Contamination at a distance through empty space is found in two similar modes in rabbinic law: in relation to a corpse, and in relation to a ‘leper’. In both cases, the presence of the source of impurity within an enclosed space causes the contents of the space to become unclean even when untouched by the source of impurity. There are, however, some intriguing differences between the impurity effects caused by a corpse in a ‘tent’ ('ohel) and those caused by a leper in a ‘habitation’ (moshab). Is it possible to see a rationale in these two contrasting patterns? In particular, why does the law of ‘overshadowing’, characteristic of corpse-impurity, have no place in the law of leper-impurity?

The law of overshadowing is different from the law of the tent. Overshadowing takes place in the open air (or within a solid block of stone, earth or other material), not in an enclosed space. Its meaning is that if a person or vessel is situated vertically above or below a corpse, or piece of a corpse, then that person or vessel becomes contaminated. This contamination has no spatial limit. It operates only vertically: anything situated to the side of the corpse, even if only a foot away, is unaffected.

In a tent, or enclosed space, as we have seen, contamination affects even persons or objects not vertically above the corpse, provided that they are situated somewhere in the same enclosed area or tent, but the movement of contamination in an upward direction goes only as far as the ceiling of the tent.