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Davening with a minyan
A person should make a great effort to daven in a minyan because of the tremendous holiness of Davening in a minyan and when one prays in a minyan one's Tefillot are accepted before Hashem. 
For what parts of Davening is a minyan necessary?
- A congregation may not say Kaddish, Kedusha, or Barchu with less than a minyan, meaning a quorum of ten adult men.
- If there is a minyan of ten adult males, but four of them already davened, the congregation may still say kaddish, borchu, and kedusha. 
- According to the halacha, it is permissible to start Chazarat HaShatz even if 4 people in the minyan are still davening the silent Shemona Esreh. However, it's better to wait until there is ten who are able to answer before starting Chazarat HaShatz.
If some of the minyan left in middle
- If there’s only 10 men in the minyan, none of them may leave in middle. However, if there’s more than 10 men, those who are in excess of 10 may leave if they already heard Barchu, Kedusha, and all the Kaddishim. 
- After the fact, if there’s not ten men left, they are allowed to finish what they’re involved with as long as there’s at least 6 men left. 
- If the Shaliach Tzibbur began Chazarat HaShatz he may finish Chazara including Kedusha, but there’s no Nesiyat Kapayim and he may not say Kaddish after the Chazara. 
- If the minyan began Kriyat HaTorah and then part of the minyan left (four or less), they may finish the Kriyah but may not do Hosafot and the maftir is said without Brachot. 
Missing a Minyan for business
- It’s permissible to miss a minyan in order to prevent a loss of money, however, it’s forbidden if it’s just a loss of a potential profit. 
Missing a Minyan for vacation
- A person shouldn’t travel from a place where there’s a minyan to a place where there’s no minyan unless there’s a serious health need, parnasa (financial support for oneself and family) need, or mitzvah need.  However one should not go on a tiyul (trip) if it means missing praying with a minyan. 
Missing minyan in order to host guests
- Don’t leave a guest in order to go daven because welcoming guests (hachsanat orchim) overrides davening in a minyan. 
Missing Minyan in order to daven vatikin
- Someone who usually davens Vatikin should daven vatikin even if one day he can’t get a minyan. 
Missing minyan because one is sick
- One is only exempt in cases of extenuating circumstances such as someone not feeling well and even in such a case one should pray at the time of the Tzibbur. 
Missing minyan because of learning
- For someone who’s learn is his “occupation” meaning that one doesn’t waste anytime from learning except for the absolutely necessary activities, may daven not in a minyan from time to time, however, nowadays using this leniency is highly discouraged.  Therefore, even if one is involved in learning one should make sure to daven with a minyan and there’s an added seriousness for such a person to daven with a minyan so that others don’t judge him incorrectly or mistakenly learn that minyan is unimportant. 
- If one came late to the set minyan and going to a later one will cause you to miss learning in a chevruta. 
- If it’s going to cause a loss of teaching Torah in public such as if one will miss giving a public shuir, one should miss minyan in order not to miss that opportunity. 
- S”A 90:9 writes that a person should make a serious effort to daven with a minyan and one is only exempt in extenuating circumstances. Mishna Brurah 90:28 emphasizes the important of Davening with a minyan and that the most important part of Davening with a minayn is Shemoneh Esrei. Kitzur S"A 12:7 writes that Hashem doesn't reject the Tefillah of a congregation even if there are wicked people in the congregation. See Halichot Shlomo (chapter 5 note 52 pg 66) who records an incident in which for health reasons a certain person was only able to leave the house once a day and Rav Shlomo Zalman said he can use that one time to go to work instead of going to daven in a minyan because being social will make him feel better.
- S"A 55:1
- S"A 69:1 Mishna Brurah 69:8, Yalkut Yosef (90:14, Sherit Yosef 2 pg 341)
- Halacha Brurah 55:18-9, Mishna Brurah 55:32
- Kitzur S”A 15:10
- Kitzur S”A 15:10
- Kitzur S”A 15:10
- Kitzur S”A 15:10
- Mishna Brurah 90:29
- Halichot Shlomo (5:4 pg 61) writes that for parnasa, health, or mitzvah needs one may travel to a place where one won’t be able to find a minyan.
- Theoretical discussion: [Rav Zalman Nechemyah Goldberg (Halichot Shlomo (page 72 and 358) at first writes that seemingly it would be permissible to put oneself in a situation where one will be without a minyan as long as the time for that tefillah didn't arrive similar to the Baal HaMoer who permits boarding a boat 3 days before Shabbat even if one will need to violate Shabbat for Pikuach Nefesh. (The reason for 3 days is that there is an extension of Shabbat into the last three days of the week, however, the obligation of tefillah only applies at the time of prayer). However, he strongly rejects this by saying that putting oneself in a situation of missing praying with a minyan because it would be out of one's control to get a minyan in one's destination is totally dissimilar to violating Shabbat for Pikuach Nefesh which is permitted. He says that going to such a place is like not building a sukkah for sukkot and trying to claim that it's out of one's control to sit in the sukkah. He continues that perhaps the exemption from traveling more than a mil to find a minyan isn't because that it's out of one's control but that the obligation of minyan was removed by chazal for someone at such a distance similar to someone beyond a certain distance at the time of korban pesach, then perhaps there wouldn't be a prohibition to put oneself in such a situation. He leaves the question whether there's an obligation to find oneself in a place where there's a minyan (before the time of tefillah) unanswered, nonetheless, it's certain that the correct righteous practice would be not to put oneself in such a situation.] Rabbi Aryeh Lebowitz explained that this question would be dependent on another dispute whether davening in a minyan in an absolute obligation or a added feature to davening.
- Rav Nevinsal in BeYitzchak Yikra 90:18
- Halichot Shlomo (chapter 5 note 25 pg 66)
- Halichot Shlomo 5:17
- S”A 90:9, Mishna Brurah 90:29
- Rama 90:18, Mishna Brurah 90:56, Piskei Teshuvot 90:23 writes that this leniency is discouraged but there is what to rely on and quotes the son of the Chafetz Chaim who writes about his father when writing the Mishna Brurah would go ten hours at a time learning without eating or even stopping for mincha.
- S”A 90:18, Mishna Brurah 90:29, 57, See Sh”t Igrot Moshe 2:27 regarding missing minyan for learning
- Mishna Brurah 90:56 writes that one who is going to give a shuir to the public may not miss out on the opportunity in order to go to a minyan. Halichot Shlomo 5:16 adds that even if one will only miss learning with a chevruta one shouldn’t go to the minyan; BeYitzchak Yikra (Rav Nevinsal) 90:18 writes that if a student in a yeshiva eats and sleeps by the yeshiva it’s an imperative to daven in the Yeshiva minyan and it’s forbidden to daven even in a holier place such as by the kotel because of Mitzvah HaBah BeAvierah!
- Mishna Brurah 90:56 writes that one who is going to give a shuir to the public may not miss out on the opportunity in order to go to a minyan.