Mourning with the Mourner
Sadly, the subject of this post was הלכה למעשה for me this past week. I'd like to dedicate it to the memory of my paternal grandfather, Max Cohen, מלך בן ישראל עוזר הלוי ז"ל, who left this world on י"א טבת תשס"ה.
The הלכה, ostensibely following the חכמים (in the ברייתא brought on
:מועד קטן כ) is that "כל שמתאבל עליו מתאבל עמו." When a person for whom one would mourn (based on one's family relationship) is in mourning, one mourns with that person (with the exception of one's spouse, whom one joins in mourning only when it is for his/her parents).
Already from the time of the ראשונים, it was customary not to practice this in full. The assumption is that the requirement was only out respect for the mourner, and the mourner can choose to waive this requirement. Nowadays, since the accepted custom is to waive the requirement, we can assume by default that the mourner has done so. All that remains is the custom, recorded by the תרמת הדשן (in שו"ת סימן רצא) as the practice of the גדולים of Austria, and codified (שו"ע יו"ד שעד:ו) by the רמ"א, for the mourner's relatives to observe certain שלושים-like restrictions until the first שבת after the burial.
Nonetheless, some analysis of this הלכה in its original form can help shed light on views of how it should be observed in its modified form today. The רמב"ן writes (תורת האדם - שער האבל - ענין קרובים המתאבלים) that though the custom in his time was already not to observe this at all, מעיקר הדין, the mourner's relative should observe most mourning practices even outside the mourner's presence. He reconciles this with the position of חכמים in the ברייתא mentioned above, by saying that the אבל would still be conscious of his relative were coming into the house freshly bathed with clean clothes, or putting on his leather shoes to leave the house, so even some of the relative's activities outside the house are considered to be "in the presence" of the אבל. However, if we can say that the רמב"ן had a מסורה for how the הלכה was to be implemented, but not neccesarily for the source, then a simpler explanation would be that it reflects the position of רבי עקיבא in that ברייתא. (Is it feasible that one could apply the rule of "הלכה כרבי עקיבא מחביריו" here even though the חכמים are not mentioned by name?)
For חכמים, this הלכה reflects the relative's relationship to the אבל, for whom it is not conducive to a state of mourning to see those closest to him going on normally with life. For ר' עקיבא, on the other hand, it reflects the fact that the second-degree relative, too, had a family relationship with the deceased, and it gives expression to the grief that he, too, feels over the loss.
One "נפקא מינה" for us is whether we accept the addition (יו"ד שעד:ה) by the ב"ח of attendence at festive meals to the list given by the תרומת הדשן of restrictions that are still observed nowadays. Another one would be whether any restricitons at all should be observed if the second-degree relative will not be seeing the אבל at all, and certainly if the relative who "linked" him to the deceased is on longer living.

