By Aharon Gabbay

Maran Harav Yosef Karo writes in Orach chaim 55/1: 10 people are required for barchu, kedsuha and kaddish. Since these are a ‘davar skebekedusha’ (holy procedure) because of the holiness mentioned in them, therefore it is required for 10 people to be present while reciting these prayers. The Mishnah Berurah says that the same is also with the whole chazzarat hashsats that 10 is needed to say it. Furthermore, the Mishna Berurua says that there are no less 7 times in the day that we say kaddish:

1) after yishtabah,

2) ‘chatsi kadesh’ after the chazarah,

3) ‘kadish titkabal’ ,

4) after ‘aleinu’ since it has some pesukim within it,

5) after ‘ashrei’ in teffilat minchah,

6) after mincha,

7) in arvit after the ‘shema’ before the ‘amidah’.

Having said that, Maran adds in 55/2 that if one began kaddish or kedusha with 10 people and one or more left, that kaddish can be completed as long as a majority (6) remain. The ruling is as long as the congregation are still reciting the same ‘inyan’ (topic) they can carry on even if they are less than 10. However, in a case where chazzarat hashats began and one person left and there are cohanim present, since birkat cohanim is a separate inyan, 10 would be required again in order to say it. Nevertheless, if the prayer ‘elokenu ve’elokay avotenu’ was said (when no cohanim are present) 10 are not required again.