794. A Kaddish Quorum in Question
A minyan (quorum of ten men) is required for the recitation of Kaddish. When visiting the beis hachayim (cemetery) on the day of a yahrtzeit (anniversary of death), there may not be ten men readily available to form a minyan at the gravesite, though there may be others in the vicinity, people scattered afield at other kevarim (graves). Similarly, when reciting Kaddish in a large shul there may be people around aside from the core group of mispallelim (those praying), but they are not gathered close since they have already completed davening or are presently learning.
Halachah states that as long as there are a total of ten people present within certain parameters, the recitation of Kaddish may proceed. The division must be as follows: at least five of the ten men must be available to answer to Kaddish (so that when including the one reciting Kaddish, there are six men totaling the majority of a minyan), while the other four men must be within eyesight. As long as the “extra” men are within range, they do not have to actually hear the words of Kaddish being recited. (At times, nine must necessarily answer the tefillos and not just six – see Halachah #509 and Halachah #696).
However, for this ad hoc Kaddish minyan to progress, it must be ascertained that there's no derech harabim (wide public pathway) separating anyone who is being counted as part of the group of ten. Aisles in a shul that are meant for ease of navigation are permissible, but not a major thoroughfare used as an exit. The same is true of small paths within a cemetery that separate the core of six men from the others, especially when all the kevarim are surrounded by a fence demarcating the area.