] leave, the reading may be completed, but no additional [aliyahs] are permitted, and no one is called for maftir, but, rather, the last of the allotted olim reads the Haftarah without the berachos.
The chazzan must be a worthy person for it is said: [God says of His nation]: "She raises her voice at Me, I therefore, have contempt for her," and our Rabbis of blessed memory, said, that this refers to an unworthy chazzan who, [nevertheless,] goes down to the Amud. Who is considered worthy? One who is free of sin and who is respectful, that is, his reputation is untarnished, and was unblemished even during his youth; and one who is humble and acceptable to the congregation so that they agree that he lead the prayers. He should have a pleasant and a sweet voice, which draws [appeals to] the heart, and he should be one who regularly reads the Scriptures, so that the verses in prayer are fluent in his mouth. If a person cannot be found with all these attributes, [then] they (the congregation) should choose one among them who excels in wisdom and good deeds.
No person may pray [at the Amud] against the will of the congregation. If one does pray without permission, through intimidation and arrogance, [the congregation] should not respond "Amein" after his berachos, as it is said: "And the brazen utters a blessing, he has mocked Hashem."
No one should be appointed a permanent chazzan whose beard is not fully grown. But, on occasion, any male who has passed his thirteenth year may "go down" to the Amud.